The M1917 Browning machine gun is a heavy machine gun used by the United States armed forces in World War I, World War II, the Korean War, and the Vietnam War; it has also been used by other nations. It was a crew-served, belt-fed, water-cooled machine gun that served alongside the much lighter air-cooled Browning M1919. It was used at the battalion level, and often mounted on vehicles (such as a jeep). There were two main iterations: the M1917, which was used in World War I and the M1917A1, which was used thereafter. The M1917, which was used on some aircraft as well as in a ground role, had a cyclic rate of 450 rounds per minute. The M1917A1 had a cyclic rate of 450 to 600 rounds per minute.