The Lewis gun is a First World War–era light machine gun. Designed privately in the United States though not adopted there, the design was finalised and mass-produced in the United Kingdom, and widely used by troops of the British Empire during the war. It had a distinctive barrel cooling shroud, and top-mounted pan magazine. The Lewis served until the end of the Korean War, and was widely used as an aircraft machine gun during both World Wars, almost always with the cooling shroud removed, as air flow during flight provided sufficient cooling.