CHAPTER II
Ballistic Characteristics of Wounding Agents
Maj. Ralph W. French, MAC, USA (Ret.), and Brig. Gen. GeorgeR. Callender, USA (Ret.)
PHYSICAL ASPECTS OF THE MISSILE CASUALTY
Warfare between individuals or nations to be carried to asuccessful conclusion requires rendering the enemy noncombatant through injury,or death, and concomitant loss of his ability to function within his assignedduties. In modern warfare, antipersonnel weapons have been developed which arecapable of injuring the enemy at a considerable distance from the origin ofattack, and means, such as the atomic bomb, have been devised for the wholesaledestruction of enemy personnel and materiel. While destruction of materiel playsa role in modern warfare, inflicting injury to cause incapacitation of personnelstill remains the most important consideration.
To develop perspective for fair appreciation of modernwarfare and its weapons, it is necessary to go back to prehistoric time. It islogical to presume that the earliest warfare was hand-to-hand combat. This wasprobably quickly augmented by sticks, clubs, or other similar and readilyavailable aids. Following this, prehistoric man no doubt commenced to hurlstones or other missiles easily grasped and thrown. From this stage, it was nottoo great a step to increasing missile velocity through the aid of the sling,throwing stick, or other means to add to the missile velocity and consequenteffectiveness. In brief, man took advantage of the physical law of kineticenergy which remains as the fundamental law in the study of missiles and theformation of wounds.
Considering early history as recorded in the Bible, it isnoted that David, in his encounter with the giant, Goliath, was conversant withthe advantage to be gained through augmenting his personal strength with small,smooth stones which could be hurled effectively with the sling. This offset theinherent advantage of the giant's strength. It resulted in a missile casualty.
As we come down through recorded military history, we see manaiding his military effectiveness in rendering the enemy hors de combat with thehand-hurled spear or javelin followed by the arrow propelled by the bow orcrossbow. In this stage, we see man also adding to his ability by using thehorse as a means for increased velocity and force in propelling the spear.However, the arrow was often capable of inflecting injury at greater ranges thanpossible for hand-to-hand encounter and had excellent ballistic qualities. Inthis period, there
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also was the use of various antimateriel weapons, such as thecatapult for throwing stones. Ever since this era, there has been a decrease inthe size of the missile and an increase in velocity and consequent range ofeffectiveness.
With the advent of gunpowder at the battle of Cr?cy in the14th century, the potential for greatly increased missile velocities withability to produce injuries at greater ranges became apparent. However,development was relatively slow, as gunpowder in its earliest applications wasoften more dangerous to friend than to foe. Metallurgy, chemistry, physics, andthe manufacture of weapons had yet to be developed to permit the commonplaceapplications of modern warfare.
The gunpowder available for many years was dangerous as itsrate of transformation into gas could not be accurately controlled and as italso deteriorated on slight provocation. This resulted in many serious disastersthrough weapon failure. Only with the advent of the so-called smokeless powderscould rate of burning be controlled and pressures be held within safe limits.
From the 14th to the 19th centuries was seen the developmentof small arms through the blunderbuss, musket, and rifle and the development ofartillery from the crude wooden cannon to the metal smoothbore and the rifledartillery piece. Smokeless powder with its controllable rate of burning was a19th century invention. In this period also was seen the use of explosivecharges in grenades and landmines, as well as the development of explosivemissiles for artillery use.
In the 20th century came the airplane with its potentialitiesof transporting bombs many miles from the point of origin to inflict injury onenemy personnel and to destroy materiel. There also was marked improvement inpowders and other explosive agents.
Analytical retrospection of the entire development of warfarefrom prehistoric time reveals man's continual struggle to augment his humancapability to inflict injury through the utilization of the law of kineticenergy as applied to the moving object. There is a continual trend down throughthe centuries toward the infliction of injury at even greater distances throughincrease in missile velocity. In this respect, the airplane is only an agent tocarry the missile of destruction to yet greater distances from the point oforigin. It results in greatly increased effective battle ranges.
Along with this general trend, it also is noted that anincreasingly greater number of people are involved in major military operationswith ever-increasing effort toward the development of more and more firepower.
Missile effectiveness has been observed to be a function ofvelocity, and, in keeping with this, it was but natural that through the agesthere has been a continual increase in missile speeds. Before the advent ofgunpowder, missile velocities at best could not exceed several hundred feet persecond. From the 14th to the beginning of the 20th century, missile velocitieswere increased to approximately 2,000 f.p.s. (feet per second). In the period1900-1918, velocities were again increased up to approximately 4,000 f.p.s. Fromthat
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date to 1953, and taking the atomic bomb into consideration,missile velocities have been increased to approximately 20,000 miles a second.No doubt some of the radiation components of the atomic bomb have greatervelocities than this. However, gunpowder and its related agents were responsibleonly for a velocity increase to something more than 7,000 f.p.s., the greaterincrease being due solely to the nature of atomic fission and its reactions.
Progressively, the outstanding steps in this analysis ofmissile warfare and its development down through time follow: Clubs, stones,sling, bow to propel an arrow, gunpowder, rifle, smokeless powder, TNT andrelated propellants, airplane, rockets and rocket-propelled bombs, and theatomic bomb.
From this brief r?sum? of the progressive development ofthe missile as an antipersonnel agent, it is natural to inquire just how thatmissile produces a casualty. While medical men have served with the armies formany years, it was only recently that studies to determine the mechanics ofwound production have been instituted. There has been some observation and manyreports but little organized research, mainly because available instrumentationwas inadequate for a serious, comprehensive study.
Better appreciation of the detailed mechanics of woundproduction has a dual purpose. First, a more complete knowledge of the wound andits extent permits better definitive treatment by the military surgeon; second,this knowledge permits the design of ordnance materiel for antipersonnelpurposes on scientific grounds. It also lessens the need for costlyrule-of-thumb or "cut and try" methods by either the military surgeonor the ordnance engineer.
It is the purpose of this chapter to bring together thesalient principles regarding the missile casualty as a physical entity, a causeand effect phenomenon. These principles explain many apparent anomalies as seenby the surgeon unacquainted with the detailed mechanics of wound formation andmay aid the ordnance engineer in his design problems.
Frequently, the military surgeon has seen small entrance andexit holes in the skin of a gunshot casualty and taken it for granted that theinternal damage was correspondingly small. Had he known more of the modernhigh-velocity rifle bullet and what is known as yaw, the trivial external woundswould not have misled him in his initial treatment of the wound. Also, had hebeen appreciative of the true magnitude of the forces involved, his mentalpicture of the wound would have been far more accurate.
For many years, the ordnance designer gaged theeffectiveness of missiles by their ability to penetrate pine boards or similarmaterials. However, when an accidental discharge of a shrapnel round raised aserious doubt as to the real value of shrapnel as an antipersonnel agent, thisrule-of-thumb gage was found to be valueless as a criterion. The ordnancedesigner wanted some "real" information from the medical man of whatwas necessary to produce a casualty.
For the sake of a comparable yardstick in evaluation ofordnance materiel, a missile with 58 ft.-lb. (foot pounds) of kinetic energy wasconsidered to be capable of producing a casualty. While this has not been fullysubstantiated
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as a fair criterion, it is well supported1 and isdefinitely superior to pine boards. No doubt, under optimal conditions, amissile with considerably less energy than 58 ft.-lb. can produce a seriouswound, but on the average it is probable that this amount of energy will insurea casualty.
Though much has been accomplished in a comparatively shorttime in explaining many of the factors entering into the physical formation ofthe wound, much remains to be learned. There is the question of how the yawingrifle bullet produces such damaging injuries. There also is the question ofnerve injuries-their cause, extent, and repair. Again, just how muchdebridement is necessary to insure repair? These are but a few of the physical,physiological, and pathological problems yet to be answered.
The Missile Source2
Small arms.-In considering the missile casualty, smallarms naturally fall into several classifications based on the character ofwound. For the purpose of this discussion, small arms will be considered asthose weapons so classified by the Office of the Chief of Ordnance, U.S. Army,with a caliber of approximately 0.60 inch or less.
Sidearms.-These are small weapons designed primarilyfor personal defense. In World War II, some automatic weapons in this categoryalso were designed for effective offensive employment at near ranges. Muzzlevelocities ranged from a little more than 800 f.p.s. for the U.S. sidearms up tonearly 1,200 f.p.s. for those used by the Germans. The comparatively lowvelocities produced minimal wounds.
Carbine.-In the U.S. Army, the .45 caliber pistolwas often replaced by a .30 caliber carbine firing a 110-grain bullet with amuzzle velocity of 1,975 feet per second. This was a semiautomatic weapon usefulfor offensive as well as defensive action. It also was used by paratroopers andothers requiring a small, effective weapon. While essentially a shoulder weapon,the ballistic characteristics placed it more in the category of a super sidearm,and missile casualties from this weapon were more of the sidearm type.
Shoulder weapons.-The basic offensive weapon of thefoot soldier is the shoulder weapon. From the lessons learned in World War I,the trend in military weapons has been toward the development of semiautomaticarms to relieve the soldier of the interruption due to loading the weapon.Consequently, there has been an increase in the rate of aimed fire andfirepower. However, many repeating rifles of the older magazine type were usedin World War II. From the missile-casualty standpoint, the most importantconsider-
1The 58 ft.-lb. rule was never completely acceptable to all the workers in the field, and a major effort has been initiated to supplant this rule with more definitive medical criteria. The 58 ft.-lb. of kinetic energy was based upon an early German principle and probably was meant to be applicable only to lead spheres weighing half an ounce and measuring half an inch in diameter.-J. C. B.
2(1) Catalogue of Standard Items. 2d ed. Office of the Chief of Ordnance, Washington, D.C., 1944, vols. I, II, and III. (2) Catalogue of Enemy Ordnance Materiel, Office of the Chief of Ordnance, Washington, D.C., 1945, vol. I (German); vol. II (Japanese).
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ation is the muzzle velocity of the shoulder weaponprojectile, as this largely determines the effective range and the type ofwound. In World War II, the muzzle velocities of the Japanese rifles ranged from2,200 to 2,400 f.p.s.; of the German rifles, from 2,500 to 2,700 f.p.s.; and themuzzle velocities of some of the U.S. shoulder rifles were slightly more than2,800 f.p.s. In general, at combat ranges, comparatively severe wounds are to beexpected from any of these weapons, much more so than the wound produced withthe usual sidearms missile and velocity.
Machineguns.-In the machinegun category are theantipersonnel full automatic weapons using essentially the same ammunition asthe shoulder weapons of corresponding caliber. Weapons of this type in thelarger calibers are primarily antimateriel agents and will be considered laterin their secondary antipersonnel aspect. As a missile-casualty agent,machineguns are essentially the same as shoulder weapons except for oneimportant factor. Full automatic weapons fire at a high cyclic rate, 400-800rounds a minute. This commonly results in multiple wounds, all of a severity tobe expected with the shoulder weapon missile. This also accounts for the factthat the machinegun missiles proportionately produce a greater number of fatalcasualties.
Automatic weapons larger than 8 mm. (0.315 in.).-Whileclassed as small arms, weapons in this category (most of them 0.50 inch incaliber) are designed primarily for aircraft, AA (antiaircraft), andantimateriel purposes. The larger size of projectile permits the practical useof an HE (high explosive) bullet as well as other types of missiles designed forspecific purposes. While some wounds are certain to be caused by these missiles,the casualty is usually incidental to the use of the weapon for other missions.
Antitank small arms.-The Germans had three types of7.92 mm. (0.312 in.) nonautomatic AT (antitank) guns of interest. One, anex-Polish model, had a muzzle velocity of 4,100 f.p.s., while the other two hadmuzzle velocities of 3,540 f.p.s. Early in World War II, these weapons werequite effective and were capable of penetrating more than an inch of armor at arange of 100 yards. However, with the increase of tank armor protection, theylost their value and became effective only against light-armored vehicles. Thehigh-muzzle velocities are of interest, though it is unlikely that many missilecasualties can be ascribed to these weapons.
Ammunition.-For sidearms and shoulder weapons,ball-type ammunition is generally employed. This usually consists of a lead coreprotected with a jacket of gilding metal or similar material. Most bullets inmilitary use are sharp pointed, having the so-called spitzer nose. Some have aflat base while others are boattailed. Some medium-velocity ball ammunition isused with the carbines or other special defensive weapons.
Small arms ammunition commonly used with machineguns andaircraft and AA weapons in the small arms category includes:
1. Ball ammunition.
2. Incendiary ammunition.
3. Incendiary with tracer ammunition.
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4. Tracer ammunition.
5. Armor-piercing ammunition.
6. Ball with tracer ammunition.
7. High explosive ammunition.
While casualties may occur with any or all of these varioustypes of bullets, other than ball, the primary use of these bullets is for otherpurposes. Most of the varied types of ammunition find their greatest use inaircraft and AA work. However, under certain ground conditions, tracer,incendiary, and AP (armor-piercing) types are of value in machinegun missions.
Wounds resulting from tracer, incendiary, or HE bullets arecomplicated by various effects peculiar to the particular missile. Tracer andincendiary bullets not only introduce the factors peculiar to their chemicalcharacteristics but usually produce severe wounds because of their comparativelack of stability, their low cohesiveness, and their poor ballisticcharacteristics resulting from loss of mass. They often yaw badly and break upon impact. Wounds often suggest the use of explosive bullets. Whileinternational agreement had prescribed the HE missile for small arms use, theJapanese had such bullets for their 7.7 and 12.7 mm. weapons, presumably for usein aircraft and AA weapons. However, in view of the fact that aircraft oftenstrafed personnel, the complaint regarding wounds from HE bullets was logical.
Japanese 6.5 mm. bullet with enlarged core in the base.-Incorrespondence,3 it was suggestedthat this bullet was probably launched at velocities higher than those usuallycredited to the Japanese 6.5 mm. ammunition. This was believed erroneous becauseof the weight of the bullet. The 6.5 mm. rifle was a comparatively old gun, andno doubt materials inferior to those available in modern weapons had been usedin its construction. It also was not designed for chamber pressures common inmore modern weapons. The bullet weighed 138 grains (figs. 45 and 46) and washomologous with a 161-grain .30 caliber bullet. A bullet homologous with the150-grain .30 caliber bullet would weigh 129 grains.
Knowing the chamber pressures necessary to launch a 161-grainbullet in the .30 caliber rifle with a velocity comparable to the 150-grainbullet, it was logical to presume that the Japanese fired this bullet at amuzzle velocity of 2,300-2,400 f.p.s., usually credited to their standard137.3-grain bullet.
However, the spin imparted to the bullet by the rifling wouldhave a negligible effect in effecting stabilization in denser mediums, such astissues. In fact, the increased mass in the tail of the bullet wouldundoubtedly operate to increase greatly the degree of yaw on entering a densemedium. This bullet would probably have slightly less stability in air than oneof a more conventional design, so that the degree of yaw on impact wouldnormally be somewhat larger also.
