It is believed that the use of the .50 Caliber Machine Gun on human targets is banned under the Geneva Convention. This, however, is a myth as the US has insisted that all their weapons are reviewed before entering into service.
The M2 has been used by the United States in almost all its conflicts since its production. The long list includes WW2, Korean War, Suez Crisis, Vietnam War, Iraq War, Invasion of Panama, Somali War, War in Afghanistan, etc.
As an anti-aircraft weapon on ships, even 6x M2 guns can be mounted on the same turret. While on the ground, the M2 is used in either twin or quadruple mode.
The AN/M2 and AN/M3 variants have been put to use on US pursuit aircraft like the P-51 Mustang, P-38 Lighting, P-40 Tomahawk, etc. during WW2 and F-80 Shooting Star, Thunderjet and Sabre in the Korean War. Other aircraft variants include XM213, GAU-15/A, GAU-21A, and M3P.
The M2 is even used as a sniper rifle when equipped with a telescopic sight. This was a common technique during the Korean & Vietnam War when such an aggressive weapon was combined with a sniper scope. The US Marine Corps sniper Carlos Hathcok is credited for practical use of this technique as he used his M2 to take down targets over 1800 meters, twice the range of an average sniper rifle of the time!
When the IRA used the .50 Caliber Machine Gun in Northern Island to shoot at soldiers & police officers, the media gave the weapon worldwide notoriety as a gun for Snipers.
The Unit Replacement Cost of the standard M2 Machine gun is around $14,000.
The M2 Machine Gun is used by almost all countries, not under an arms embargo by the US. M2HB is the most sold variant of the .50 Caliber Machine Gun.
During the design phase and initial prototype development, the power of the gun was so paramount that it was restricted to experimental use only right until 1937. Surely, the M2 Browning is one of the best machine guns ever.