Shrapnel shells were anti-personnel artillery munitions that carried many individual bullets close to a target area and then ejected them to allow them to continue along the shell's trajectory and strike targets individually. They relied almost entirely on the shell's velocity for their lethality.
The munition has been obsolete since the end of World War I for anti-personnel use, as High-explosive shells superseded it for that role. The functioning and principles behind shrapnel shells are fundamentally different from high-explosive shell fragmentation.
Shrapnel is named after Lieutenant-General Henry Shrapnel, a Royal Artillery officer, whose experiments, initially conducted on his own time and at his own expense, culminated in the design and development of a new type of artillery shell.
Usage of the term "shrapnel" has changed over time to also refer to fragmentation of the casing of shells and bombs, which is its most common modern usage and strays from the original meaning.
Development
In 1784, Lieutenant Henry Shrapnel of the British Army's Royal Artillery began developing an anti-personnel weapon. At the time, artillery could use "canister shot" to defend themselves from infantry or cavalry attack, which involved loading a tin or canvas container filled with small iron or lead balls instead of the usual cannonball. When fired, the container burst open during passage through the bore or at the muzzle, giving the effect of an oversized shotgun shell. At ranges of up to 300 m canister shot was still highly lethal, though at this range the shots’ density was much lower, making a hit on a human body less likely. At longer ranges, solid shot or the common shell—a hollow cast-iron sphere filled with black powder—was used, although with more of a concussive than a fragmentation effect, as the pieces of the shell were very large and sparse in number.
Shrapnel's innovation was to combine the multi-projectile shotgun effect of canister shot, with a time fuze to open the canister and disperse the shot it contained at some distance along the canister's trajectory from the gun. His shell was a hollow cast-iron sphere filled with a mixture of balls (“shot”) and powder, with a crude time fuze. If the fuze was set correctly then the shell would break open, either in front of or above the intended human objective, releasing its contents (of musket balls). The shrapnel balls would carry on with the "remaining velocity" of the shell. In addition to a denser pattern of musket balls, the retained velocity could be higher as well, since the shrapnel shell as a whole would likely have a higher ballistic coefficient than the individual musket balls (see external ballistics).
The explosive charge in the shell was to be just enough to break the casing rather than scatter the shot in all directions. As such his invention increased the effective range of canister shot from to about .
He called his device 'spherical case shot', but in time it came to be called after him; a nomenclature formalised in 1852 by the British Government.
Initial designs suffered from the potentially-catastrophic problem that friction between the shot and black powder during the high acceleration down the gun bore could sometimes cause premature ignition of the powder. Various solutions were tried with limited, if any, success. However, in 1852, Colonel Boxer proposed using a diaphragm to separate the bullets from the bursting charge, which proved successful and was adopted the following year. As a buffer to prevent lead shot deforming, a resin was used as a packing material between the shot. A useful side effect of using the resin was that the combustion also gave a visual reference upon the shell bursting, as the resin shattered into a cloud of dust.
British artillery adoption
It took until 1803 for the British artillery to adopt (albeit with great enthusiasm) the shrapnel shell (as "spherical case"). Henry Shrapnel was promoted to major in the same year. The first recorded use of shrapnel by the British was in 1804 against Batavian forces at Fort Nieuw-Amsterdam during the invasion of Surinam.Hogg p. 180. The Duke of Wellington's armies used it from 1808 in the Peninsular War and at the Battle of Waterloo, and he wrote admiringly of its effectiveness.
The design was improved by Captain E. M. Boxer of the Royal Arsenal around 1852 and crossed over when cylindrical shells for rifled guns were introduced. Lieutenant-Colonel Boxer adapted his design in 1864Marshall, 1920. to produce shrapnel shells for the new rifled muzzle-loader (RML) guns: the walls were of thick cast iron, but the gunpowder charge was now in the shell base with a tube running through the centre of the shell to convey the ignition flash from the time fuse in the nose to the gunpowder charge in the base. The powder charge both shattered the cast iron shell wall and liberated the bullets. The broken shell wall continued mainly forward but had little destructive effect. The system had major limitations: the thickness of the iron shell walls limited the available carrying capacity for bullets but provided little destructive capability, and the tube through the centre similarly reduced available space for bullets."Treatise on Ammunition", 4th Edition 1887, pp. 203–205.
In the 1870s, William Armstrong provided a design with the bursting charge in the head and the shell wall made of steel and hence much thinner than previous cast-iron shrapnel shell walls. While the thinner shell wall and absence of a central tube allowed the shell to carry far more bullets, it had the disadvantage that the bursting charge separated the bullets from the shell casing by firing the case forward and at the same time slowing the bullets down as they were ejected through the base of the shell casing, rather than increasing their velocity. Britain adopted this solution for several smaller calibres (below 6-inch) but by World War I few if any such shells remained.
