The Browning M2 is a .50 caliber (12.7 mm) machine gun and entered service towards the end of World War I. It is a heavy-duty machine gun designed by John Browning and was first introduced as the M1921. In 1932, the design was updated and redesignated as the M2, but was often referred to as the "fifty-cal". Although rather large for a machine gun, it was light enough for aircraft use, it became the standard USA gun for aircraft armament. The P-47 Thunderbolt carried eight M2s in the wings and in USAAF bombers it was configured with fixed or flexible mounts and in twin, and quadbarrel turrets.

    With its high rate of fire from 500 to 650 rounds per minute, it was used heavily during World War II, the Korean War and the Vietnam War and is still in use today, with only a few modern improvements. It was also used in both Iraq wars during Desert Storm and Operation Enduring Freedom. Presently, it is the primary heavy machine gun of NATO countries, and is used by other countries as well. The M2 has been in service longer than any other small arm in US inventory and was very similar in design to the smaller Browning 1919 .30 caliber machine gun.

    It was sometimes referred to as the "Ma Deuce" for its M2 designation.