3Memorandum, Deputy Chief, Small Arms Development Branch, Technical Division, Office of Chief of Ordnance, 19 Feb. 1943, for Col. George R. Callender, MC, Army Medical Center, Washington, D.C., subject: Japanese Caliber .256 Bullets, with enclosures thereto.
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In general, it has been observed that with sufficientvelocity all cored metal-jacketed bullets will break up or deform on impact. Themost resistant to disintegration is the sharp-pointed spitzer bullet. However,at close ranges and impact velocities in excess of 2,400 f.p.s., this bulletoften shows deformation, with breakup appearing first in the base of thebullet. On the other hand, the round-nosed bullets break up at velocities from 1to 2 thousand feet less, but their first deformation occurs at the nose. Bulletbreakup or deformation of the full metal patch missile is most apt to occur onimpact with hard bone.
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Soft-nose hunting-type bullets break up at lower velocitiesand often commence to disintegrate in the skin immediately after impact.Fragments of jacket and lead core are found in quite superficial tissues whenimpact velocities are excessively high-2,200 f.p.s. or more.
Projectile, artillery.-Although in all wars beforeWorld War II various antipersonnel loads such as canister, grapeshot, chainshot, and shrapnel were used, experience had conclusively demonstrated thecomparative ineffectiveness of these agents for antipersonnel purposes. The HEprojectile, however, had proved to be not only more effective in producingcasualties but had also proved capable at the same time of inflicting materieldamage which is often of greater importance in carrying out the artillerymission.
The HE projectile is capable not only of penetrating anearthwork but, after the penetration, of detonating and producing casualties inthe personnel, supposedly protected by the earthwork, by the many high-velocityfragments resulting from the detonation. Various types of contact, delayedaction, and time fuzes permit almost uncanny timing of projectile detonation.
Ineffectiveness of the special antipersonnel cannon loads hasbeen due in the past to the comparatively low projectile velocities at battleranges. Though this was not so apparent at the battle ranges common to warfarebefore the 20th century, it became a certainty with the experiences of World WarI. The advent of smokeless powder, better types of steel, and manufacturingimprovements made practicable increased artillery muzzle velocities, but thesefactors did not materially increase the effective remaining projectilevelocities. The battle ranges increased commensurately with the increase inmuzzle velocities so that remaining velocities remained essentially constant.
On the other hand, fragments resulting from the detonation ofHE projectiles have increased materially in effectiveness as antipersonnelagents. Control of burst has been much improved through more accurate fuzing.Initial fragment velocities have been more than doubled (from less than 3,000 tomore than 6,000 f.p.s.) by the utilization of new explosives. Fragmentation hasbeen controlled also through improved projectile design and through theselection of better fragmenting materials in construction.
High-explosive detonation charges have resulted in a muchgreater number of effective fragments than was possible with the other types ofantipersonnel projectiles. For instance, the total number of balls in a 3-inchshrapnel load was less than 300 compared to the thousand-odd effective fragmentsfrom a 75 mm. HE shell at 20 feet from the point of burst. The 81 mm. HE shellwith an initial fragment velocity of 6,180 f.p.s. has more than 2,500 effectivefragments at a distance of 20 feet from the point of burst. The fragmentdistribution from HE projectiles also covers a greater area than shrapnel balls.
Casualties resulting from high velocity HE fragments sustainmore severe wounds than do those resulting from the relatively low velocityshrapnel balls. In fact, shrapnel velocities were often so low that neitherclothing nor skin penetration was effected within a few yards of the burst.
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Though the application came in the latter part of World WarII, the use of the radar proximity fuze materially enhanced the value of the HEprojectile as an antipersonnel weapon. It insured the burst's occurring underoptimum conditions for casualty production. This development undoubtedly pointsthe way to the HE projectile's being used much more in the future as aspecific antipersonnel weapon. Somewhat similar effects were noted in junglewarfare when fuzed projectiles were detonated by contact with the trees. Ineffect, this resulted in an airburst under optimum conditions.
A canister projectile was used in the 37 mm. gun at closeranges against tank personnel. The canister was loaded with 122 lead ballsweighing approximately 100 grains each. Velocity was imparted to the balls bythe 2,500 f.p.s. muzzle velocity of the canister. This load could only beeffective at pointblank ranges where remaining velocities would be adequate. Thecanister was designed to release the balls immediately on firing, so rapidretardation of the balls could be anticipated because of the lack of desirableballistic characteristics.
In artillery work, the only other projectiles usually usedwere the shot or AP loads and various chemical loads, such as flare and smoke.These loads have little significance as antipersonnel agents, casualties onlybeing incidental to their primary purpose. Of course, some casualties resultfrom direct hits by AP projectiles as well as by the secondary missilesresulting from their impact. In some phases of tank warfare, both can be majorcauses of tank casualties. Both also may be significant in naval warfare.
The Japanese still used some shrapnel of conventional designwith their 75, 105, and 150 mm. guns. At near ranges in jungle fighting,shrapnel could have greater antipersonnel value as the remaining projectilevelocity added to the initial velocity imparted to the shrapnel balls by theblack powder bursting charge could make the balls effective missiles for a shortdistance. However, the usual muzzle velocity of Japanese artillery was low ascompared with that common to modern weapons. It is apparent that the Japanesewere either not cognizant of the value of velocity or were unable to produceweapons capable of sustaining the higher powder pressures necessary to securethe increased muzzle velocities.
The Germans had an interesting and effective antipersonnel 8cm. HE mortar shell known as the "Bouncing Betty." On impact, anondelay fuze ignited a smokeless powder charge which in turn ignited a delaypellet. The explosion of the smokeless powder charge sheared off pins holdingthe nose cap to the projectile body and threw the shell from 5 to 10 feet intothe air. In the meantime, through the action of the delay pellet and a boostercharge, the main TNT bursting charge was detonated at approximately the momentthe projectile was at the height of its bounce. This was a simple means toobtain the effect of an airburst. Initial fragment velocities with TNT ofapproximately 3,500-4,000 f.p.s. resulted in effective fragment distribution fora considerable range.
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Aerial Bombs4
Though World War I saw the first application of the airplaneto warfare, it remained for World War II to demonstrate its use as a formidablemilitary weapon. Personnel were attacked in one of two ways: By gunfire instrafing or by aerial bombs.
Missile casualties due to strafing have characteristicstypical of small arms injuries except for several possible details. The speed ofthe airplane can add to wound severity by augmenting the bullet velocity by asmuch as 800 feet per second. Some casualties may also be due to tracer, AP,explosive, or other special bullets commonly used in airplane weapons. Anotherimportant factor is excessive yaw, as many gun barrels are in such a conditionthat the bullets are not stabilized. In rapid fire, the generated heat alsoexpands the barrel to such an extent that the bullet may not follow the rifling.
Peculiar to the airplane as an antipersonnel weapon is theaerial bomb. While bombs are used for many other purposes, the fragmentationbombs are designed particularly for antipersonnel use. They are so constructedthat on detonation there will be a spray of effective fragments capable ofproducing casualties over a considerable area. These antipersonnel bombs come inseveral sizes, ranging in weight from 20 to 260 pounds each.
Fragmentation bombs are somewhat similar to HE projectiles inthat the bursting charge constitutes approximately 10 percent of the weight ofthe bomb. However, the bomb is specially constructed to yield a greater numberof effective fragments. Fragment size is roughly controlled by design andconstruction.
At 100 feet from the point of burst, the 20-poundfragmentation bomb averages 829 effective fragments; the 90-pound bomb, 2,880;and the 260-pound bomb, 5,450 effective fragments. Because of the bomb designand the ratio of bursting charge to bomb weight, fragments are fairly large andat 100 feet from the point of burst have velocities of a little more than 1,000feet per second.
The smaller 20-pound fragmentation bombs are commonly droppedin clusters of six bombs so that a salvo effect is obtained. A single plane maysimultaneously drop a number of clusters. Planes in a group may drop their bombsall at about the same time, so that a considerable area can be blanketed witheffective fragments. Many casualties are certain to result among exposedpersonnel. Small bombs dropped simultaneously in groups are more effective thana single bomb of the same weight.
Other bombs, though not designated for antipersonnelpurposes, can cause missile casualties. The general-purpose type, usually with abursting charge approximately one-half of the bomb's weight, is often usedunder conditions in which personnel will be exposed. As an example ofperformance, the 100-pound general-purpose bomb has 3,310 effective fragments ata distance of 100 feet from the burst moving at a velocity of 1,870 feet persecond. The higher velocity makes fragments of a smaller size more effectivethan would be true
4Terminal Ballistic Data, Office of the Chief of Ordnance, Washington, D.C., 1944-45, vols. I, II, and III.
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with the fragmentation bomb. However, this bomb has a muchgreater blast effect and depends largely on that effect in accomplishing itsprimary mission.
In some of the very large light-case bombs, the detonatingcharge accounts for 75 percent of the bomb's weight. These bombs, designedparticularly for demolition work, accomplish their mission almost entirelythrough the blast effect. There also are other special-purpose bombs, such asAP, flare, and flashlight. The Germans had an AP bomb which was equipped withauxiliary rocket propulsion to give acceleration to aid in penetration.
Fragment distribution from a bombburst is fairly symmetricalwith respect to the longitudinal axis. When a bomb drops with its axis verticaland detonates on contact, fragments fly in all directions. However, most bombsactually fall with their axis at such an angle to the perpendicular that thereis considerable asymmetry in actual fragment distribution. The most dangeroussector is that from which the bomb's axis is leaning on detonation. On theopposite side from the burst, effective fragment range is much less.
Bomb detonation is effected through the action of a fuzewhich is armed when the bomb is dropped from a plane or shortly thereafter bythe action of a wind vane. Fuzes are of two basic types-instantaneous contactor delayed action. Delay may be a small fraction of a second, or it may be somedefinite longer interval. Time fuzes similar to those used with artilleryprojectiles are only used with aerial bombs carrying flares or flash powder fornight photography. It has not been practical to initiate airbursts through theuse of time fuzes as time of flight is not sufficiently constant.
Though contact fuzes are designed to functioninstantaneously, there is, in fact, some time lapse between initiation of theprimer and detonation of the bursting charge. In this interval, a bomb maypenetrate the earth to such an extent that much of the force of the explosion isexpended against the earth and upward. The earth acts in a degree to protectpersonnel. In the case of firm or impacted earth, the bomb may alsodisintergrate on impact so as to fail to function.
Obviously, for antipersonnel purposes, optimum results canonly be expected from an accurately controlled airburst over exposed personnel.Application of the proximity fuze to the aerial bomb may accomplish this.However, in World War II, the most effective antipersonnel bomb was either theproperly designed fragmentation-type or the general-purpose bomb, each neitherso large nor so heavy that dampening earth penetration would occur beforedetonation. Under some conditions, small bombs lowered by parachutes to delaythe descent were found to be particularly effective as antipersonnel weaponsagainst personnel in the open or in foxholes.
Hand and Rifle Grenades
Most hand grenades are primarily offensive weapons of thefragmentation type. Some have fairly thick cast iron walls divided into serratedsegments and others have comparatively thin steel casings. The Germans used one
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offensive hand grenade which consisted of a pressed disk ofexplosive RDX (cyclonite) and wax with a fuze inserted in a hole in the side ofthe disk. This grenade depended on blast effect alone for performance.
One of the cast iron, fragmentation-type hand grenades loadedwith TNT as a bursting charge had 254 effective fragments with an impactvelocity of nearly 2,000 f.p.s. at 20 feet from the point of burst. Many of thefragments had sharp, serrated edges and at impact velocities of nearly 2,000f.p.s. would produce severe wounds. However, velocity was rapidly retarded sothat effective range was not great.
Grenades are of various shapes, some for direct throwing,while others of the so-called potato-masher type have a wooden handle to aid inhurling. Rifle grenades are similar to hand grenades, except that they arelaunched by means of a rifle and consequently have greater range. Some specialgrenades, hand and rifle, of the AP hollow-charge type were developed for ATuse. Their value as missile-casualty agents is quite secondary.
Grenades can only be thrown or propelled to a limited range,so usefulness is restricted to certain conditions. While the range must be suchas not to endanger friendly troops with resultant fragments, it also must permitof reasonably accurate throwing. Grenades are particularly effective when tossedinto a pillbox or thrown into an occupied dugout. In World War I, hand grenadeswere especially useful in clearing trench bays. When fragmentation grenadesdetonated in close groups of personnel, casualties with severe, multiple woundsresulted.
The Japanese had a hand grenade made of terra cotta. It wascharged with 3? ounces of explosive which would burst the terra cotta containerinto fragments dangerous at near ranges. Many of the Japanese grenades were odd,in that the fuze mechanism had to be armed by a sharp blow before hurling. Afterarming, there was a 4- to 5-second delay pending detonation.
Many hand grenades were used for the preparation ofboobytraps. Once armed, grenades are sensitive and make a dangerous boobytrapwhich cannot be easily unarmed. Severe wounds can be expected, as the victim isusually close to the explosion, where many high-velocity fragments and secondarymissiles will be the rule.
Landmines
Landmines are of two categories-AT and antipersonnel. Theformer usually requires so much weight to initiate the primer that it is oflittle direct interest as a casualty-producing agent. On the other hand, thesensitively fuzed antipersonnel mine is highly effective and is oftenresponsible for many and severe casualties.
Basically, the landmine is a defensive or protective weapon,hence more likely to inflict casualties on an advancing force. The antipersonnelmine also quickly exacts its toll of the careless or inexperienced soldier. Itmay be
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equally dangerous to friend or foe, especially when thesoldier is careless and disregards warning signs of a minefield intended toprotect a bivouac or beachhead.
Mines commonly inflict severe wounds as the victim is usuallyvery close to the detonation, often standing directly over the mine. Many lowerextremity casualties can be expected. When individuals are advancing in closeformation, a single mine can be responsible for multiple, severe casualties.Many mines not only have a considerable immediate range but often are sosensitive as to be detonated by neighboring detonations, so that the tripping ofa single mine may fire one or more in the near vicinity.
Though landmines of various types have been used in warfarealmost since the inception of gunpowder, before World War I they were crudeimprovisations. Most were comparatively ineffective. In World War I, the tankand armored vehicle on one hand and the hand grenade on the other hand naturallyled to the development of the boobytrap and antivehicle and antipersonnel mine.This development was greatly favored through the use of TNT, a powerful but atthe same time a comparatively safe explosive to handle.
Modern production methods as well as modern explosives madewholesale use of landmines both practicable and effective in World War II.Boobytrapping was developed to a new high, with grenades or antipersonnel minescommonly providing the effective part of the boobytrap. Any soldier could handledeadly TNT with impunity until it was set in place and sensitively fuzed.