The final shrapnel shell design, adopted in the 1880s, bore little similarity to Henry Shrapnel's original design other than its spherical bullets and time fuse. It used a much thinner forged steel shell case with a timer fuse in the nose and a tube running through the centre to convey the ignition flash to a gunpowder bursting charge in the shell base. The use of steel allowed a thinner shell wall, allowing space for many more bullets. It also withstood the force of the powder charge without shattering so that the bullets were fired forward out of the shell case with increased velocity, much like a shotgun. The design came to be adopted by all countries and was in standard use when World War I began in 1914. During the 1880s, when both the old cast-iron and modern forged-steel shrapnel shell designs were in British service, British ordnance manuals referred to the older cast-iron design as "Boxer shrapnel", apparently to differentiate it from the modern steel design."The action of Boxer-shrapnel is well known. The fuse fires the primer, which conveys the flash down the pipe to the bursting charge, the explosion of which breaks up the shell, and liberates the balls". Treatise on Ammunition 1887, p. 216.
The modern thin-walled forged-steel design made feasible shrapnel shells for howitzers, which had a much lower velocity than field guns, by using a larger gunpowder charge to accelerate the bullets forward on bursting.Treatise on Ammunition 1887, p. 205. The ideal shrapnel design would have had a timer fuse in the shell base to avoid the need for a central tube, but that was not technically feasible because of the need for manually adjust the fuse before firing and was in any case rejected from an early date by the British because of risk of premature ignition and irregular action.
World War I era
Technical considerations The size of shrapnel balls in World War I was based on two considerations. One was the premise that a projectile energy of about was required to disable an enemy soldier.Lt-Col. Ormond M Lissak, Ordnance and Gunnery. A Text-Book. New York: John Wiley, 1915. Page 446Treatise on Ammunition, 10th Edition, 1915. War Office, UK. Page 173. A typical World War I field gun shell at its maximum possible range traveling at a velocity of 250 feet/second, plus the additional velocity from the shrapnel bursting charge (about 150 feet per second), would give individual shrapnel bullets a velocity of 400 feet per second and an energy of 60 foot-pounds (81 joules): this was the minimum energy of a single half-inch lead-antimony ball of approximately , or 41–42 balls = 1 pound.Foot-pounds are calculated as wv2/2gc, where gc is the local acceleration of gravity, or 32.16 ft/second. Hence for the British calculation: 60 foot-pounds = 1/41 × v2/64.32 . Hence v2 = 60 × 64.32 × 41 . Hence v = 398 feet/second Hence this was a typical field gun shrapnel bullet size.
The maximum possible range, typically beyond , was beyond useful shrapnel combat ranges for normal field guns due to loss of accuracy and the fact that at extreme range the projectiles descended relatively steeply and hence the "cone" of bullets covered a relatively small area.
At a more typical combat range of , giving a fairly flat trajectory and hence a long "beaten zone" for the bullets, a typical 3-inch or 75-mm field gun shrapnel shell would have a velocity of approximately 900 feet/second. The bursting charge would add a possible 150 feet/second, giving a bullet velocity of 1,050 feet/second. This would give each bullet approximately 418 foot-pounds: seven times the assumed energy required to disable a man.
For larger guns which had lower velocities, correspondingly larger balls were used so that each individual ball carried enough energy to be lethal.
Most engagements using guns in this size range used direct fire at enemy from to distant, at which ranges the residual shell velocity was correspondingly higher, as in the table – at least in the earlier stages of World War 1.
The other factor was the trajectory. The shrapnel bullets were typically lethal for about from normal field guns after bursting and over from heavy field guns. To make maximum use of these distances a flat-trajectory and hence high-velocity gun was required. The pattern in Europe was that the armies with higher-velocity guns tended to use heavier bullets because they could afford to have fewer bullets per shell.Bethel p. 124.
The important points to note about shrapnel shells and bullets in their final stage of development in World War I are: They used the property of carrying power, whereby if two projectiles are fired with the same velocity, then the heavier one goes farther. Bullets packed into a heavier carrier shell went farther than they would individually. The shell body itself was not designed to be lethal: its sole function was to transport the bullets close to the target, and it fell to the ground intact after the bullets were released. A battlefield where a shrapnel barrage had been fired was afterwards typically littered with intact empty shell bodies, fuses and central tubes. Troops under a shrapnel barrage would attempt to convey any of these intact fuses they found to their own artillery units, as the time setting on the fuse could be used to calculate the shell's range and hence identify the firing gun's position, allowing it to be targeted in a counter-barrage. They depended almost entirely on the shell's velocity for their lethality: there was no lateral explosive effect.