The M1917 Browning machine gun is a heavy machine gun used by the United States armed forces in World War I, World War II, Korea, and to a limited extent in Vietnam; it has also been used by other nations. It was used at the battalion level, and often mounted on vehicles. There were two main iterations of it: 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. 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 47 pounds, it was much lighter than contemporary Maxim type guns such as the first 137-pound 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 principle 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. 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 at the Springfield Armory in May 1917. In the first test, the weapon fired 20,000 rounds without incident. The reliability was exceptional, so Browning fired another 20,000 rounds through the weapon without any parts failing. The Ordnance Board was impressed, but was unconvinced that the same level of performance could be achieved in a production model. Consequently, Browning used a second gun that not only duplicated the original trial, but it also fired continuously for 48 minutes and 12 seconds. The Army adopted the weapon as its principal heavy machine gun, utilizing the M1906 .30-06 cartridge with a 150-grain, flat-base bullet. Unfortunately, production was a problem. Several manufacturers started producing the gun, but they had to set up the assembly lines and tooling. By June 30, 1918, Westinghouse had made only 2,500 and Remington had made only 1,600. By the time of the Armistice, Westinghouse had made 30,150, Remington 12,000, and Colt 600.
Until the start of World War I, the Army had used a variety of older machine guns, like the M1895 Colt–Browning machine gun "Potato Digger" and weapons like the Maxim Gun, the Benet–Mercie M1909, and the Hotchkiss M1914 machine gun. Although the Model 1917 was intended to be the principal US Army heavy machine gun in the war, the Army was, in fact, forced to purchase many foreign weapons—the French-produced Hotchkiss 8 mm machine gun was actually the most numerous heavy machine gun used by the American Expeditionary Force. In 1926, the Browning's rear sight was revised to incorporate scales for both the new M1 Ball (172-grain boat-tail bullet) and the M1906 (150-grain flat-base bullet) ammunition. With M1 ball, the M1917 had a maximum range of about 5,500 yd; with M2 ammunition, about 3,500 yd (3,200 m). The rear sight had a battle sight as well as a raised leaf-type sight suitable for employment against either ground or air targets.
The M1917 saw limited service in the later days of World War I. Because of production delays, only about 1,200 Model 1917s saw combat in the conflict, and then only in the last 2½ months of the war. Some arrived too late for combat service. The Model 1917A1 was again used in the Second World War, and was primarily used with the M2 ball, tracer, and armor-piercing ammunition introduced just prior to the outbreak of hostilities.
The Model 1917 was called to service again in the Korean War. On at least one occasion, U.S. soldiers in the Korean War urinated on the gun when water-cooling had failed in the frigid temperatures of the Korean winter. The Model 1917 was slowly phased out of military service in the late 1960s in favor of the much lighter M60 machine gun chambered in the new 7.62mm NATO cartridge.