Antipersonnel landmines commonly carry a charge of a pound orless of TNT or similar explosive and are generally no more than 4 to 5 inches intheir greatest dimension. They may be detonated by the direct pressure of 15 to40 pounds or by a few pounds pull on an apparently innocuous trip wire. Early inthe war, mines usually were in metallic containers, but with the development ofmagnetic mine detectors many were made of glass, earthenware, or plastic toprevent detection.
Early types depended on the fragmentation of the minecontainer and component parts together with secondary missiles of sand, pebbles,and dirt for their effectiveness. Later, mines were developed which bounced from6 to 7 feet into the air before the main detonation occurred, thereby effectingan airburst making the fragmentation effective over a much greater area. TheGermans developed several mines of this type which also carried shrapnel ballsto add to the missiles of normal casing fragmentation. One of these mines had350 steel balls weighing approximately 53 grains each. This shrapnel fillingpropelled by 8 to 16 ounces of TNT had an effective range of 150 to 200 yards.There also was a very effective wooden box German antipersonnel mine which didnot activate the magnetic mine detectors. This mine was simple and cheap toconstruct. It also was constructed in a larger size for AT use.
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Blast5
The hot gases ejected by a detonating bomb sweep out andcompress the surrounding air and throw that compressed body of air againstadjacent layers of air. In this way, a belt is formed within which the air hashigh pressure and high outward velocity. This belt is limited by an extremelysharp front (less than one-thousandth of an inch) called the shock front inwhich the pressure rises abruptly.
The shock front travels away from the point of detonationwith an extremely high initial velocity (3,000 f.p.s. at 60 feet from a4,000-pound light-case bomb where the pressure jump is 100 pounds per squareinch). The velocity then decreases rapidly towards the velocity of sound (about1,100 f.p.s.) as the shock front travels on and the pressure jump decreases.
For a better appreciation of the comparable velocity of theblast wave, it is well to consider some of the better-recognized air velocitiesencountered in winds and storms. Winds of 50-60 miles per hour are classified asgales, and in hurricanes wind velocities of 80 miles per hour are common withnow and then velocities in excess of 100 miles an hour being reported. Windvelocities in tornadoes have not been accurately recorded but are judged to beof the order of 200-300 miles per hour. The fact that tornadic winds often blowstraws into tree trunks is well established in weather bureau documents. Thehighest wind recorded by a weather bureau was slightly more than 230 miles anhour at the top of Mount Washington, N.H. Though the blast wave travels at avelocity of 4,000 f.p.s. or more when initiated, it quickly damps down to thevelocity of sound in air. This is approximately 1,100 f.p.s., the equivalent of750 miles per hour. It is due only to their very short duration that blast wavesare not far more destructive than they are in fact.
The excess pressure prevailing at a point in the air afterthe arrival of the shock front decreases and vanishes in a short time (about0.04 second at 400 feet from a 4,000-pound light-case bomb; about 0.006 secondat 50 feet from a 100-pound general-purpose bomb) and is followed by minordisturbances which often include a partial vacuum. The entire disturbanceproduced in air by the detonation of a bomb is called blast.
Peak pressure.-The peak pressure-the highest excesspressure which is attained right at the shock front-gives a measurement of themaximum force exerted against a structure by the blast (pressure X area =force).
Effects of confinements.-The presence ofobstacles which prevent the travel of blast in some directions may increase theeffect of blast in other directions.
A blast traveling along a tunnel, a corridor, a trench, and,in the case of large bombs, even along a street is effectively confined, so thatits intensity decreases much more slowly than in the open.
When a bomb detonates inside a house, demolition of the wallsmay occur even if the distance from the point of detonation to the walls exceedsthe
5See footnote 4, p. 100.
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radius of damage for the same type of bomb bursting in theopen. This is due to a variety of effects, among which is the "multiplepunch" effect created by the blasts' hitting on a wall in quicksuccession after having been reflected by other walls. If the effect of blast isintensified on one side of a wall by its confining action, it is reduced by thesame token on the opposite side of the wall by its screening action.
Protection from blast.-A wall effectively reduces blastpressure and impulses on objects close to it if it is about 10 feet by 10 feetor larger and if it is of sufficient strength to withstand the blast.
Foxholes, slit trenches, or ditches reduce the blast pressureby about 50 percent. A system of four right angles reduces it to about 15percent.
Position of the body can have a considerable influence inprotection from blast effects. Lying prone on the ground will often materiallylessen direct blast effects because of the protective defilade effects ofirregularities in the ground surface. Ground also tends to deflect some of theblast forces upward. Standing close to a wall, even on the side from which theblast is coming, also lessens some of the effect.
Many of the persons said to have been injured by blast wereactually injured through the secondary effect of being knocked down and forciblycoming in contact with the earth or with other hard objects. If the head of aperson thrown down comes in contact with a stone or similar hard object, injurymay be quite severe. Any lessening of the distance through which one falls willlessen the probable degree of injury.
Orientation of the body also affects severity of the effectof blast. Anterior exposure of the body may result in lung injury, lateralposition may result in more damage to one ear than the other, while minimaleffects are to be anticipated with the posterior surface of the body toward thesource of the blast. Defilade and reflection of the blast from the body itselfmay have some effect.
Blast pressure and the orientation of an object.-At adistance of 20 feet from the point of detonation, the peak pressure on a wallparallel to the direction of travel of the blast wave is only about one-seventhof the pressure measured on a similar wall placed at right angles to thedirection of travel of the blast. This factor varies with distance, and at 200feet from the point of detonation the ratio is about 1:2. Pressures on obliquesurfaces vary accordingly.
The effects of peak pressures (table 18) follow:
At peak pressures of 500 pounds to the square inch, 50percent killed.
At peak pressures of from 60 to 100 pounds to the squareinch, 50 percent seriously injured.
At peak pressures of 15 pounds to the square inch, eardrumsruptured.
At the nearest point, peak pressures would be between sevenand eight times greater on an object oriented at right angles to the travel ofthe shock wave; at a distance of 90 feet, the factor would be approximatelyfour; and at 150 feet, about three.
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General-purpose bomb | Pressure at- | |||||
30 feet | 60 feet | 90 feet | 120 feet | 150 feet | 180 feet | |
| Pounds |
|
|
|
|
|
|
100 | 17 | 4 | --- | --- | --- | --- |
500 | 80 | 6 | 3 | --- | --- | --- |
1,000 | 200 | 20 | 7 | 4 | --- | --- |
2,000 | 400 | 50 | 13 | 7 | 4.5 | --- |
4,000 | 1,000 | 170 | 40 | 16 | 10 | 7 |
Blast alone may cause serious injury or death at distancesfrom 120 feet for the 4,000-pound light-case bomb to less than 60 feet for the100-pound general-purpose bomb. However, it also is more than likely that withwithin such ranges bomb fragments or secondary missiles will be responsible forinjury.
Secondary Missiles
For this discussion, a secondary missile will be considered tobe a missile which has been set into motion by another or primary missile andwhich has traveled for an appreciable distance in the air or more mediums beforecausing a casualty. This eliminates body-armor fragments, pieces of clothing,and other articles on the person from consideration as secondary missiles atthis time. Fragments of bone or other tissues may be secondary missiles undercertain conditions.
Many wounds are produced by secondary missiles given theirvelocity by the blast of the primary bomb, mine, or projectile. Bullets maystrike dry sand, rock, or other material which may be moved or broken andthereby set into motion secondary missiles capable of producing a wound. Suchwounds may be comparatively trivial but painful and may be fully capable ofrendering a man a noncombatant for some time. A face peppered with sand can bequite bloody and painful, though actual injury is but skin deep.
Secondary missiles probably produce more casualties than allother causes combined in the aerial bombing of the unprotected civilian cityhabitations. Flying glass is particularly bad, even at a considerable distancefrom the source of the blast. Two factors make glass particularly bad: First, itis easily broken; and, second, the fragments are usually of a shape and typewhich will readily penetrate the flesh.
The landmine probably attains its maximum antipersonnelqualities from the many high-velocity secondary missiles of sand, dirtfragments, and other materials immediately over the mine. The way it is plantedand detonated
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is designed to make the most of the secondary missile as acasualty-producing agent. High-velocity propellents are commonly used in mines;the case holding the propellent is comparatively light; and the detonationoccurs close to the victim, often within a few inches or at most only a foot orso. Impact velocities are certain to be high.
Light secondary missiles may have high velocities,approaching the maximum possible with any given propellent. Heavier missileshave correspondingly lower velocities. Under certain conditions, for instance, arifle bullet can spall out a fragment of armor and in so doing impart to thespall a velocity greater than 50 percent of the bullet's impact velocity. Sucha spall may produce a more serious wound than the original bullet, because ofits size and sharp, irregular edges.
In the immediate vicinity of a bomb or shell detonation,large objects, such as bricks and stones, may be set in motion as secondarymissiles. Initial velocities as a rule are not so great, but their greater massgives them a considerable danger range. Lighter fragments lose velocity morerapidly.
When metal objects, such as nails, screws, and nuts, are setin motion as secondary missiles, they can produce serious wounds. Such objectshave been used in artillery projectiles as well as in the older types oflandmines (fougasse). Retardation is a function of sectional density (A/M) (p.121) and, in general, the greater the density of material the longer it willremain dangerous because of impact velocity.
Secondary missiles may be important also in connection withthe detonation of HE artillery projectiles, though normally not to the samedegree as in the case of aerial bombs, as the detonating charge is comparativelysmaller. The projectile design also favors the production of projectilefragments, which generally range farther and are a much more potent factor asa casualty producer than the secondary missile.
Probability of a Missile Casualty
From time to time, the ordnance engineer asks the militarysurgeon for an opinion on the probable effectiveness of a proposed antipersonnelagent in producing effective casualties. The ordnance engineer is also seeking amathematical expression which will permit a calculation of the probableeffectiveness of a given antipersonnel agent.
The designer of a shell or bomb can usually predetermine theprobable fragment size, velocity, and average distribution. He has also adoptedan arbitrary criterion of 58 ft.-lb. of kinetic energy as determining a fragmentwhich is capable of producing a casualty. However, he lacks mathematicalinformation as to human body vulnerability and is commonly unable to predicatevery accurately the battlefield performance of a given agent.
Some research and analysis has been attempted to bridge thisimportant gap of equal interest to the ordnance designer and military surgeon.So far, the arbitrary criterion of 58 ft.-lb. of energy for an effectivewound-producing
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missile has proved to be reasonable. It provides a basis upon which therelative effectiveness of antipersonnel agents may be compared.
Before absolute predictions are possible, however, much more must be knownabout the target. What is the target area? What proportion of that area isactually incapacitatingly vulnerable to an effective missile?
Target area is variable due to body presentation. Black, Burns, andZuckerman,6 in England, calculated the average projected area of thefull standing figure as follows:
Region: | Percent | Square feet |
Head and neck | 12 | 0.50 |
Thorax | 16 | .67 |
Abdomen | 11 | .46 |
Upper limbs | 22 | .92 |
Lower limbs | 39 | 1.65 |
| Total | 100 | 4.20 |
This projected area can vary and can be reduced to a much smaller amount asthe figure turns sidewise, kneels, or lies prone. The kneeling position presentsapproximately 55 percent of the full figure, sidewise some 45-50 percent, andthe end-on prone figure less than 25 percent of the full figure.
After determining the area of presentation, the question of incapacitatingvulnerability must be determined, as many wounds in the total body area will notnecessarily incapacitate a soldier. There is some difference of opinion as tothe proportion of this incapacitating vulnerable area. Zukerman and coworkersconsidered that some 10 to 15 percent of the projected area represented theprojection of vital organs. They also concluded that the effective vulnerablearea to small high-velocity fragments was 2.83 square feet or 67 percent of thetotal area. McMillen and Gregg,7 in an independent approach to theproblem through anatomical analysis, found the projected incapacitatingvulnerable area of the full, standing figure as follows:
Region: | Vulnerable anterior projection area as percent of total body area |
| Head and neck | 3.5 |
| Trunk | 26.0 |
| Arms | 4.5 |
| Legs | 9.0 |
| Total | 43.0 |
Relative percent of vulnerable area also varies to a marked degree with theposition of the figure. For instance, in the prone figure, head on toward themissile source, at least 75 percent of the presented area is vulnerable.
6Black, A. N., Burns, B. D., and Zuckerman, S.:Experimental Study of the Wounding Mechanism of High Velocity Missiles. Brit.M.J. 2: 872-874, 1941.
7McMillen, J. H., and Gregg, J. R.: The Energy,Mass and Velocity Which is Required of Small Missiles in Order to Produce aCasualty. National Research Council, Division of Medical Sciences, Office ofScientific Research and Development, Missile Casualties Report No. 12, 6 Nov.1945.
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Another potent variable is the angle of incidence of themissile with respect to the target area. For instance, a missile striking thethorax at a low angle of incidence will often produce a superficial wound, whileone striking more nearly at a right angle to the target will penetrate andproduce a severe wound or fatal casualty. The first may not immediatelymaterially impair the soldier's fighting ability nor require any prolongedhospitalization or treatment. The severe wound could, on the other hand,permanently remove the soldier from the fighting forces.
While the extremities account for less than one-third of theprojected vulnerable area, casualty statistics commonly ascribe well overone-halfof the casualties and resultant time lost to the service to extremity injuries.This in part is attributed to the fact that fractures are more common in theextremities and that fractures are injuries which definitely require immediateas well as prolonged treatment.
This apparent bias in wound distribution may be influenced byseveral factors. First, available casualty statistics are based on a study ofthe wounded rather than the wounded and the killed. It is well established thatmuch data based on the killed are quite erroneous.
Another variable and unknown factor which could materiallyaffect casualty statistics interpreted on the premise of random distribution ofmissiles is the degree of earth penetration effected by a projectile or bombbefore detonation. Any penetration will result in some defilade effect and inturn affect the purely random distribution of fragments. There usually is somepenetration and in soft earth it may be considerable before the bursting chargeactually functions. Where there is penetration, fragments are naturallydeflected upward by the earth surrounding the projectile. This results in someincrease in fragment density in the lower zones, while the earth surface will beprotected from fragments by the defilade effect of the earth immediatelysurrounding the projectile.
Personnel in the immediate vicinity of the burst will besubjected to a shower of high-velocity fragments from the knee level up. Manyfragments will be capable of producing severe wounds. Those hitting theextremities will often cause severe fractures, while the same fragment strikinga vital area in the soft tissues will frequently result in a fatality. Ingeneral, extremity injuries are not so fatal as those in the body or head areas.
Study of detailed statistics supports this approach to theproblem of apparent bias in casualty statistics. There is an increasing numberof fractures upward from the ground-more in the upper than in the lowerextremities, though the area of presentation of the upper is less than that ofthe lower extremities. Fractures below the knee are definitely fewer than thoseabove that point, indicating a fairly definite defilade effect as justpredicated.
