The Lewis gun (or Lewis automatic machine gun or Lewis automatic rifle) is a First World War-era light machine gun of US design that was perfected and mass-produced in the United Kingdom, and widely used by British and British Empire troops during the war. With its distinctive barrel cooling shroud and top-mounted pan magazine, the Lewis served to the end of the Korean War. It was also widely used as an aircraft machine gun, almost always with the cooling shroud removed, during both world wars.