The M2 machine gun or Browning .50 caliber machine gun (informally, "Ma Deuce" is a heavy machine gun that was designed near the end of World War I by John Browning. While similar to Browning's earlier M1919 Browning machine gun, which was chambered for the .30-06 cartridge, the M2 uses Browning's larger and more powerful .50 BMG (12.7 mm) cartridge. The design has had many designations; the official U.S. military designation for the current infantry type is Browning Machine Gun, Cal. .50, M2, HB, Flexible. It is effective against infantry, unarmored or lightly armored vehicles and boats, light fortifications, and low-flying aircraft.

The gun has been used extensively as a vehicle weapon and for aircraft armament by the United States since the 1930s. It was heavily used during World War II, the Korean War, the Vietnam War, the Falklands War, the Soviet–Afghan War, the Gulf War, the Iraq War, and the War in Afghanistan. It is the primary heavy machine gun of NATO countries and has been used by many other countries as well. U.S. forces have used the M2 longer than any other firearm except the .45 ACP M1911 pistol, which was also designed by John Browning.

The current M2HB (heavy barrel) is manufactured in the U.S. by General Dynamics[12] Ohio Ordnance Works,[13] and U.S. Ordnance[14] for sale to the U.S. government and to allies via Foreign Military Sales. Foreign manufacturers such as FN Herstal produce it under licence.