Though there would often be fractures in the case of thekilled in action, it is known that only too often the statistical studies failto record them with the cause of death being ascribed to another more apparentlyfatal effect.
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Another factor in World War I fighting which could havematerially influenced the wound distribution and statistical studies was themachinegun. In many sectors, it was the practice to defend areas by cones ofmachinegun fire close to the ground level. Leg injuries would be more commonthan all others combined under such circumstances.
Fragment-damage tables,8 published by the Officeof the Chief of Ordnance, give the average distribution of effective fragmentsat various distances from the point of burst. With such tables, the distance atwhich a soldier has a given chance of being hit may be calculated. For example,a soldier is required to take a 1 to 100 chance of being hit by a fragment froma 20-pound fragmentation bomb. Suppose that the soldier is on open terrain insuch a position that a 2-square-foot area of his body is exposed to fragmentscoming directly from the bomb. Under these circumstances, the effectivefragments per square foot to which the soldier is exposed are 1/100x ? equals 0.005per square foot. From the fragment-damage table for that bomb, it is found thatthe soldier should be about 150 feet from the bombburst. In the case of the260-pound fragmentation bomb, he should be not less than 300 feet from theburst. Under similar conditions, the danger zone for a 75 mm. HE shell isapproximately 100 feet and for the 105 mm. shell between 100 and 150 feet.
Depending on the orientation of the bomb or projectile attime of burst, effective fragment distribution varies considerably from theaverage on which the cited example is based. Effect of penetration before burstalso is disregarded. In the most dangerous sector, fragment density may beincreased as much as six times the average, increasing the danger zoneseveralfold. On the other hand, in the less dangerous zones, the fragmentdensity is materially decreased.
In general, the wound factor varies something more than thesquare of the distance from the point of burst. Retardation of fragment velocityreduces the number of effective fragments, while the density per unit area ofexposure also is affected by the distance from the point of origin. Fragmentdistribution too is materially influenced when a shell or bomb penetrates theground appreciably before detonation.
The probability of a missile casualty as well as thecharacter of a missile casualty also can be expected to vary from offensive todefensive warfare. The offensive soldier is of necessity more exposed. He isforced to advance in the face of prepared zones of fire, mined areas, andvarious protective devices calculated to minimize the exposure of the defenders.
In advancing, the experienced soldier takes advantage of allpossible cover. However, he has to look for his enemy, so he must more or lessexpose his head. If ranges are sufficiently close to permit aimed shots, apreponderance of head casualties can be expected. This should be especially trueof jungle warfare.
8Terminal Ballistic Data, Officeof Chief of Ordnance, Washington, D.C., 1945, vol. III.
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The Casualty Criterion
Terminal ballistics and the missile casualty become ofimportance to the military surgeon when the ordnance engineer asks for anopinion on the probable value of any given missile in producing a casualty. Theordnance engineer also requires a significant yardstick which may bemathematically applied in developing his designs of bullets, bombs, shells,grenades, or other missile casualty-producing agents.
Technical advancement has too often demonstrated the validityof the theoretical approach in design problems to permit the olderrule-of-thumb or trial-and-error methods to be used in working up theinstruments of modern warfare. Knowing the metal and detonating charge to beused in a given bomb, the ordnance engineer can readily calculate the number offragments as well as their size and weight with probable distribution andvelocities at any given distance from the point of burst. However, a criterionas to probable effectiveness is necessary if the data just cited are to beapplied to practical design. During World War II, a criterion of a missile withweight and velocity sufficient to give it 58 ft.-lb. of kinetic energy was usedin practice.
Though the adoption of the 58 ft.-lb. figure was arbitraryor empirical, it was much more practical than using the penetration of pineboards or other inanimate objects for the purpose. Selection of the figure wasin a measure substantiated by the work of Gurney.9 This figure alsowas subsequently reasonably substantiated by the research of Harvey and hisassociates. It did supply a fully comparable yardstick on which to basetheoretically relative efficiency.
A criterion of the potential wounding possibilities of amissile was first brought to the fore in the late 1920's when bullets ofvarious calibers were under consideration in the development of a semiautomaticweapon. When this problem was presented to the U.S. Army Medical Department, itquickly became apparent that not only was there no criterion but that themilitary surgeon knew little, if anything, regarding the physical lawsunderlying the mechanics of wound formation or the production of a casualty.
For many years, ordnance engineers had been using thepenetration of 1-inch pine boards separated by a small air space (1 inch) forjudging the relative efficiency of bullets. Subsequent investigation revealedthis test to be far from precise because of variations in pine boards, as wellas many other factors beyond reasonable control. The motions of a spinningmissile vary greatly as it passes through mediums of different densities or aremodified by other variable physical characteristics. This greatly influences theretardation of the bullet and resultant conditions under which its kineticenergy is given up in the retarding material and influences the physical natureof the wound to a considerable degree.
9Gurney, R. W.: A New Casualty Criterion. Ballistic ResearchLaboratory Report No. 498, Aberdeen Proving Ground, Md., 31 Oct. 1944.
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Kinetic energy is computed from the formula mv2/2,in which m is the mass and v the velocity. It is noted thatvelocity plays much the greater part. If it is borne in mind that the usualbullet employed in military use varies in weight from around 135 to somethingmore than 200 grains, the following tabulation showing the weight of missilenecessary at various velocities to produce a kinetic energy of 58 ft.-lb. is ofinterest:
Velocity of missile | Weight of missile | Velocity of missile | Weight of missile |
F.p.s. | Grains | F.p.s. | Grains |
500 | 104.0 | 4,500 | 1.3 |
1,000 | 26.1 | 5,000 | 1.0 |
1,500 | 11.6 | 5,500 | .9 |
2,000 | 6.5 | 6,000 | .7 |
2,500 | 4.2 | 6,500 | .6 |
3,000 | 2.9 | 7,000 | .53 |
3,500 | 2.1 | 7,500 | .46 |
4,000 | 1.6 |
|
|
The fallacy of the pine-board penetration as a criterion ofmissile effectiveness was strikingly demonstrated quite accidentally when ashrapnel projectile was detonated in a close group of observers. The only realcasualty was the man holding the projectile for he lost a couple of fingers fromone hand. The shrapnel balls were well sprayed amongst the group of observers atclose range and, yet, only a few black and blue places resulted-withoutpenetration of the clothing. This total inefficiency of shrapnel was furtherdemonstrated by study of known battlefield occurrences. However, shrapnel ballshad penetrated many pine boards in the usual tests. Needless to say, themanufacture and use of shrapnel was promptly discontinued. In passing, it isalso interesting to note that there is evidence of few true shrapnel wounds inWorld War I in which many tons of shrapnel were used. So-called shrapnel woundson investigation were usually found to be due to HE missile fragments (table19).
Distribution of Effective Missiles
In discussing the probability of a missile casualty,reference was made to fragment-damage tables. These tables are based on theassumption that a projectile or bomb breaks into a certain number of effectivefragments and that the fragments are evenly distributed in all directions. Inreality, this assumption is quite fallacious.
There is a marked variation in fragment distribution, even inthe airburst. Sidewall fragmentation is quite different in character from thatof base or nose fragmentation. Even in the light-case "blockbuster"bomb, there are differences in sidewall and nose or base fragmentation becauseof the relative thickness and distribution of the metal of the bomb. There alsoare fragments of
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the fuze mechanism to be considered as these pieces areusually heavier and larger than wall fragments. They consequently have a greaterdanger range, and, while initial velocity may be slightly less, remainingvelocity is better sustained because of greater mass.
Source of fragment | Distance from burst | Initial fragment velocity | Total effective fragments | Fragments per square feet | Lightest effective fragments | |
Weight | Velocity | |||||
| Feet | F.p.s. | Number | Number | Grains | F.p.s. |
Aerial bombs: |
|
|
|
|
|
|
| 20 pounds | 80 | 2,810 | 895 | 0.0183 | 18.4 | 1,190 |
200 | 576 | .0019 | 48.6 | 731 | ||
| 90 pounds | 80 | 3,100 | 3,490 | .0712 | 15.8 | 1,280 |
200 | 1,770 | .0058 | 45.9 | 753 | ||
| 100 pounds | 80 | 7,320 | 3,943 | .0804 | 4.8 | 2,320 |
200 | 1,880 | .0061 | 27.1 | 980 | ||
| 500 pounds | 80 | 7,390 | 13,450 | .274 | 5.3 | 2,230 |
200 | 6,100 | .0199 | 26.7 | 990 | ||
Artillery projectiles: |
|
|
|
|
|
|
| 3-inch HE shell | 80 | 2,260 | 370 | .0046 | 29.3 | 943 |
| 200 | 244 | .0005 | 59.9 | 660 | |
| 90 mm. HE shell | 80 | 2,900 | 427 | .0053 | 24.1 | 1,040 |
200 | 319 | .0006 | 52.5 | 705 | ||
| 81 mm. HE shell | 80 | 3,930 | 459 | .0057 | 16.6 | 1,250 |
200 | 169 | .0003 | 45.5 | 758 | ||
| 81 mm. HE shell | 80 | 6,180 | 614 | .0076 | 9.2 | 1,680 |
200 | 112 | .0002 | 35.0 | 862 | ||
4.5-inch HE rocket shell: |
|
|
|
|
|
|
| Nose section | 80 | 3,500 | 152 | .0057 | 18.8 | 1,180 |
200 | 93 | .0006 | 47.7 | 738 | ||
| Base section | 80 | 4,000 | 353 | .0104 | 17.5 | 1,220 |
200 | 207 | .0010 | 45.5 | 758 | ||
Source: Terminal Ballistic Data, Office of Chief of Ordnance, Washington, D.C., 1945, vol. III.
Fragmentation bombs are specially designed to produce thegreatest number of effective fragments in the sidewalls. Such bombs usuallystrike in a more or less nosedown position, so that nose fragments arenecessarily forced into the ground. Tail fragments commonly fly up into the airand in falling are impelled only by the force of gravity so that their velocityis insufficient to produce more than minor casualties.
In the HE shells, both the base and the nose of theprojectile are definitely thicker than the sidewalls. Sidewalls produce manymore high-velocity fragments than either the base or nose. However, base andnose fragments, being larger, are less retarded in flight and have acorrespondingly greater danger
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range. Density of fragment distribution from the nose or baseis less than in the case of sidewall fragments.
Rocket projectiles present another anomalous situation.Depending on the type of rocket, these projectiles have a velocity of 400 to 800feet per second. They are fuzed with supersensitive fuzes so that they commonlydetonate in the air, and the remaining velocity of the rocket affects thefragment velocities. This results in a distinct butterfly pattern of fragmentdistribution. The rocket sidewall section bursts into more than twice as manyeffective fragments as compared with the nose in the 4.5-inch HE rocket shell.At 20 feet from the burst, fragment velocities vary from 2,440 to 2,570 feetper second.
Fragment-damage patterns are published by the Office of theChief of Ordnance. These show fragment distribution presupposing a graze orairburst close to the ground surface with a particular orientation of theprojectile. Even under these ideal conditions, most damage patterns are of adistinct butterfly type. In some directions from the burst, there may be veryfew fragments, while in other directions there may be many effective fragmentsof a mass capable of maintaining a dangerous velocity over a considerabledistance.
There is no allowance in the fragment-damage patterns for anyearth penetration by the projectile or bomb before detonation. However, inalmost every case, more or less penetration occurs, which materially modifiesthe damage pattern. In the case of large HE projectiles, there usually is somuch penetration that almost all of the energy of detonation is expended incratering the earth. Soldiers often expressed little fear for these largershells as their antipersonnel effect was essentially nil, barring a direct hit.
With the usual contact fuze and even with the superquickcontact type, there is sufficient delay in firing the bursting charge to permitconsiderable penetration, especially into soft earth. Standard-type fuzesoperate progressively through primer and booster to fire the detonating charge.Some time interval is required to initiate a primer which in turn initiates thebooster which fires the main charge. During the delay, the projectile or bombcan effect some penetration. For that matter, it also requires appreciable timefor the main charge to rupture the holding case and set the fragments intomotion. Slow-motion pictures readily demonstrate an appreciable timelag beforefragments are flying freely accelerated to their maximum velocity. Case rupturetakes place in a progressive manner requiring a lapse of time for itsaccomplishment.
Used only during the latter days of World War II, theproximity fuze appears to make possible the accurately controlled airburst ofartillery projectiles and perhaps aerial bombs. This application insures anairburst with a much wider distribution of effective fragments. It can beexpected that distribution will also follow a much more random pattern underthese circumstances. This type of burst obviates the loss of effective fragmentsthrough "cratering" or the defilade effect of earthpenetration.
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PHYSICAL ASPECTS OF THE MISSILE
Missile Velocity
Motion of translation, velocity, is the only factor common toall missiles. It is probably the most important single factor in consideration ofthe missile as a potential casualty-producing agent. It is the major factor inmaking the missile capable of producing a wound.
For simplicity in discussion, velocities of less than 1,200f.p.s. will be considered as low; those from 1,200 to 2,500 f.p.s., as medium;and velocities in excess of 2,500 f.p.s., as high.
Velocity is a continuously varying factor, and for ease inconsideration as a function of the missile several phases of the missiletrajectory will be discussed. First, the initial or muzzle velocity;second, the impact velocity or the speed of translation at the time themissile strikes a target; and third, the remaining (residual) or thatvelocity with which a missile leaves a target through which it has passed. Inconsidering the missile and the production of a casualty, the second and thirdtypes of velocity are the more important. The impact velocity commonlydetermines the probable severity of a wound, while the difference between theimpact and residual velocity determines the amount of energy doing work inproducing the casualty. Initial velocity is important in that it insures anadequate impact velocity at the time a missile reaches the target. It alsodetermines the probable danger range.
Initial velocity.-Initial velocity of a missile may beanything from a few feet a second up to much more than a mile a second. Smallarms missiles have muzzle velocities ranging from around 800 up toapproximately 3,000 f.p.s. Some of the recently developed AT weapons have muzzlevelocities of slightly more than 5,000 f.p.s. Bomb fragments may have initialvelocities of more than 7,000 f.p.s., and some of the fragments from HEartillery projectiles approach this initial velocity. Some artilleryprojectiles are launched with muzzle velocities greater than 3,000 f.p.s.,though most have muzzle velocities between 2,500 and 3,000 f.p.s. The 21 cm.K12 German gun was credited with a muzzle velocity of 5,330 f.p.s. and a rangein excess of 70 miles.10
In the antipersonnel weapon group, most sidearms, includingthe comparatively new carbines and small automatic weapons, launch bullets with muzzle velocities inthe low-velocity category. On the other hand,most military rifles fire ammunition with muzzle velocities from 2,400 to 2,800f.p.s. The older Japanese 6.5 mm. rifle fired ball ammunition with a muzzlevelocity of 2,400 f.p.s., while most of the U.S. rifles and those of theGermans used ammunition with muzzle velocities near 2,700 feet per second.
