This is the story of how the nearly five million British men enlisted into the British Army during the First World War were transformed from civilians into infantry soldiers, and how this process shaped each man's identity, his experience of the war, and his performance on the battlefield. Stephen Graham, recording his experiences in the First World War, summed up this transformation by describing training as 'the soldiery factory in which you go in at one end civilian and pass out eventually at the other side a soldier of the king'. The Soldier Factory is the first work to examine how the training process worked within the British Army in-depth. It focuses on how training created infantrymen, as while aeroplanes, artillery, chemical weapons, machine guns, and tanks turning the battlefield into an industrialised killing zone, it was still the infantryman who led the advance into battle and conquered enemy positions. And the infantry bore the consequences: of 1,677,163 British casualties on the Western Front, 1,372,117 were infantrymen. The Soldier Factory reveals that training was an inconsistent process, with nuances, evolutions, improvements, and regressions in its effectiveness which altered the type of infantryman it produced, the very nature of what a British infantryman was, and his effectiveness on the battlefield at different points in the war. The infantryman who arrived at the front in 1914 was almost unrecognisable from that of 1916, who was almost unrecognisable from that of 1918.