Shrapnel shell

The size of shrapnel balls in World War I was based on two considerations. One was the premise that a projectile energy of about 60 foot-pounds force (81 J) was required to disable an enemy soldier.[7][8] A typical World War I 3-inch (76 mm) 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 170 grains (11 g), or 41-42 balls = 1 pound.[note 1] Hence this was a typical field gun shrapnel bullet size.

The maximum possible range, typically beyond 7,000 yards (6,400 m), 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 3,000 yards (2,700 m), 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.

${\displaystyle 1/41\times 1050^{2}/64.32=418{\text{ foot-pounds}}}$

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 1,500 yards (1,400 m) to 3,000 yards (2,700 m) 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.

Trajectory and pattern of US 3-inch (76 mm) Shrapnel shell of WWI era.

The other factor was the trajectory. The shrapnel bullets were typically lethal for about 300 yards (270 m) from normal field guns after bursting and over 400 yards (370 m) 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.[9]

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, fuzes and central tubes. Troops under a shrapnel barrage would attempt to convey any of these intact fuzes they found to their own artillery units, as the time setting on the fuze 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.

A firsthand description of successful British deployment of shrapnel in a defensive barrage during the Third Battle of Ypres, 1917:

... the air is full of yellow spurts of smoke that burst about 30 feet up and shoot towards the earth - just ahead of each of these yellow puffs the earth rises in a lashed-up cloud - shrapnel - and how beautifully placed - long sweeps of it fly along that slope lashing up a good 200 yards of earth at each burst.[10]

A sectioned British World War I 18 pounder shrapnel round (top) and complete round (bottom) displayed at the Canadian War Museum, Ottawa.
The spherical bullets are visible in the sectioned shell (top left), and the cordite propellant in the brass cartridge is simulated by a bundle of cut string (top right). The nose fuze is not present in the sectioned round at top but is present in the complete round below. The tube through the centre of the shell is visible, which conveyed the ignition flash from the fuze to the small gunpowder charge in the cavity visible here in the base of the shell. This gunpowder charge then exploded and propelled the bullets out of the shell body through the nose.

During the initial stages of World War I, shrapnel was widely used by all sides as an anti-personnel weapon. It was the only type of shell available for British field guns (13-pounder, 15 pounder and 18-pounder) until October 1914. Shrapnel was effective against troops in the open, particularly massed infantry (advancing or withdrawing). However, the onset of trench warfare from late 1914 led to most armies decreasing their use of shrapnel in favour of high-explosive. Britain continued to use a high percentage of shrapnel shells. New tactical roles included cutting barbed wire and providing "creeping barrages" to both screen its own attacking troops and suppressing the enemy defenders to prevent them from shooting at their attackers.

In a creeping barrage fire was 'lifted' from one 'line' to the next as the attackers advanced. These lines were typically 100 yards (91 m) apart and the lifts were typically 4 minutes apart. Lifting meant that time fuzes settings had to be changed. The attackers tried to keep as close as possible (as little as 25 yards sometimes) to the bursting shrapnel so as to be on top of the enemy trenches when fire lifted beyond them, and before the enemy could get back to their parapets.

While shrapnel made no impression on trenches and other earthworks, it remained the favoured weapon of the British (at least) to support their infantry assaults by suppressing the enemy infantry and preventing them from manning their trench parapets. This was called 'neutralization' and by the second half of 1915 had become the primary task of artillery supporting an attack. Shrapnel was less hazardous to the assaulting British infantry than high explosives - as long as their own shrapnel burst above or ahead of them, attackers were safe from its effects, whereas high-explosive shells bursting short are potentially lethal within 100 yards or more in any direction. Shrapnel was also useful against counter-attacks, working parties and any other troops in the open.

British Expeditionary Force "GHQ Artillery Notes No. 5 Wire-cutting" was issued in June 1916. It prescribed the use of shrapnel for wirecutting, with HE used to scatter the posts and wire when cut. However, there were constraints: the best ranges for 18-pdrs were 1,800–2,400 yards. Shorter ranges meant the flat trajectories might not clear the firers' own parapets, and fuzes could not be set for less than 1,000 yards. The guns had to be overhauled by artificers and carefully calibrated. Furthermore, they needed good platforms with trail and wheels anchored with sandbags, and an observing officer had to monitor the effects on the wire continuously and make any necessary adjustments to range and fuze settings. These instructions were repeated in "GHQ Artillery Notes No. 3 Artillery in Offensive Operations", issued in February 1917 with added detail including the amount of ammunition required per yard of wire frontage. The use of shrapnel for wire-cutting was also highlighted in RA "Training Memoranda No. 2 1939".

