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 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 infantry type is Browning Machine Gun, Cal. .50, M2, HB, Flexible. It has been used against infantry, light armored vehicles, watercraft, 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 Gulf War, the War in Afghanistan, and the Iraq War. 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 M2HB (heavy barrel) is manufactured in the U.S. by General Dynamics, Ohio Ordnance Works, U.S. Ordnance, and FN Herstal for sale to the U.S. government and other nations via Foreign Military Sales.
History Machine guns were heavily used in World War I, and weapons of larger-than-rifle caliber began appearing on both sides of the conflict. The larger rounds were needed to pierce the armor that was being introduced to the battlefield, both on the ground and in the air. Germany introduced the Junkers J.I aircraft, whose armor could render ineffective aircraft machine guns that used conventional rifle ammunition such as the .30-06., stating "The Germans put a heavily armored plane into service during the closing days of World War I. This act made obsolete for all time the rifle-caliber machine gun for aerial use. Some countries were slower to accept the fact than others but nevertheless, it cannot be disputed. The United States was among the first to come to this realization." Consequently, the American Expeditionary Force's commander General John J. Pershing asked for a larger-caliber machine gun. Pershing asked the Army Ordnance Department to develop a machine gun with a caliber of at least and a muzzle velocity of at least .
Around July 1917, John Browning began redesigning his .30-06 M1917 machine gun to use a larger and more powerful round. Winchester worked on the cartridge, which was a scaled-up version of the .30-06. Winchester initially added a rim to the cartridge because the company intended to use the cartridge in an anti-tank rifle, but Pershing insisted the cartridge be rimless. The first .50-caliber machine gun underwent trials on 15 October 1918. It fired at less than 500 rounds per minute, and the muzzle velocity was only . Cartridge improvements were promised. The gun was heavy, difficult to control, fired too slowly for the anti-personnel role, and lacked sufficient power for the anti-armor role.
While the .50-caliber was being developed, some 13.2×92mmSR Mauser 1918 T-Gewehr anti-tank rifles and their ammunition were captured. The 13.2 mm German rounds had a muzzle velocity of , an bullet, and could penetrate armor thick at a range of .. Chinn states that the German round was 12.7-mm anti-tank, but it may have been the 13.2mm TuF round. The Germans were working on their MG 18 TuF heavy machine gun. Winchester improved the .50 caliber round to have similar performance. Ultimately, the muzzle velocity was .
Efforts by Browning and Fred T. Moore resulted in the water-cooled, .50-caliber M1921 Browning machine gun and an aircraft version. These guns were used experimentally from 1921 until 1937. They had lightweight barrels and the ammunition fed only from the left side. Service trials raised doubts about whether the guns would be suitable for aircraft or for anti-aircraft use. A heavy-barrel M1921 was considered for ground vehicles.
John M. Browning died in 1926. Between 1927 and 1932, S. H. Green studied the design problems of the M1921 and the needs of the armed services. 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 new receiver allowed right or left side feed. In 1933, Colt manufactured several prototype Browning machine guns (including what would be known as the M1921A1 and M1921E2). With support from the Navy, Colt started manufacturing the M2 in 1933. FN Herstal () has manufactured the M2 machine gun since the 1930s. General Dynamics, U.S. Ordnance and Ohio Ordnance Works Inc. are other current manufacturers.
A variant without a water jacket, but with a thicker-walled, air-cooled barrel was designated the M2 HB (HB for Heavy Barrel). The added mass and surface area of the heavy barrel compensated somewhat for the loss of water-cooling, while reducing bulk and weight: the M2 weighs with a water jacket, but the M2 HB weighs . Due to the long procedure for changing the barrel, an improved system was developed by FN Herstal called QCB (quick change barrel). The lightweight "Army/Navy" prefixed AN/M2 "light-barrel" version of the Browning M2 weighing 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, readily replacing Browning's own air-cooled .30 caliber machine gun design in nearly all American aircraft installations.
Design details
The Browning M2 is an air-cooled, belt-fed machine gun, essentially a scaled-up version of John Browning's M1917 .30 caliber machine gun. The M2 fires from a closed bolt, operated on the short recoil principle. The M2 fires the .50 BMG cartridge, which offers long range, high accuracy, and immense stopping power. 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.
