The men who served in the British Army during the war were almost exactly split between volunteers and conscripts. Just under five million men served in the Army with another half million or so in the Royal Navy and Royal Air Force. Recruits were required to be between the ages of 19 and 35, to be at least 5 feet 6 inches tall and to have a chest measurement of 34 inches. The height was quickly reduced to 5ft 3in in October 1914, when the numbers volunteering began to drop.
All in all about 2.5m men volunteered for military service up until the end of 1915, of whom nearly a third joined in the first eight weeks of the war. Numbers soon fell away, and the authorities had to resort to increasingly desperate measures to keep the numbers up.
Conscription commenced in March 1916. Initially only unmarried men were called to the colours, however in May 1916 the scheme was extended to married men between the ages of 18 and 41. For political reasons Ireland was excluded. Men working in key trades, such as miners and steelworkers, were exempt from conscription.
Some 702,410 British servicemen lost their lives (37,452 offices and 664.958 other ranks). Proportionally, however, casualties were much higher among junior officers (Second Lieutenants and Lieutenants) who led their platoons and sections on raids and over the top into battle. In addition just under a million men were wounded in some way.