Investigations in the late twenties and early thirtiesdemonstrated the effectiveness of higher velocity missiles in the penetrationof armor and led to
10Catalogue of Enemy OrdnanceMateriel, Office of the Chief of Ordnance, Washington, D.C., 1945, vol. I (German), p. 100.1.
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AT weapons of small caliber with velocities ranging fromsomewhat more than 3,000 up to more than 5,000 f.p.s. The soldier's inabilityto withstand more than a certain amount of recoil coupled with excessive barrelerosion accompanying the higher velocities operated to prevent the developmentof military weapons of the sidearm or shoulder type in this category for routineuse.
High muzzle velocities in artillery weapons are seldom ofmore than didactic interest to the student of the missile casualty. Suchvelocities are usually for the purpose of increasing the effective artilleryrange, and at these excessive ranges the remaining projectile velocity is likelyto be relatively low. Missiles from artillery projectiles attain their effectivevelocity more from the bursting charge in the projectile than from the motionimparted to the projectile in firing from the artillery piece. Suffice it to saythat in general the higher the initial velocity of artillery ammunition, themore costly will be the gun that launches it. Such guns also have extremely short effective use periodswithout relining of the barrel, which is a major task.
Basically, most artillery has become primarily anantimateriel weapon with the antipersonnel characteristics only secondaryfactors. Of course, the exception to this is the target of massed men againstwhich HE artillery projectiles are highly effective and their use militarilyjustified.
Initial or muzzle velocity is of interest only to the studentof the missile casualty in that this velocity predetermines to a considerabledegree the impact or effective velocity of the missile in producing thecasualty. Once the accelerating force ceases to operate on a missile,deaccelerating forces take over, and the velocity is retarded. Retardationfactors will be discussed later in more detail (p. 120). However, proximity tothe missile source largely determines the impact velocity, and this in turn hasmuch to do with the severity of the casualty. It is this proximity which makesthe landmine a particularly vicious antipersonnel weapon. Velocities are highand missiles are many. The victim is often standing right over the mine or veryclose to it.
Impact velocity.-Of all factors to be considered in themissile casualty as a physical phenomenon, impact velocity is decidedly the mostimportant. It determines the character of the wound and in turn only too oftenthe fate of the victim. Research has demonstrated that a missile velocity offrom 125 to possibly 170 f.p.s. is necessary to effect penetration of the humanskin when using steel spheres one-sixteenth to one-fourth inch in diameter.Velocities of less than this produce only contusion without a break in theskin. Clothing also exerts a threshold penetration factor, at presentundetermined. However, it is believed to be less than that of skin, which,comparatively speaking, is quite high. Of course, amount of clothing and itsparticular nature as well as other factors will affect the threshold velocity.
In the light of available information, few missiles withimpact velocity of less than 200 f.p.s. are likely to cause more than a trivialwound in the clothed subject. Exceptions to this are the few missiles which maypenetrate vital body cavities through apertures, or the more easily penetratedportions of the anatomy such as the eye.
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The military surgeon is generally interested in missiles withimpact velocities in excess of 200 or 250 f.p.s. In practice, it is probablethat few wounds are caused by missiles with velocities much less than 500 f.p.s.,and that most of the battlefield wounds are caused by missiles with velocitiestwo and three times that figure. Some wounds are caused by missiles with impactvelocities well above 2,500 f.p.s. High explosive shell fragments account formany wounds, and these velocities are apt to be well above 3,000 f.p.s. at nearranges. With the use of the proximity fuze in antipersonnel shells and aerialbombs, many missile casualties occur from fragments with velocities of 3,000f.p.s. and upward.
With low-impact velocities, wounds are found to be relatively"cleaner" and free from the so-called explosive effect. With mediumvelocities, wounds are more extensive with considerable tissue destruction andwith some explosive effects when conditions are favorable. High-impactvelocities result in many so-called explosive wounds, with a maximum of tissuedestruction.
Superhigh velocities make small missiles deadly.Comparatively, enormous tissue damage can result from the penetration of a verysmall fragment of a grain or so in weight when propelled at the supervelocities.In English bomb incidents, it was noted that minute missiles could be forcedthrough the head with through-and-through wounds of the brain with slight, ifany, visible evidence of a wound. The victims often walked away from theincident without even so much as a headache to show for the occurrence. It isknown that the minute pins used by entomologists for the mounting of mosquitoescan be readily forced through a person's hand without evidence of blood ortrauma and without sensation to the victim.
Remaining velocity.-Remaining velocity is of importance tothe investigator in that it permits the determination of the kinetic energyexpended in the production of the wound when a missile perforates a target.When a missile fails to pass through the target, all of the kinetic energy dueto impact velocity is expended in wound formation. Apparently, the only fairmeasure of wound comparison on a physical basis is the expenditure of energy.Wounds cannot readily be compared on mere appearances alone, especiallysuperficial appearances. In practice, remaining velocity can seldom be known,while in research it should always be measured or otherwise determined insome strictly comparable manner.
Momentum, Energy, Power
There has been much speculation and some observation as tothe magnitude of the missile wound and its correlation with either the momentum,kinetic energy of the missile, or the rate with which energy does itswork (power)-all physical attributes due to velocity. Momentum is a functionof the mass times the velocity; energy a function of the mass times the squareof the velocity; and the rate of doing work or power, a function of the masstimes the cube of the velocity.
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Before modern research, factual information on the variousphysical events actually occurring in the formation of a wound was lacking.Events transpire too quickly for the human senses to perceive the details.Earlier serious research studies had been inadequately instrumented to permitrecognition of details. Results also were beclouded by the presence ofindeterminate variables, such as deforming bullets, yaw, and other form factors.
To bring out and to evaluate fundamental postulates, basicresearch was conducted with nondeforming steel balls devoid of yaw or othercomplicated form factors. Simple mediums, such as water and 20 percentgelatin block tissue models, were used, as well as animal tissues. The cathoderay oscillograph and microsecond X-ray permitted the recording and accuratemeasurement of phenomena often completed in a few microseconds.
Results from this study were carefully analyzed, and itbecame apparent that all physical phenomena connected with the wound and itsformation were direct functions of the kinetic energy doing work. Neithermomentum nor the rate with which the energy did its work (power) could becorrelated smoothly without excessive deviation with any of the various eventswhich occur in the missile wound.
Hunters have entered into many acrimonious arguments on whatconstitutes an effective bullet in the taking of game. Here some claim thatmomentum is the factor. However, this opinion is believed to be due to the factthat hunters are continually observing the effects of bullets which usuallydeform seriously or more often break up on impact. In the latter case, thegreater the mass, consequently the greater the momentum, the greater theapparent effectiveness of the bullet as it is less apt to disintegrate into suchsmall pieces as to be almost useless after penetrating the hide of the animal.It is known experimentally that this last commonly occurs with the soft-nosehunting loads at impact velocities in excess of 2,000 feet per second.11
While velocity is the most important single factor in makingthe missile potent as a casualty producer, it attains that importance onlythrough the fact that it gives the missile kinetic energy with which to producethe casualty. Physics recognizes two types of energy: Potential energy due toposition and kinetic energy due to motion. The latter is computed from theformula mv2/2 (p. 112). In the English system, m is inpounds and v in feet per second. The corresponding results are inabsolute units (poundals) which may be converted to the more conventional footpounds by dividing by the acceleration due to gravity, (g) or 32.2.
From the formula, it is noted that kinetic energy varies asthe square of the velocity. In practice, this means that doubling the velocitymultiplies available kinetic energy by four. The following tabulation gives thekinetic
11(1) Callender, G. R., and French, R. W.: WoundBallistics: Studies in the Mechanism of Wound Production by Rifle Bullets. Mil.Surgeon 77: 177-201, October 1935. (2) Callender, G. R.: Wound Ballistics:Mechanism of Production of Wounds by Small Arms Bullets and Shell Fragments. WarMed. 3: 337-350, 1943.
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energy (ft.-lb.) at different velocities for a missileweighing 100 grains and readily demonstrates why small missiles become lethal atthe higher velocities:
Velocity | Energy | Velocity | Energy |
500 | 55 | 5,000 | 5,545 |
1,000 | 222 | 6,000 | 7,985 |
2,000 | 887 | 7,000 | 10,868 |
3,000 | 1,996 | 8,000 | 14,196 |
4,000 | 3,549 |
|
|
Kinetic energy varies directly as the mass of the missile.Hence, weight is of much less importance than velocity. Doubling the weightonly doubles the energy.
Most bullets used by the military vary in weight from around150 to approximately 200 grains. The corresponding kinetic energy at the usualinitial velocities is between 1,500 and 2,500 ft.-lb., while some distance fromthe point of launching with lower impact velocities kinetic energies are muchless, usually well under 2,000 ft.-lb. and often less than 1,000 foot pounds.
Again considering the tabulation just presented, it can bereadily seen that considering the 150-200 ft.-lb. necessary for skinpenetration that, at impact velocities of 7,000 f.p.s., missiles of less than 2grains in weight are potential casualty-producing agents. This fact makes themodern bomb and artillery HE shells potent antipersonnel agents. At closeranges, there are many fragments which weigh at least 2 grains and which havevelocities of 7,000 f.p.s. or more with the newer propellents. Multiple severewounds can be expected.
With impact velocities of 5,000 f.p.s., missiles must weighnearly twice as much to have energy equivalent to those at the higher impact(7,000) velocity. However, compared to the usual military bullet, these arestill very small fragments.
The mass-velocity relationship and kinetic energy makes thelandmine a particularly vicious weapon in that fragment velocities are of theorder of 5,000 f.p.s., and there are many secondary missiles in addition to thefragments of the mine itself flying about with these supervelocities. Multiplesevere wounds are to be expected, especially when the victim trips the mine bywalking on it. In addition, there is quite an area within which missiles havevelocities in excess of 3,000 f.p.s., and small objects can continue to beserious casualty producers.
Hand grenades with initial fragment velocities of 2,900 f.p.s.produce many fragments of a weight sufficient to have adequate kinetic energy toproduce a severe wound. Grenades also are able to start effective secondarymissiles into motion.
In HE shellburst with initial fragment velocities often alittle more than 6,000 f.p.s., severe wounds are the rule. These too canreadily produce severe casualties at the closer ranges.
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Even water can be a casualty-producing missile when propelledwith sufficient velocity. One of the more efficient metal-cutting tools issimply a small stream of water under high pressure (supervelocity).
Drag, Retardation, Ballistic Coefficient
Retardation varies directly as the square of the velocityand as the diameter of the missile. It varies directly as the density of theretarding medium and inversely as the mass of the missile. These are the moreimportant factors affecting the retardation of a missile. They also largelydetermine the amount of kinetic energy which is utilized in the production of amissile casualty.
While complicated in detail, pertinent facts andrelationships can be gained from a study of the formulas regarding the missilemotions which are applicable to the military surgeon's study of the missile asa casualty-producing agent, as well as the wound as a physical entity. Thefollowing basic formulas are presented:
Drag(D)
D =rd2v2f(v/a) or D = KDrd2v2 in which r=density of the medium (1)
d=diameter of projectile f(v/a) =function v/a or KD, thedrag coefficient where v/a=Mach number
v=velocity of projectile
a=velocity of sound in the medium
This formula applies particularly to motion in air and tomissiles without particular ballistic shape, such as spheres.
For pointed projectiles the formula becomes
D= kdrd2v2f(v/a)(2)
f(v/a) is the same for all shapes
k is a constant determined by shape
d is a constant to allow for the effect of wobble, yaw, or other deviation from true flight.
Let F(v)=v2f(v/a)
F(v)=function v
M=mass
C=ballistic coefficient (ability of a projectile to overcome air resistance)
then
C = M / (kdrd2) or C = M / (id2)where i is a formfactor. (3)
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Retardation due to drag (D) then becomes
r = D / M = E(v) /C (4)
For the purpose of determining the factors controllingretardation, we will substitute the value of D in (2) for D inD/M in (4) which results in
r = (kdrd2v2f(v/a)) / M(5)In evaluating the effect of each of the several elementsaffecting retardation, the constants k and d may be disregarded. d2/Missimply another expression for the term "sectional density" (A/Mwhere A is the area). Retardation decreases as this fractionapproaches zero as a limit. Hence as d2 decreases,retardation decreases. In other words, the most efficient shape for sustainedvelocity is the needle or cylinder of maximum mass and minimum area ofpresentation.
Velocity of the moving projectile affects retardation as v2.The greater the velocity the greater the rate of retardation. Doubling thevelocity multiplies the retardation factor by four.
During the air flight of a projectile, the density, r,isconsidered to be unity under average conditions near the ground. However, whenconsidering retardation in a dense medium such as water or tissue, ris afactor of 800 or more.
Mach number, or the function v/a, is important in thatit has been determined that the velocity of sound in a medium is a criticalvelocity. Using 1,100 f.p.s. as the average velocity of sound in air near theground level, some values of v/a are tabulated:
v(f.p.s.) | v/a | v(f.p.s.) | v/a |
500 | 0.45 | 4,000 | 3.64 |
1,000 | .91 | 5,000 | 4.55 |
1,500 | 1.36 | 6,000 | 5.45 |
2,000 | 1.82 | 7,000 | 6.36 |
3,000 | 2.73 |
|
|
From this tabulation, it is immediately apparent that amissile moving in air at 7,000 f.p.s. is retarded more than six times as quicklyas the same missile moving at the rate of 1,000 f.p.s. This is an explanation ofthe fact that supervelocities and the consequent devastating wounds are only tobe encountered quite close to the point of fragment departure. Supervelocitymissiles are rapidly retarded to the lower velocities even in air.
Extrapolation of the formulas for the motion of a projectilein air to the motion in much denser mediums such as water and tissues isquestionable. Too many little known, or unknown, factors are involved. However,by
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collecting the unknown factors in KD, thedrag coefficient (CD) in a dense medium may be represented by
CD=KDrv2d2 (6)
where KD=summation of unknown factors affecting drag. r=density
v=velocity d=diameter
The drag coefficient can be determined experimentally when the velocity of amissile can be plotted against the time. Let a= the retardation coefficient andwe have
dV / dt = aV2 (7)
where V=the instantaneous velocity
and t=the time
For the determination of the drag coefficient we have:
a = (rACD) / (2M)
where r=density
A=area
M=mass
High-speed motion pictures of missiles moving in water and gelatin gel have permitted the determination ofdV/dt and from this a and inturn CD (6). The work was done with steel and aluminum spheres ranging in diameter fromone-sixteenth to one-fourth of an inch. In water, CD was found to fall between 0.30 and 0.33 from a summary of coefficient data, and the observed value was 0.314.
