[19] Pershing asked the Army Ordnance Department to develop a machine gun with a caliber of at least 0.50 inches (12.7 mm) and a muzzle velocity of at least 2,700 feet per second (820 m/s).

The result was a single receiver design that could be turned into seven types of .50 caliber machine guns by using different jackets, barrels, and other components.

The lightweight "Army/Navy" prefixed AN/M2 "light-barrel" version of the Browning M2 weighing 60 pounds (27 kg) was also developed, and became the standard .50-caliber aviation machine gun of the World War II–era for American military aircraft of nearly every type,[28][better source needed] readily replacing Browning's own air-cooled .30 caliber machine gun design in nearly all American aircraft installations.

The closed bolt firing cycle made the M2 usable as a synchronized machine gun on aircraft before and during World War II, as on the early versions of the Curtiss P-40 fighter.

In this configuration, the V-shaped "butterfly" trigger is located at the very rear of the weapon with a "spade handle" handgrip on either side of it and the bolt release in the center.

Troops in the field have been known to add an improvised safety measure against accidental firing by slipping an expended shell casing under the butterfly trigger.

Because the M2 was designed to operate in many configurations, it can be adapted to feed from the left or right side of the weapon by exchanging the belt-holding pawls, and the front and rear cartridge stops (three-piece set to include link stripper), then reversing the bolt switch.

At some point during World War II, the Frankford Arsenal developed a squeeze bore version of the M2HB which reduced the bullet size from .50 to .30 caliber.

[34] The API and APIT rounds left a flash, report, and smoke on contact, useful in detecting strikes on enemy targets; they were primarily intended to incapacitate thin-skinned and lightly armored vehicles and aircraft, while igniting their fuel tanks.

[citation needed] When firing blanks, a large blank-firing adapter (BFA) of a special type must be used to allow the recoil-operated action to cycle.

In the dual-purpose vehicle mount, the M2HB proved extremely effective in U.S. service: the Browning's .50 caliber AP and API rounds could easily penetrate the engine block or fuel tanks of a German Bf 109 fighter attacking at low altitude,[39] or perforate the hull plates and fuel tanks of a German half-track or light armored car.

[43] The weapon was particularly hated by the Germans, whose attacks and ambushes against otherwise helpless stalled motor convoys were frequently broken up by .50 caliber machine gun fire.

[46] Mounted on a heavily sandbagged tripod, the M2HB proved very useful in either a defensive role or to interdict or block road intersections from use by German infantry and motorized forces.

[50][51][52] The M2HB was not widely used in the Pacific campaign for several reasons, including the weight of the gun, the nature of infantry jungle combat, and because road intersections were usually easily outflanked.

[56] Towards the end of the war, as Luftwaffe attacks became less frequent, the quad .50 (nicknamed the Meat Chopper or Krautmower[56]) was increasingly used in an anti-personnel role, similarly to the earlier-introduced (1940) and more powerful—but much more difficult to keep well-fed with ammunition when in action—German 20 mm Flakvierling.

The Commonwealth use of the M2 Browning .50 caliber machine gun (known as the .5 Browning in British and Commonwealth service) began in World War II, though from 1942 it was standard armament on US-built AFVs provided under lend-lease such as the M4 Sherman, M7 Priest, M8 Greyhound, or M10 tank destroyer variously used by British, Canadian, Australian, South African, and New Zealand units.

Nigerian troops have extensively deployed the 50 caliber Browning, mounted on Otokar Cobra APCs, Panhard VBL M11s and Landcruiser gun-trucks in counterinsurgency operations in the Niger Delta, N.E Nigeria, the Jos Plateau, and in Mali.

In response to incidents involving North Korean suspicious ships, the M2 machine guns were reintroduced on some vessels as more appropriate firepower for engaging small targets.

[65] In April 2021, Sumitomo Heavy Industries announced it would cease production of machine guns, although it intends to continue manufacturing parts for maintenance and repairs.

Using an Unertl telescopic sight and a mounting bracket of his own design, Hathcock could quickly convert the M2 into a sniper rifle, using the traversing-and-elevating (T&E) mechanism attached to the tripod.

When firing semi-automatically, Hathcock hit man-size targets beyond 1,800 metres (2,000 yd)—twice the range of the standard-caliber sniper rifle of the time (a .30-06 Winchester Model 70).

The 12.7 mm AN/M2 had a cyclic rate of 600–800 rounds per minute, with the ability to be fired from an electrically operated remote-mount solenoid trigger when installed as a fixed gun.

[87] Cooled by the aircraft's slip-stream, the air-cooled 12.7 mm AN/M2 was fitted with a substantially lighter 36-inch (91 cm) length barrel, reducing the weight of the complete unit to 61 pounds (28 kg),[87][88] which also had the effect of increasing the rate of fire.

Two are installed in the Embraer EMB 314 Super Tucano aircraft as a fixed wing-mounted standard weapon as designated as M3W with minor modification with reduced weight barrel, electronic box triggered from the cockpit with 250 rounds each.

[citation needed] The Air Force is looking to replace the GAU-18 on the HH-60G Pave Hawk with the GAU-21 because of its higher 1,100 rpm rate of fire, longer 10,000-round barrel life, and lower recoil through the use of a soft mount.

[93] The M3M is also the primary machine gun used by the British Royal Navy's Fleet Air Arm for helicopter armament on Wildcat and Merlin aircraft.

The Saint Petersburg Declaration of 1868 states that the "military or naval" use of explosive or incendiary projectiles with a mass of under 400 g (14 oz) is forbidden by its signatory parties.

[137] The origin of these myths is likely due to military commanders instructing their troops to conserve ammunition for targets that other lighter machine guns were not well suited to engage, such as aircraft or ground vehicles.

One possible source of the misconception is from World War II, when American half-track units in Germany were told to stop firing their M2s at ground targets, to conserve ammunition in case of a Luftwaffe attack.

[139] It is also possible that a restriction during the latter period limiting the use of the M40 recoilless rifle's .50-caliber spotting gun to destroy enemy equipment only, since the M40 was meant to be used against armor and firing it at personnel would give away their position before it could be used as intended, was mistakenly applied to all .50 caliber weapons.