The vast corpse factory of the Western Front took a lot of raw material to feed, and it soon became obvious to most of the participants in the Great War that prewar standards for cannon fodder would need to be relaxed if their General Staffs' demands for fresh casualties were going to be met.
The British, who alone among the major combatants had entered the war with a non-conscript professional army, came up with several schemes to raise the numbers of troops required to be taken seriously in this life-sized game of RISK.
One of these was the "Pals battalion", where groups of volunteers from a single company or school or sports club or neighborhood were encouraged to enlist together, with the promise that they would all be kept together through training and combat, rather than allotted out piecemeal to replacement units. This allowed small British communities to share the experience of having huge actuarial holes blown in their census tables with their continental allies, who used the more usual system of regional conscription.
Further, it quickly became apparent that the British army's minimum height requirement of 5'3" was perhaps a bit strict, as someone who was 5'1" could get blown apart by a torrent of Maxim bullets as well as any six-footer, and the dark Satanic mills and mines of post-Edwardian Britain were well-stocked with burly kobolds who could lug a pack like nobody's business. "Bantam battalions" were quickly organized, where the height requirement was reduced to 5'nowt" in order to give shorter guys the chance to get their own taste of dulce et decorum.
When the Lancashire Fusiliers moved into the line before the Somme offensive, their numbers included three Pals battalions as well as three Bantam battalions. One wonders if a young signals leftenant of the Fusiliers, one 2Lt. John Tolkien, witnessed the stubborn courage of the latter and got any ideas for future writings.