Features The M2 has varying cyclic rates of fire, depending on the model. The M2HB air-cooled ground gun has a cyclical rate of 450–575 rounds per minute.: "The official rate during WWII was 450–575 rpm, but it was extremely rare to encounter an M2HB that exceeded 550 rpm." The early M2 water-cooled AA guns had a cyclical rate of around 450–600 rpm. The AN/M2 aircraft gun has a cyclic rate of 750–850 rpm; this increases to 1,200 rpm for AN/M3 aircraft guns. These maximum rates of fire are generally not achieved in use, as sustained fire at that rate will wear out the bore within a few thousand rounds, necessitating replacement. In addition to full automatic, the M2HB can be selected to fire single shots, fire slowly at less than 40 rounds per minute, or fire rapidly for more than 40 rounds per minute. Slow and rapid firing modes use 5–7 round bursts with different lengths of pause between bursts.
The M2 has an effective range of and a maximum effective range of when fired from the M3 tripod. In its ground-portable, crew-served role as the M2HB, the gun itself weighs and the assembled M3 tripod another . 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. The spade handles are gripped and the butterfly trigger is depressed with one or both thumbs. Recently, new rear buffer assemblies have used squeeze triggers mounted to the handgrips, doing away with the butterfly triggers.
When the bolt release is locked down by the bolt latch release lock on the buffer tube sleeve, the gun functions in fully automatic mode. Conversely, the bolt release can be unlocked into the up position resulting in single-shot firing (the gunner must press the bolt latch release to send the bolt forward). Unlike virtually all other modern machine guns, it has no safety (although a sliding safety switch has recently been fielded to USMC armorers for installation on their weapons and is standard issue for the U.S. Army for all M2s). 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. The upgraded M2A1 has a manual trigger block safety.
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. The operator must also convert the top-cover belt feed slide assembly from left- to right-hand feed as well as the spring and plunger in the feed arm. A skilled operator can perform this conversion in under two minutes.
The charging assembly can also be swapped from left-hand to right-hand charge, though a right-hand charging handle spring is required. The M2 can be more easily interchanged if it is preemptively fitted with a retracting slide assembly on both sides of the weapon system.
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.
Ammunition There are several different types of ammunition used in the M2HB and AN aircraft guns. From World War II through the Vietnam War, the Browning was used with standard ball, armor-piercing (AP), armor-piercing incendiary (API), and armor-piercing incendiary tracer (APIT) rounds. All .50 ammunition designated "armor-piercing" was required to completely perforate of hardened steel armor plate at a distance of and at . 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.
Current ammunition types include M33 Ball (706.7 grain) for personnel and light material targets, M17 tracer, M8 API (622.5 grain), M20 API-T (619 grain), and M962 SLAP-T. The latter ammunition along with the M903 SLAP (Saboted Light Armor Penetrator) round can perforate of FHA (face-hardened steel plate) at , at , and at . This is achieved by using a tungsten penetrator. The SLAP-T adds a tracer charge to the base of the ammunition. This ammunition was type classified in 1993.
When firing blanks, a large blank-firing adapter (BFA) of a special type must be used to allow the recoil-operated action to cycle. This functions on the principle of a recoil booster, to increase the recoil force acting on the short recoil action. This is the exact antithesis of a muzzle brake. Without this adaptor, the reduced-charge blank cartridge would develop too little recoil to cycle the action fully. The adapter is very distinctive, attaching to the muzzle with three rods extending back to the base. The BFA can often be seen on M2s during peacetime operations.
Deployment
The M2 .50 Browning machine gun has been used for various roles: A medium infantry support weapon As a light anti-aircraft (AA) gun in some ships; up to six M2 guns could be mounted on the same turret. As an anti-aircraft gun on the ground. The original water-cooled version of the M2 was used on a tall AA tripod or vehicle-mounted anti-aircraft weapon on pedestal mount. In later variants, twin and quadruple M2HB Brownings were used, such as the M45 Quadmount (aka "meat chopper") used on the U.S. M16 half-track carrier. Twin or quad-mount .50 M2 guns normally used alternating left-hand and right-hand feed. Primary or secondary weapon on an armored fighting vehicle. Primary or secondary weapon on a naval patrol boat. Spotting for the primary weapon on some armored fighting vehicles. Secondary weapon for anti-boat defense on large naval vessels (corvettes, frigates, destroyers, cruisers, etc.).