While it is presumed logical that f(v/a) is equallyapplicable to retardation formulas pertaining to the denser mediums, itsapplication is less important because of the usually higher value of a. Inwater, the velocity of sound is more than 4,500 f.p.s. and much greater thanthis in many metals and other hard materials. It is presumed that the velocityof sound in most tissues is similar to that in water, considering their averagecomposition and density. In view of this, at most impact velocities, the factorv/a is less than one and comparatively unimportant in affectingretardation. For example, suppose v to equal 900 f.p.s. while a is4,500 f.p.s. Then v/a equals 900/4,500 or 0.2.
This leaves as significant factors in considering retardation in densemediums, r, and A/M and v2. Compared to air,r is much greater-800 or more.A/M and v2 retaintheir same significance.
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In considering missile penetration of armor, concrete, andstone, other factors inherent in the material penetrated must be considered.Similar factors do not appear to be pertinent in tissue penetration with thepossible exception of bone. However, for our purpose, any special properties ofbone can be temporarily, at least, disregarded, as the extent of bonepenetration compared to soft-tissue damage is usually insignificant.
ShapeRandom shape.-In shell or bomb fragments, pieces ofglass, sand, and stones, missiles may have any possible shape. Few have theshapes or are so propelled that A/M or sectional density is a minimalvalue. Retardation in air is rapid. Table 20 illustrates how rapidly velocityfalls with fragments from the burst of a 100-pound general-purpose bomb (thelightest effective fragment is one capable of penetrating ?-inch mild steel).
Distance from burst | Weight of fragment | Velocity |
Feet | Ounces | F.p.s. |
20 | 0.022 | 7,320 |
30 | .029 | 6,390 |
40 | .039 | 5,660 |
60 | .060 | 4,760 |
80 | .086 | 4,140 |
100 | .115 | 3,780 |
120 | .150 | 3,470 |
140 | .191 | 3,110 |
Bullets, artillery projectiles, and rockets are launchedpoint on so that the factor A/M is minimal. Bullets and artilleryprojectiles are further essentially stabilized in this minimal presentationthrough a high rate of spin about the long axis imparted by the rifling in thegun barrel. Random missiles seldom have a spin about the axis of flight but aremore apt to whirl or tumble through the air. Retardation is more rapid becauseof the excessive area presented for the air to act upon.
Random fragments frequently have a shape conducive toexcessive retardation as compared with the ideal form. Here the function v/a alsoplays an important role. The ideal shape when a is greater than vis the so-called teardrop section with the round portion to the front. When vexceeds a, the ideal shape is a pointed form, ogival orparaboloidal in section with the point to the front. For minimal retardation,surfaces should be smooth. Random missiles from bombs, artillery, and rocketprojectiles are usually rough. Secondary missiles of sand and pebbles may bequite smooth and perhaps approach
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the teardrop so far as leading edge presentation isconcerned. Secondary missiles of glass may be quite pointed and are often likelyto fly point on because of the vane action of their surfaces. In glassfragments, A/M may be favorable, A being minimal forthe fragment and M fairly high considering the density of slightlymore than 2 for glass as compared to nearly 8 for steel and more than 11 forlead. The density of sand is similar to that of glass.
Fragments consistently have less mass than bullets, size forsize, owing to the approximately 50 percent greater density of lead as comparedwith that of steel, a representative fragment material.
Shell and rocket-projectile fragments are apt to be largerand consequently heavier than those from the usual general-purpose bomb and sohave a better sustained velocity. Special antipersonnel aerial bombs may beconstructed in such a fashion that fragments will be of a mass sufficient tosustain impact velocities at a level adequate to produce casualties at somedistance from the point of burst. Also, through selection of metal and design,there can be some control of fragment shape. An instance of shape control is thecorrugated casting used in the Mills hand grenade of World War I.
Ballistic shape.-The term "ballistic shape"as applied to missiles is employed to refer to those missiles specially designedto have the best possible exterior ballistic characteristics. In themissile-casualty field, the small arms bullet is probably the only missilefalling properly in this category because of shape and controlled flight throughspin imparted by rifling in the gun.
The effect of missile shape on retardation is strikingly shown in table 21which lists the remaining velocities at different distances from the point oforigin for fragments from a 4.5-inch HE shell and the Ml 150-grain bullet.Initial velocities are similar, approximately 2,800 f.p.s., in each case.
TABLE 21.-Retardation of effective fragments from an HEshell as compared with the M1 bullet
Distance from point of origin | Velocity of- | |
Effective shell fragment | M1 bullet | |
Feet | F.p.s. | F.p.s. |
0 | 2,800 | 2,800 |
50 | 1,560 | 2,710 |
100 | 1,360 | 2,645 |
150 | 1,150 | 2,580 |
200 | 1,020 | 2,525 |
300 | 890 | 2,440 |
400 | --- | 2,365 |
500 | --- | 2,300 |
Three major types of shape are encountered in military small arms missiles: Flat base with-rounded nose; flat base with pointed nose; and tapered orso-called boattail base with pointed nose.
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The first form is commonly used in sidearms, carbine, orother ammunition where velocities at battle ranges will be less than that ofsound in air. The second shape was developed in the first decade of the 20thcentury to improve the flight of military bullets when muzzle velocities weredeveloped to twice or more the velocity of sound in air. The taper-base bulletwas a later development to permit of greater mass and better flight when themoving bullet was retarded to or below the velocity of sound in air. At first,many observers considered the taper-base bullet to be more accurate, but itsaccuracy was found to be due, in all probability, more to necessary improvementsin manufacturing methods than to its shape alone. This bullet is slightly morestable in air flight because of the greater distance from center of gravity tocenter of pressure.
Careful analysis of bullets manufactured for matchcompetition has demonstrated that care in base design and production is moreimportant to accuracy than similar care regarding precision in the nose shape.
Theoretically, the bullet, or any projectile for thatmatter, to be accurate should be a perfect form of revolution with the center ofgravity in the axis of revolution. While this attainment is approximated,perfection is impossible, especially in a missile assembled of variousnonhomogeneous materials. Some asymmetry of mass distribution or shape or bothis the rule rather than the exception.
Futhermore, when a bullet passes through the gun bore inlaunching, there is an asymmetrical engraving by the lands of the rifling.Again in manufacture, bullets are usually pressed into form at pressures ofsomething less than 10 tons to the square inch. In firing, powder gas pressuresagainst the base of the bullet are usually of more than 20 tons to the squareinch. This results in deformation.
In the .30 caliber rifle barrel, the bore diameter is 0.300inch and the groove diameter 0.308 inch. Bullets made of a homogenous materialon a lathe and measuring 0.310 inch in diameter have been fired throughaccuracy barrels with a groove diameter of 0.308 inch and recovered afterfiring. On recovery, they still measured 0.310 inch in diameter, demonstratingeither gun barrel stretch or temporary compression of the bullet or both.
Considerable heat is developed by the friction of the bulletin passing through the gun bore, and the temperature of the powder gases ishigh (above that of molten steel). There is some evidence that the lead core ofbullets under certain conditions can be altered at least during the earlierportion of its flight. This permits some core deformation with consequentasymmetry of mass distribution.
Inherent and induced asymmetry in the bullet results in moreor less yaw (deviation of the longitudinal axis from the line offlight) in the bullet during flight. Yaw is an important factor in the physical considerationof the bullet-produced wound and will be discussed later in greater detail(p. 127).
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Mass
Table 22 shows the velocities of fragments of varying weight and randomshapesat several distances from the point of a bombburst and demonstrates clearlythe effect of mass (really the factor A/M) on impact velocities. Theinitial fragment velocity in all cases was 7,390 feet per second.
TABLE 22.- Effect of mass on the retardation of fragments
Distance from burst | Weight of fragment | Velocity | Retardation |
Feet | Ounces | F.p.s. | F.p.s. |
80 | 0.012 | 2,230 | 5,160 |
80 | .023 | 3,150 | 4,240 |
80 | .085 | 4,160 | 3,230 |
80 | .390 | 5,180 | 2,210 |
200 | .061 | 990 | 6,400 |
200 | .148 | 1,710 | 5,680 |
200 | .345 | 2,510 | 4,880 |
200 | 1.05 | 3,550 | 3,840 |
500 | .214 | 531 | 6,859 |
500 | 1.08 | 972 | 6,418 |
500 | 2.12 | 1,400 | 5,990 |
From this table, it is immediately apparent that atany given distance from the point of launching, initial velocities beingcomparable, the heavier missile will have the greater impact velocity. This followsfrom the retardation formula, retardation varying inversely as the mass.
Furthermore, the factor d2/M or A/M willconsistently decrease as M increases, presupposing the fragment to be ofthe same material. Mass increases as the third power, while the correspondingarea increases as the square. Doubling the size of a mass increases the weighteight times and the area four times in homologous shapes.
This principle underlay the development of thetaper-base bullet. For instance, the .30 caliber flat-base bullet weighs 150grains versus 172 grains for the taper-base bullet. Both haveessentially the same bearing in the gun rifling, barrel friction iscomparable, and gas check is equally efficient. In the German 7.92 mm.bullets, the weights are 154 grains for the flat-base versus 197 grains forthe corresponding taper-base bullet. Impact velocities at any given rangewith these bullets will vary almost as the weight ratio, that is, as 172: 150or 197: 154, if the bullets are launched with the same initial velocity.
Originally, the .30 caliber 172-grain taper-base bulletwas loaded in ammunition for a muzzle velocity of 2,700 f.p.s., the same as thatof the 150-grain flat-base bullet. For ballistic reasons, muzzle velocities weresubsequently reduced to approximately 2,640 f.p.s. Some personnel alsocomplained of recoil as being excessive and impairing marksmanship.
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In this connection, it is to be noted that the recoil of aweapon is a function of the relative masses of the gun and bullet and themuzzle velocity of the projectile. Any decreases in weight of gun, increasein weight or muzzle velocity of the bullet will increase the recoil.
The Germans launched their 197-grain taper-base bullet witha muzzle velocity of approximately 200 f.p.s. less than that used with the flatbase, 154-grain bullet (2,480 to 2,500 f.p.s.). The Japanese also launched their196.9-grain 7.7 mm. taper-base bullet at a fairly low velocity, 2,239feet per second.
Area of Presentation of Random Fragments
Theoretically, the area of presentation of a random fragmentmay be anything from a minimum (a) to a maximum (A) possiblefor any given fragment. However, mathematical investigation indicates that theaverage area of presentation in random fragments will be approximately 70percent of A.12
Explanation for this lies in the fact that, because of theasymmetry of form as well as the unequal application of the impelling forces,fragments commonly have whirling or tumbling motions in addition to themotion of translation. In general, the greater the area of presentation inrelation to the mass, the greater will be the retardation and the lower theimpact velocity.
Shape can affect area of presentation. A round ball, forinstance, has only one possible area. On the other hand, a rectangular objectmay have many possible areas of presentation from the minimum to the maximumsection possible.
Bullets and projectiles are designed to afford the minimum area of presentationcombined with the maximum possible mass. Minimum area of presentation ismaintained through the action of the spin about its longitudinal axis imparted to a projectile bythe riflingin the gun barrel. Rifling of a gun barrel was a major improvement accomplishedin the latter part of the 18th century.
Yaw
Yaw, deviation of the longitudinal axis from the line offlight, in a bullet without doubt plays a most important role in explainingmany of the anomalies encountered in the study of bullet wounds. Yaw isincreased proportionately to the relative densities of the retarding medium ascompared to air, so in tissues it is augmented some 800 times, with resultingvery complex, rapid bullet motions. This rapid, complex motion accounts forwound damage much more extensive than attributable to motion of translationalone. Yaw augments the retardation of a bullet in tissue, thereby materiallyincreasing the amount of kinetic energy entering into the wound production.
12Morse, H. M., Baldwin, R.,Kolchin, E.: Report on the Uniform Orientation and Related Hypotheses for BombFragments, With Applications to Retardation and Penetration Problems. Report No.T.D.B.S. 3, Office of Chief of Ordnance, Washington, D.C., 30 Jan. 1943.
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Yaw results from two factors: (1) Spin imparted by rifling;(2) imperfections in the bullet due to construction or deformation in the boreof the gun and imperfections in the gun.
To have a yaw, a bullet must have a length greater than itsdiameter. There can be no yaw in a round ball. In flight, the forces ofretardation can be resolved in a point within the moving object. In addition,there is within the solid the center of gravity and in the sphere the two pointscoincide, hence there is no lever between the two points about which anoverturning force can operate.
In the bullet, or cylinder, in flight in a point-onorientation, the point at which the opposing forces are resolved will bedifferent from the center of gravity. An overturning force will operate on thelever between these two points. Without spin, the bullet will tumble end overend.
With the muskets and smoothbore guns of the 17th and 18thcenturies, round balls were employed. Bore diameters of guns were larger than inmodern weapons, and powder pressures and velocities were comparatively low.
American hunters required accuracy and range. This naturallyled to smaller bore weapons and longer barrels which, while decreasing the massof the ball, resulted in increased velocities and range. As velocities areincreased with the round ball in a smoothbore barrel, accuracy is lost. The ballmay be quite erratic in flight. The idea of imparting spin to the missile bymeans of rifling naturally followed. This restored accuracy. It is now knownthat the inaccuracy of the ball is due to air piling up in front of it and thatspinning the ball prevents this accumulation of air. The cylindrical bulletgradually evolved during the 19th century, and rifle calibers declined withpowder improvement. The U.S. military weapon for some years was the Springfield.45-70, which fired a heavy lead bullet weighing more than 400 grains. Thiswas followed near the end of the 19th century by the Krag-Jorgesen rifle of .30caliber and a 220-grain jacketed bullet. In 1903, the Springfield magazine rifleof .30 caliber was adopted. At first, a rounded-nose bullet was used, but thiswas replaced in 1906 with the so-called spitzer bullet with an ogival headhaving the ogive struck with a radius of 7 diameters (calibers). This ogivalhead was developed in Germany early in the 20th century, and the first patentapplication in the United States was filed in 1905.
Most of this gradual change and improvement in bullets up tothe period of World War I was largely accomplished by rule-of-thumb orcrude scientific methods as judged by modern standards.
In the period of a little more than a century and a quarterfollowing 1775, the following changes in military weapons slowly evolved:
1. The rifled bore, putting spin on the bullet.
2. Gradual transition of the bullet from the round to theelongated shape.
3. Gradual change from a round nose to the sharp pointed,ogival, so-called spitzer nose.
During this transition, the pitch of the rifling wasgradually changed until most military weapons used a twist of approximately oneturn in a distance
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of 30 calibers.13 While it is customary to statethat the rifling makes a turn in so many inches, it is better to specify thepitch in calibers, which immediately permits of comparisons between weapons ofdiffering calibers.
