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. Design and development In 1900, John Moses Browning filed a patent for a recoil-powered automatic gun. Browning did not work on the gun again until 1910, when he built a water-cooled prototype of the 1900 design. Although the gun worked well, Browning improved the design slightly. Browning replaced side ejection with bottom ejection, added a buffer for smoother operation, replaced the hammer with a two piece firing pin, and some other minor improvements. The basic design of the gun was still the 1900 design. The Browning is a water-cooled heavy machine gun, though some experimental versions were made that did not use a water jacket; the air-cooled M1919 was later developed as a medium machine gun. Unlike many other early machine guns, the M1917 had nothing to do with Maxim's toggle lock design. At , it was much lighter than contemporary Maxim type guns such as the first German Maschinengewehr 08 (08/15 model: ) and the British Vickers machine gun, while still being highly reliable. The only similarities with the Maxim or Vickers are the principles of recoil operation, T-slot breechblock, "pull-out" belt feed, water cooling, and forward ejection. Its sliding-block locking mechanism saved weight and complexity, and was used in many previous Browning designs. The belt fed left-to-right, and the cartridges were stacked closer together than Maxim/Vickers (patterns copied by most guns later). The Army Ordnance Department showed little interest in machine guns until war was declared in April 1917. At that time, the U.S. arsenal included only 1,100 machine guns, and most of those were outmoded. The government asked several designers to submit weapons. Browning arranged a test