The M1919 Browning is a .30 caliber medium machine gun that was widely used during the 20th century. It was used as a light infantry, coaxial, mounted, aircraft, and anti-aircraft machine gun by the U.S. and many other countries, especially during World War II, the Korean War, and the Vietnam War. Although it began to be superseded by newer designs in the later half of the century (such as by the M60 machine gun), it remained in use in many North Atlantic Treaty Organization (NATO) countries and elsewhere for much longer. It is very similar in design to the larger .50 in (12.7 mm) M2 Machine Gun, which is also a Browning-designed weapon and is still in NATO service.
Many M1919s were rechambered for the new 7.62 × 51 mm NATO round and served into the 1990s, as well as up to the present day in some countries. The United States Navy also converted many to 7.62 mm NATO, and designated them Mk 21 Mod 0; they were commonly used on river craft in the 1960s and 1970s in Vietnam.