Pitch of rifling through determining the rate of spin is afactor in controlling the stability of the bullet in flight and in turn thedegree of yaw on impact. The rate of spin in the usual military rifle is high.With the .30 caliber flat-base bullet at a muzzle velocity of 2,700 f.p.s. and arifling pitch of 30 calibers, the spin is more than 3,500 revolutions a second.This spin is only adequate to stabilize the 150-grain bullet in air flight. Thespin has a negligible effect in maintaining the bullet in a point-on position indenser mediums, such as water or tissues.
Spin maintains the bullet essentially in a point-on positionthrough its effect on what is known as the overturning couple. In the elongatedbullet, all retarding forces are resolved in a point somewhere in the axis ofthe bullet toward the nose. The center of gravity also will be in the axis butat a point nearer the base in the pointed-nose bullet. The distance betweenthese points is the overturning couple, or lever arm, through which the forcesresulting from the spin operate to stabilize the bullet.
Because a bullet is never a perfect form of revolution andbecause neither the center of pressure nor center of gravity is exactly in theaxis, there is always some degree of yaw or tip or gyroscopic precession. Owingto the gyroscopic action of the high rate of spin, this yaw goes through adefinite period which varies throughout the bullet's flight. Another factorinducing initial yaw is that, while the bullet passes through the gun barrel,the center of gravity is forced to travel in a circle so it will not be in theaxis of the bore, whereas, once the bullet is in free air flight, the rotationis about the center of gravity, which immediately takes over.
Length of bullet determines the relative location of thecenters of pressure and gravity and through that the length of the lever armthrough which the forces of spin operate. This makes the longer, taper-basebullet somewhat more stable than the usual flat-base form.
However, density of resistant materials is a direct factor onthe retardation and other motions of a missile. Water with a density 800 timesthat of air and tissues of slightly greater densities act much as a magnifyingglass, magnifying all of the retardations, yaw, and gyrations of the bullet 800or more times. A very slight tip or yaw will become one of more than 50? by thetime a .30 caliber 110-grain solid bullet homologous in shape with 150-grainflat-base bullet has traversed 3 inches of water. Not infrequently, the increasein yaw will exceed 100?. Changing from one density to another also inducesmarked variations in the degree of yaw.
This, of course, immediately changes the area ofpresentation; a bullet enters tissue point on but in a few inches may be tippedup to 90? or more and the
13The caliber of a weapon is the diameter of the borenot including the depth of the grooves. A unit of caliber is also used toexpress the length of an artillery weapon from breech face to muzzle and isequal to the diameter of the bore. For instance, many naval guns have a lengthof 50 calibers .-J.C.B.
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presentation area is its broadside. The forces of spin arestill operating, however, through the overturning couple and tend to stabilizeand maintain the bullet in point-on flight. Consequently, in another fewinches, the bullet is again point on and may leave the body through a small exitwound. Neither entrance nor exit wounds give any idea regarding the extensiveinterior destruction occasioned by the extreme tip and periodic bullet gyrationswithin the tissues.
While in flight, the bullet goes through all of the motionsof the spinning top, except that it is much quicker because of its higher rateof spin. Some conception of the rate of spin may be visualized when it isrealized that it is more than 100 times that of what is usually termed ahigh-speed electric motor armature which is rotating more than 1,700revolutions per minute. The MII bullet with a muzzle velocity of 2,800 f.p.s.spins at a rate of more than 200,000 revolutions per minute. The usual topspins at a few hundred turns a minute but is relatively better balanced than thebullet.
When a top is started spinning, it wobbles more or less in aperiodic manner. Then it stabilizes and, if well made, spins quite stably for anappreciable interval. Then, as it loses spin, it again becomes unstable andwobbles more and more as the spinning motion retards. The spinning bullet goesthrough similar gyrations while moving through the air. However, while thetop goes through its gyrations with its point as a fulcrum, the fulcrum aboutwhich the bullet's axis tips is the center of gravity of the bullet.
These varied motions are gyroscopic in nature and strictlyperiodic. At one instant, the bullet is point on, and at the next instant thebullet axis is at an angle to the line of flight. This angle of yaw increasesto a certain amount and then progressively decreases until it is again zero,when a node is reached and another similar gyration commences.
In air flight, degree of yaw is normally comparatively slight-less than 3? in properly designed military bullets.This spin issufficient to stabilize the bullet in an essentially point-on position. Thebullet goes through a complete gyration in a distance of 10 to 20 feet, at lessthan 0.001 second of time.
As the bullet leaves the muzzle of the gun, the actual angleof yaw is very small, only a few minutes of arc, but the angular velocity of yawis considerable so that as the bullet moves along its trajectory the yawincreases until it reaches a maximum at some 10 or 15 feet in front of themuzzle. From here, it then proceeds to yaw in an approximately periodic mannerthroughout the remainder of its flight.
The angular velocity of the yaw is usually due to one of thefollowing causes or a combination of them. It may be due to the fact that theaxis of the bullet makes an angle with the bore so that the axis of the bulletis moving in a cone around the axis of the bore. This conical motion providesfor the angular velocity just mentioned. Another cause is due to some asymmetryor inhomogeneity in the bullet which may result in the major axis of theellipsoid of inertia of the bullet having a different direction from the axis ofform. The result of this sort of angle is equivalent to the result produced whenthe axis of
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the bullet makes an angle with the axis of the bore. Thegyroscopic forces of spin quickly damp out the initial yaw so that at a distanceof a hundred yards or so the bullet is flying almost exactly nose on.14
Bullet spin is retarded less rapidly than the motion oftranslation. However, at long ranges, several thousand yards or more, the bulletpresentation is further complicated by the fact that the gyroscopic forces ofspin tend to maintain the bullet's axis parallel to the axis of the gunthroughout its flight. The axis of the bullet does not tend to follow thetrajectory except for a short distance from the gun. As an example, if a bulletis fired from a gun elevated at an angle of 30?, the axis of the bullet tendsto maintain this 30? angle throughout its flight. This results in asymmetry ofthe retarding air forces with respect to the bullet axis and consequentincrease in angle of yaw at extreme ranges as the axis of the trajectorydeviates from the direction of the axis of the gun bore.
Surgeons have often noted "key-hole" entrancewounds at extreme ranges and erroneously attributed them to "tumbling"bullets. In unimpeded air flight, a bullet given adequate initial spin seldom"tumbles" or flies end over end. Of course, a bullet often tumblesbadly after striking a glancing blow in ricochet. However, at extreme ranges, abullet seldom flies with its axis parallel to the ground, so often hits with itsaxis far from perpendicular to the surface struck. The entrance wound is usuallyan accurate record of the bullet's presentation at the instant of impact.
On entering a medium denser than air, all of these motions,especially the degree of yaw, are magnified. On entrance, yaw may be only afraction of a degree, but it is quickly increased by approximately the ratio ofthe medium densities which for water and tissues is some 800 times. Likewise,period of gyration or distance from node to node is correspondingly shortened. Abullet may be essentially point on at impact and in a space of 3 inches betipped in yaw at right angles to its line of flight and in another 3 inchesagain be essentially point on.
Moving from a medium of one density to that of anotherdensity influences the bullet's motions and can result in extreme angles ofyaw. For instance, moving from air to tissue, from soft tissue to bone, andagain from bone to soft tissue will have a profound influence in inducingextreme changes in the gyrations of the bullet and all of its motions, includingretardation.
Retardation for any bullet also varies as the square of theangle of yaw in degrees so that a yaw of 13? will double the retardation.15Letting δ be the angle of yaw indegrees, theretardation factor due to yaw is
1 + (2)/ (169)14Personal communication, R. H. Kent, Physicist,Aberdeen Proving Ground, Md., to Maj. R. W. French, 28 Mar. 1947.
15Kent, R. H.: The Theory of the Motion of a BulletAbout Its Center of Gravity in Dense Media, With Applications to Bullet Design.[An undated manuscript sent to Major French in the period 1931-32.]
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Table 23 gives the retardation factor for varying values of yaw.
Yaw | Yaw2 | Yaw2/169 | 1+Yaw2/169 |
Degree | Degree |
|
|
2 | 4 | 0.0236 | 1.02 |
4 | 16 | .0944 | 1.09 |
8 | 64 | .3776 | 1.38 |
16 | 256 | 1.5104 | 2.51 |
32 | 1,024 | 6.0416 | 7.04 |
64 | 4,096 | 24.1664 | 25.17 |
128 | 16,384 | 96.6656 | 97.67 |
Yaws of more than 170? have been observed in bullets inpassing through 6 inches of water. Theoretically, yaw can be of any value tojust under 180 degrees. A yaw of 170? increases the retardation factors 172times and a yaw of 179?, 190 times. This readily explains why a superspeedbullet is stopped in a very few feet of a homogeneous medium such as water.
This also explains why a supervelocity bullet is retarded sogreatly in producing a casualty. The extreme retardation of such bullets canresult in a wound with comparatively enormous destruction, tissue pulping, boneshattering, and other extreme manifestations only possible with the modern,fast-moving military bullet.
THE WOUND AS A PHYSICAL ENTITY
Permanent manifestation of the missile wound is a hemorrhagicarea surrounding the track of cut and torn tissue left in the missile wake.However, while cutting through the tissue, a missile also imparts radialvelocity to the tissue elements resulting in a development of a temporary cavityas the tissues absorb the kinetic energy lost by the missile throughretardation. In absorbing this energy, some tissues more elastic than othersreact in such a manner that this cavity goes through several pulsations, eachsuccessive temporary cavity being smaller in volume than the preceding cavity.In longitudinal section, the temporary cavity is a conic section, usually anoblate ellipsoid in the case of a missile without yaw or particular form factor,such as a sphere.
In producing a casualty, the missile is commonly moving inthe tissue a thousandth of a second or less, and the actual wound is producedtoo rapidly for human perception to appreciate all that goes on. As examples ofactual time intervals involved, the following two instances are cited,considering the thigh with a thickness of 8 inches to be the part injured:
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First, consider a bullet weighing 150 grains with an impactvelocity of 2,500 f.p.s. and a residual exit velocity of 1,500 f.p.s. It willtraverse the 8 inches of tissue and bone in 0.00033 second and expend 1,330ft.-lb. of energy during its passage through the thigh.
Second, the same bullet with an impact velocity of 2,000f.p.s. and an exit velocity of 1,000 f.p.s. will traverse the thigh in 0.00045second, and 998 ft.-lb. of kinetic energy will be absorbed in the wound.
On dissection by the military surgeon, the most prominentfeature of the wound will be the permanent cavity or wound track which on closeinspection is found to be surrounded by a zone of more or less damaged tissuesfilled with extravasated blood. Partially or completely disrupted nerves may befound along with damaged blood vessels, though, barring a direct hit by themissile, most of the larger veins will be intact and the arteries uninjured.Bone may be found to be fractured without evidence of a direct hit. Suchfractures are usually fairly simple, while those which result from a direct hitwill show more comminution, especially at the cited impact velocities.
Research with spheres16 asmissiles has demonstrated that both the volume of the permanent cavity and thetissue showing evidence of devitalization and extravasation of blood is afunction of the kinetic energy entering into the wound; also, that the volume ofthe tissue showing extravasation is 11.8 times the volume of the permanentcavity. It is anticipated that with bullets the degree of yaw will modify thedirect relationship between volume and impact energy or square of velocity.
Further research with steel spheres has demonstrated that,some 400 microseconds after impact, a temporary cavity some 26 times the volumeof the permanent cavity reaches its greatest diameter perpendicular to the pathof the missile. This cavity may go through several pulsations with correspondingnegative and positive pressure phases. All of these phenomena are too rapid tobe perceived by the human eye.
This temporary cavity and associated phenomena explain theso-called explosive effects often noted with high-velocity missiles. It accountsfor tissue pulping and other damage some distance outside of the permanentcavity or apparent bullet track. During the stretching of tissue concurrentwith the expansion of the temporary cavity, nerve trunks are often stretched tosuch a degree that function is destroyed without apparent gross injury.
Permanent Cavity
As the missile tears through the tissues, there are twoimmediate results: (1) The cutting or tearing of a permanent cavity along itstrack; and (2) the initiation of severe shock waves, with pressures of well over1,000 pounds to the square inch, which travel ahead of and out from the missileat the velocity of sound in the tissues, approximately 4,800 feet per second.
16For the complete report of this work, see pages 147-233.
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Experiment has demonstrated that for every foot pound ofenergy doing work in wound formation there will be a permanent cavity remainingwith a volume of 2.547 x 10-3 cubic inches. With the average military riflebullet and resultant wound, this presages a permanent cavity slightly larger inaverage diameter than the bullet. Yaw may modify the shape of the permanentcavity from point to point along the track, but the total volume should followthis expression as yaw also modifies the amount of energy doing work.
In the case of slow low-energy missiles, the permanentcavity will be distinctly smaller in diameter than the missile which producedit. Tissue elasticity accounts for the reduction in volume.
While the passage of the missile is responsible for thepermanent cavity, it actually comes into permanent being sometime after themissile's passage. As the bullet passes through the tissue, considerableradial motion is imparted to the tissue elements, and a large temporary cavityis formed. Slow-motion pictures and other experimental evidence show that there are several pulsations before the wound track becomes wholly quiescent.This again is probably due to tissue elasticity, particularly the restrainingaction of the skin as it absorbs the energy imparted to it by the missile.
Area of Extravasation
On dissection of the wound track, the adjacent tissue isfound to be quite sanguineous and, in the case of the average rifle-bulletwound, full of extravasated blood for an inch or more away from the track. Inthis region, histologic examination reveals a separation of muscle bundles with capillary hemorrhages into the interspaces.
In cross section of a wound track, this hemorrhagic areais found to be well defined. Experiment has shown that for every foot pounddoing work in producing the wound there will be 30.105 x 10-3 cubic inches ofthis hemorrhagic tissue.
Survival studies have suggested that much of the tissuein this area of extravasation will regenerate if it is kept clean. However, inthe battlefield, cleanliness is often impossible, and this pulped, hemorrhagic tissue provides an excellent pabulum for pyogenic bacteria andthe clostridia which are responsible for gas gangrene. Early, adequatedebridement is the indicated procedure in order to guard against secondaryinvaders and to insure early healing.
Temporary Cavity
Microsecond X-ray and high-speed motion picture studies havedemonstrated the formation of a temporary cavity with a volume almost 27 timeslarger than that of the permanent cavity. This cavity reaches its greatestsize after the impact of the missile and after it has entirely left thewound track. Its maximum volume is 66.247 x 10-3 cubicinches for each footpound doing work in producing the wound.
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In the first hypothetical thigh wound (p. 133) in which 1,330ft.-lb. of energy were expended, the temporary cavity would have a maximumdiameter of perhaps 12 or 15 inches, depending on the presentation of thebullet. Its total volume would be 88.1 cubic inches.
This temporary cavity, long suspected but never beforeperceived in tissue, is the logical sequence to the passage of a missile throughan elastic medium. Tissues are known to be quite elastic. The pulsationlikewise is to be expected in some tissues, such as muscle, as would occur whena ball suspended by a rubber band is dropped. However, the pulsations damp outrapidly, and the human senses are only able to perceive that there has been somegeneral disturbance of the tissues.