Shrapnel provided a useful "screening" effect from the smoke of the black-powder bursting charges when the British used it in "creeping barrages".

One of the key factors that contributed to the heavy casualties sustained by the British at the Battle of the Somme was the perceived belief that shrapnel would be effective at cutting the barbed wire entanglements in no man's land (although it has been suggested that the reason for the use of shrapnel as a wire-cutter at the Somme was because Britain lacked the capacity to manufacture enough HE shell[11]). This perception was reinforced by the successful deployment of shrapnel shells against Germany's barbed wire entanglements in the 1915 Battle of Neuve Chapelle, but the Germans thickened their barbed wire strands after that battle. As a result, shrapnel was later only effective in killing enemy personnel; even if the conditions were correct, with the angle of descent being flat to maximise the number of bullets going through the entanglements, the probability of a shrapnel ball hitting a thin line of barbed wire and successfully cutting it was extremely low. The bullets also had limited destructive effect and were stopped by sandbags, so troops behind protection or in bunkers were generally safe. Additionally, steel helmets, including both the German Stahlhelm and the British Brodie helmet, could resist Shrapnel bullets and protect the wearer from head injury:

... suddenly, with a great clanging thud, I was hit on the forehead and knocked flying onto the floor of the trench... a shrapnel bullet had hit my helmet with great violence, without piercing it, but sufficiently hard to dent it. If I had, as had been usual up until a few days previously, been wearing a cap, then the Regiment would have had one more man killed.[12]

A shrapnel shell was more expensive than a high-explosive one and required higher grade steel for the shell body. They were also harder to use correctly because getting the correct fuze running time was critical in order to burst the shell in the right place. This required considerable skill by the observation officer when engaging moving targets.

An added complication was that the actual fuze running time was affected by the meteorological conditions, with the variation in gun muzzle velocity being an added complication. However, the British used fuze indicators at each gun that determined the correct fuze running time (length) corrected for muzzle velocity.

With the advent of relatively insensitive high explosives which could be used as the filling for shells, it was found that the casing of a properly designed high-explosive shell fragmented effectively . For example, the detonation of an average 105 mm shell produces several thousand high-velocity (1,000 to 1,500 m/s) fragments, a lethal (at very close range) blast overpressure and, if a surface or sub-surface burst, a useful cratering and anti-materiel effect — all in a munition much less complex than the later versions of the shrapnel shell. However, this fragmentation was often lost when shells penetrated soft ground, and because some fragments went in all directions it was a hazard to assaulting troops.

One item of note is the "universal shell", a type of field gun shell developed by Krupp of Germany in the early 1900s. This shell could function as either a shrapnel shell or high explosive projectile. The shell had a modified fuze, and, instead of resin as the packing between the shrapnel balls, TNT was used. When a timed fuze was set the shell functioned as a shrapnel round, ejecting the balls and igniting (not detonating) the TNT, giving a visible puff of black smoke. When allowed to impact, the TNT filling would detonate, becoming a high-explosive shell with a very large amount of low-velocity fragmentation and a milder blast. Due to its complexity it was dropped in favour of a simple high-explosive shell.

During World War I the UK also used shrapnel pattern shells to carry "pots" instead of "bullets". These were incendiary shells with seven pots[13] using a thermite compound.

When World War I began the United States also had what it referred to as the "Ehrhardt high-explosive shrapnel" in its inventory.[14] It appears to be similar to the German design, with bullets embedded in TNT rather than resin, together with a quantity of explosive in the shell nose. Douglas Hamilton mentions this shell type in passing, as "not as common as other types" in his comprehensive treatises on manufacturing shrapnel[15] and high explosive shells[16] of 1915 and 1916, but gives no manufacturing details. Nor does Ethan Viall in 1917.[17] Hence the US appears to have ceased its manufacture early in the war, presumably based on the experience of other combatants.