During World War I, the British adopted the US-designed Lewis gun as an infantry weapon, realizing that its light weight and the fact that it could be fired both prone and on the move made it ideal for supporting advances and defending captured trenches. It was reliable and surprisingly enduring design and was copied by the Japanese Imperial Army and used in WW2. Weighing in at 28 lb (12.7 kg), it was only half the weight of Vickers and other machine gun of the time. This was particularly important when used on the aircraft in the WW1 era.
In the Fall of France, a large part of the British Army's equipment was lost and mothballed stocks of Lewis guns in both .303 and .30-06 were re-introduced into service by the British. In addition to their reserve weapon role in the UK, they also saw front-line use with Commonwealth forces in the early years of the Pacific campaign against the Japanese. The Lewis gun also used as an anti-aircraft weapon during World War II; in this role it was credited by the British for bringing down more low-flying enemy aircraft than any other AA weapon.