US medium machine gun. A water-cooled, tripod-mounted, belt-fed gun of 30 in caliber, it was adopted by the US Army 1917 and is still in use in most countries. Resembling the Vickers and Maxim guns, the original design was operated by recoil force and fired at about 500 rounds per minute.
The original design was modified to an air-cooled version after World War I and extensively used as an aircraft and tank machine gun. A 50 in caliber version was also developed as an antiaircraft weapon 1919 and later saw extensive use as an infantry support and tank weapon.