Shape of the temporary cavity is a function of the shapeand presentation of the missile. With a sphere, the shape of the cavity isquite symmetrical-a conic section of revolution, fusiform in longitudinalsection. In the case of a fragment, it may be quite asymmetrical as thepresentation of the irregular fragment varies. In the case of the bullet, yawwill result in asymmetry. In fact, where the bullet goes through a node andthen again into yaw, there may be several larger temporary fusiform cavitiesconnected by much smaller ones, the so-called scalloped wound remaining in thepermanent cavity. Variations in tissue also affect the type and shape ofcavity.
This cavity is the result of particles set into motion by thepassage of the bullet. Time is required to overcome their inertia, hence thelag in full development of the temporary cavity as compared to the passage ofthe bullet. While the missile imparts outward moving forces to theparticles at the instant of its passage, it requires some microseconds for theparticles to move outward to their greatest distance and for the physicalproperties of the tissues to absorb the forces involved. Average particlevelocities are not particularly great. In the hypothetical thigh shot, theywould be 125 feet per second.
While foot pounds, units of energy, have been used indiscussing the mechanics of the missile wound, a better conception of themagnitude of the forces involved may come from a consideration of the powerutilized in wound formation. Power is the measure of work done by the energyexpended by the missile in the wound. The 1,330 ft.-lb. absorbed in 0.00033second in the first hypothetical wound is the equivalent of some 7,200horsepower of work. In the second wound (p. 133) with 998 ft.-lb. absorbed in0.00045 second, the work equivalent is more than 4,100 horsepower. Work donein any missile wound will seldom be less than several hundred horsepower andwill often considerably exceed the figures cited. The larger numerical valuesof horsepower can be expected when it is realized that 1 horsepower is thelifting of 550 pounds for 1 foot in 1 second. In the wound, more than 1,000ft.-lb. of energy may do its work in much less than one-half of a thousandthof a second.
With this realization of the forces involved in theproduction of the missile casualty, some of the otherwise anomalousmanifestations in the wound appear much more logical. For instance, fracturesoccur at some distance from the
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missile track and without any direct contact between the boneand the missile. Forces may be transmitted through the essentiallynoncompressible blood and rupture a vein some distance from the missile'spath. Nerves may be paralyzed and yet fail to show gross evidence of physicaldamage. In some wounds in muscle, splitting along fascial planes will be notedfor a considerable distance from the path of the bullet.
Fluid-filled viscera are often blown asunder by the operationof hydraulic forces. High-velocity missiles may pulp the brain substance. Insome cases, the bones of the skull are separated along the suture lines asthough an explosion has occurred within the brain case. This is but anothermanifestation of the forces operating in the formation of the temporary cavity,and examination often reveals clean holes of entrance and exit of the missileshowing that the bony rupture occurred after its passage. Similarly, in shootingthrough a can filled with water, the rupture of the can occurs after thethrough-and-through passage of the bullet.
Knowing the relationship between the permanent cavity, zoneof extravasation, and temporary cavity, the military surgeon can make use ofthis knowledge in determining the extent of the wound. The zone of extravasationis readily seen and can indicate the total involvement. For instance, if an areaof tissue full of extravasated blood is seen extending for a distance of 2inches from the axis of the permanent cavity, it is known that damage alongfascial planes, perhaps some blood vessel rupture, and some nerve injury can beexpected to a further distance of some 2? inches beyond the zone ofextravasation. If note is made of the extent of extravasation, some idea as tothe amount of energy expended in the wound is determinate.
The military surgeon should never be misled, especially inthe case of bullets, by small entrance and exit wounds. These small skinopenings may be no indication whatever of the possible extent of the internalwound. This is particularly true of the yawing bullet and may be true of thehigh-velocity, spinning fragment. Elasticity of the skin often results in almostcomplete closure of skin wounds.
Temporary Cavity Pulsations
In water and certain tissues, such as the muscular thighsurrounded by highly elastic skin, the temporary cavity goes through a series ofpulsations. As the cavity expands, a negative, subatmospheric gage pressuredevelops within the tissues. This is followed by a positive pressure of greaterintensity but of shorter duration with the collapse of the cavity. In water,these pulsations may continue for as many as seven or eight cycles, disappearingas the cavity disintegrates. While measurements of tissue phenomena have notbeen made as complete as those in water, definite indications are that thetissue often behaves in a manner wholly analogous to water. There may be two ormore pulsations.
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For water, the period of the pulsations is related to theamount of energy doing work. The time of a cycle in seconds is equal to 2.35 x10-3 times the cube root of the foot pounds of energy absorbed. Thisrelationship also is reasonably applicable to most tissue wounds. The followingtabulation gives the computed time of a complete pulsation in milliseconds forvarying amounts of energy in foot pounds:
Energy (ft.-lb.): | Duration of pulsation (milliseconds) |
250 | 15 |
500 | 19 |
1,000 | 23 |
1,500 | 27 |
2,000 | 30 |
Coupled with the temporary cavity in water and its pulsationsthere are internal pressure changes. When the cavity is fully expanded,pressures in the medium are at their lowest value, often a full atmosphere ormore subnormal. As the temporary cavity decreases in size, pressures increasereaching a maximum value of three or four times atmospheric pressure.Oscillograms reveal that, while the positive pressures are greater in intensity,the duration of the negative pressure phase is twice as long.
While the initial shock wave shows very high pressures (1,000pounds per square inch and more), oscillograms show its duration to be short, 15to 25 microseconds. Available evidence indicates that this short duration mayexplain the apparent fact that little if any true tissue damage in gas-freetissues can be attributed to this initial shock wave despite its intensity.Other studies have shown that tissue elements withstand much higher staticpressures without damage.17 However, when gas is present in thetissue, damage often occurs.
Experimental studies afford quite conclusive evidence thatsubatmospheric pressures connected with cavity behavior are responsible for muchtissue destruction.
Though cavity pulsation has been detected in water, ingelatin block and in some tissues, in abdominal shots in the cat, no pulsationswere noted in microsecond X-rays. Here, a single temporary cavity followed byrapid collapse appears to be the rule. However, extensive damage to theintestines occurred which was due largely to the expansion of gas in theintestines in the subatmospheric pressures during the expansion of the temporarycavity and following the shock wave. This expansion of gas results in greatstretching of tissues and consequent rupture or other severe damage. Thisstretching is not due directly to either the shock wave or cavity formationbehind the missile but rather to the expansion of the air pocket already presentwithin the tissues. This air responds to the pressure changes around thetemporary cavity, and the stretching occurs as the result of the subatmosphericpressures when the included air expands.
17(1) Brown, D.E.S.: Effects of Rapid Compression UponEvents in Isometric Contraction of Skeletal Muscle. J. Cell. & Comp. Physiol.8: 141-157, 1936. (2) Cattell, M.: The Physiological Effects of Pressure.Biological Rev. of Cambridge 11: 441-476, 1936.
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Though not established experimentally, it is anticipated thatthe subatmospheric pressures may likewise lead to sudden expansion of gas in thealveoli in the lungs so as to stretch the walls and rupture small blood vessels.Such injury is indicated from field observations.
The extent of the temporary cavity formation and therelationship of tissue damage to the permanent wound track may be influenced byconstricting clothing, tenseness of muscles, or other variables at the time ofwounding. For instance, removing the skin from a cat's leg before woundingresulted in a larger temporary cavity with more of a wound "blow-out."On the other hand, reinforcing the skin with Scotch tape changed the shape ofthe cavity and resulted in tissue damage to a greater distance from the missiletrack. Elasticity of the skin and muscle fibers appeared to play a considerablepart in predetermining the physical nature of the missile wound.
Skin Penetration and Energy Absorption18
Skin and bone both appeared from experimental data to offer aparticular resistance to penetration differing from other tissues. There was acritical velocity in each case below which a missile would not effectpenetration. There was comparatively little difference in the value of thiscritical velocity irrespective of the size of the missile.
Initial velocity required for a 4/32-inch steel sphere weighing2 grains was found to be 170 f.p.s. for penetration of human skin. Lead sphereshaving an 11/64-inch diameter, weighing approximately 7 grains with avelocity of 161 f.p.s., did not effect penetration. Even extremely largemissiles will lose about 125 f.p.s. of their impact velocity in penetrating thesurface of the skin. Area of presentation affects skin penetration to suchdegree that the loss in velocity is proportional to the reciprocal of thediameter of the spheres.
Skin was found to be more resistant than other tissues. Thedrag coefficient, a value dependent on the resistance encountered by a missileand independent of the missile, for human skin was 0.528 as compared to 0.297for water. The coefficient for cat muscle was 0.448 and for 20 percent gelatinblock, 0.350. Human skin had a drag coefficient more than 20 percent greaterthan cat muscle. While the drag coefficient was not determined, indications werethat cat skin was slightly more resistant to penetration than human skin.
The skin resistance offered a logical explanation for thefact that shrapnel, formerly used as an antipersonnel agent, was commonlyineffective. It was usually employed at such ranges that remaining projectilevelocity was low. The bursting charge propelling the shrapnel balls was commonlyincapable of imparting sufficient velocity to effect skin penetration. Shrapnelballs also had a poor ballistic shape and were rapidly retarded in air flight.
18Grundfest, H., Korr, I. M.,McMillen, J. H., and Butler, E. G.: Ballistics of the Penetration of Human Skinby Small Spheres. National Research Council, Division of Medical Sciences,Office of Research and Development, Missile Casualties Report No. 11, 6 July1945.
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An anomaly in skin penetration was the threshold velocitynecessary to effect penetration, rather than a certain amount of energy. A2-grain sphere required a velocity of 170 f.p.s. for penetration or a negligibleamount of energy when measured in foot pounds. For a 150-grain bullet topenetrate skin, a velocity of approximately 125-150 f.p.s. was requiredcorresponding to approximately 5 ft.-lb. of energy. The 2-grain sphere wouldhave less than one-fiftieth this amount of energy.
Bone Penetration19
Bone offered a situation similar to that found in skin. Herea minimal velocity of approximately 200 f.p.s. was necessary to effectpenetration. Once penetration had been effected, any velocity remaining abovethe 200 f.p.s. would operate to effect deeper penetration in direct proportionto the square of the velocity and the sectional density of the missile.Penetration and damage to bone was effectively gaged by the amount of energyperforming work, essentially proportional to the square of the velocity.
While specific experiments were conducted with beef bone,results are substantiated by other work with human and horse cadavers. Resultswere essentially the same.
In conjunction with these critical velocities necessary toeffect penetration, some consideration should be given to the .45 caliberautomatic pistol and its load. From time to time, complaint has been registeredthat this weapon is not as efficient under all conditions as could be desired ina self-defense weapon. A 234-grain full metal patch bullet is used, and it islaunched with a muzzle velocity of 825 feet per second. Following is atabulation of the kinetic energy available with this bullet at variousvelocities:
Velocity (f.p.s.): | Kinetic energy (ft.-lb.) |
825 | 383 |
700 | 254 |
600 | 187 |
500 | 130 |
400 | 83 |
300 | 47 |
Considering the 125 f.p.s. required to effect skinpenetration, it can be seen that the remaining velocity and energy are droppeddown to at least 700 f.p.s. and 254 ft.-lb., respectively. The penetration of bonerequires another 200 f.p.s. and dropping remaining velocity to 500 f.p.s. andenergy to 130 ft.-lb. In addition to these losses, passage through tissueresults in some retardation, so remaining velocity and energy will certainly besomething less than the figures cited. Furthermore, impact seldom occurs atpointblank ranges, and
19Grundfest, H.: Penetration of Steel SpheresIntoBone. National Research Council, Division of Medical Sciences Office ofResearch and Development. Missiles Casualty Report No. 10, 20 July 1945.
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the initial velocity is certain to be something less than825 f.p.s. when the bullet hits the skin.
From an analysis of these facts and the requirements forpenetration of skin and bone, it can be readily appreciated that the .45 caliberbullet is of little value as a wound-producing agent except in the softertissues and at near ranges. The bullet often fails either to penetrate or tofracture bone and practically never shatters bone in the manner common to therifle bullet or fragment. The Japanese and German sidearms with muzzlevelocities of approximately 1,100 f.p.s. were much more effective asantipersonnel weapons than the .45 caliber weapon. While the same bullet withits characteristics was used in the submachinegun, multiple hits probablycompensated for the weaknesses, so apparent in single shots.
Of course, the carbine with its much higher muzzle velocityhas largely replaced the .45 automatic pistol and is a more effectiveantipersonnel weapon than any of the sidearms.
Histologic Character of Tissue Damage
Muscle damage is evidenced by swelling and coagulation ina region a few millimeters from the permanent cavity of the wound. Often, nomuscle damage is noted in regions where blood extravasation from rupturedcapillaries is pronounced.
Expansion of the temporary cavity along fascial planesresults in an accumulation of blood from the rupture of small blood vessels, butthe larger vessels are remarkably resistant to injury, probably because of theirelasticity. Sometimes, a blood vessel is left spanning a permanent cavity. Inother cases, nerves are severed, while blood vessels running parallel with thenerve in the same fascia are intact. Veins with their comparatively thin wallsoften rupture as the result of transmitted forces, while arteries with theirmore resistant walls are usually patent barring a direct hit.
Cavity Formation by the Moving Missile
As a function of the amount of kinetic energy doing work, thespeeding missile results in a permanent cavity, a zone of tissue full ofextravasated blood, and a temporary cavity in tissue. In water, it also producesa cavity. The volumes of the various cavities in cubic inches are related to thefoot pounds of energy expended by the following formulas:
In tissue:
Permanent cavity-2.547 X 10-3 ft.-lb.
Zone of extravasation-30.105 X 10-3 ft.-lb.
Temporary cavity-66.247 X 10-3 ft.-lb.
In water:
Temporary cavity-737.7 X 10-3 ft.-lb.
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Table 24 shows the comparative volumes of the various cavities in cubicinches for varying amounts of energy expended.
Energy | Cavity in tissue (in cubic inches) | Cavity in water (cubic inches) | ||
Permanent | Zone of extravasation | Temporary | ||
| F.p.s. |
|
|
|
|
250 | 0.63 | 7.53 | 16.57 | 184 |
500 | 1.27 | 15.05 | 33.13 | 369 |
1,000 | 2.55 | 30.11 | 66.25 | 738 |
1,500 | 3.82 | 45.16 | 99.37 | 1,107 |
2,000 | 5.09 | 60.21 | 132.49 | 1,476 |
2,500 | 6.36 | 75.26 | 165.61 | 1,845 |
3,000 | 7.63 | 90.31 | 198.73 | 2,214 |
3,500 | 8.91 | 105.37 | 231.86 | 2,583 |
