Fragmentation (weaponry)

Fragmentation is the process by which the casing of an artillery shell, bomb, grenade, etc. is shattered by the detonation of the explosive core. The correct technical terminology of these pieces is "fragmentation" (sometimes shortened to frag) – although "shards" or "splinters" can be used for non-preformed fragments. Preformed fragments can be of various shapes (spheres, cubes, rods, etc.) and size and are normally held rigidly within some form of matrix or body until the high explosive (HE) filling is detonated. The resulting high velocity fragments produced by either method are the main lethal mechanisms of these weapons, rather than the heat or overpressure caused by detonation.

The modern fragmentation grenade was developed during the 20th century. The Mills bomb, first adopted in 1915 by the British army, is an early fragmentation grenade used during the First World War. The Mk2 grenade was a fragmentation grenade adopted by the American military based on the Mills bomb, and was in use during the Second World War.

Difference between fragmentation and shrapnel
The term shrapnel is often incorrectly used to refer to fragments produced by any explosive weapon. However, the Shrapnel shell (named from Major General Henry Shrapnel of the British Royal Artillery) predates the modern high-explosive shell and operates via an entirely different process.

A shrapnel shell consists of a shell casing filled with steel or lead balls suspended in a resin matrix, with a small explosive charge at the base of the shell. When the projectile is fired, it travels a pre-set distance along a ballistic trajectory before the fuse ignites a relatively weak secondary charge (often black powder or cordite) in the base of the shell. This charge fractures the matrix holding the balls in place and expels the nose of the shell to open a path for the balls, which are then propelled out of the front of the shell without rupturing the casing (which falls to earth harmlessly and can be retrieved and reused). These balls continue onward to the target, spreading out in a cone-shaped pattern to strike the earth, with most of their energy coming from the original velocity of the shell itself, rather than the lesser force of the secondary charge that freed them from the shell. Since the cone of impact is relatively small, shrapnel shells needed to be carefully sighted and judiciously used in order to maximize their impact on the enemy.

In contrast, a high-explosive shell contains a relatively large and energetic secondary charge of high explosive (known as a burster charge) which, when ignited by the fuse, produces a powerful supersonic shock wave that shatters the entire shell casing into many fragments that fly in all directions. The use of high explosives with a fragmenting case improves efficiency as well as propelling a larger number of fragments at a higher velocity over a much wider area (40-60 times the diameter of the shell), giving high-explosive shells a vastly superior battlefield lethality that was largely impossible before the Industrial Era. The First World War was the first major conflict in which HE shells were the dominant form of artillery; the failure to adapt infantry tactics to the massive increase in lethality they produced was a major element in producing the ghastly subterranean stalemate conditions of trench warfare, in which neither side could risk movement above ground without the guarantee of instant casualties from the constant, indiscriminate hail of HE shell fragments.