The M1921 Browning machine gun was a water-cooled .50-caliber machine gun, designed by John Moses Browning, which entered production in 1929.
Developed from the prototype .50-caliber M1918, itself developed from .30-caliber M1917 water-cooled machine gun. A slightly improved version, the M1921A1, was introduced in 1930 with all of the M1921s being upgraded. The gun weighed 79 pounds (without water), was 56 inches long, and had a 36-inch long barrel. The gun was mounted on a pedestal mount with three horizontal legs. It had a 500-650 rounds per minute rate of fire.
Development continued and the M1921A1 was replaced by the M2 air-cooled Browning .50-caliber in 1933. Ground and aircraft air-cooled versions of the M2 were also adopted at the same time.
Both the US Army and the US Navy adopted the M1921 after World War I, using it mostly as a static anti-aircraft weapon due to its 121 lb weight.