The Lewis gun (or Lewis automatic machine gun or Lewis automatic rifle) 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 (containing a finned, aluminium breech-to-muzzle heat sink to cool the gun barrel) and top-mounted pan magazine. The Lewis served to 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 offers sufficient cooling.