Submachine Gun, Cal. .45, M3
World War II-era Guide Lamp M3 submachine gun with 30-round magazine and other accessories. The Buffalo Arms bolt in this original M3 is dated January 1944.
Type	Submachine gun
Place of origin	United States
Service history
In service	1943–1992 (US) Philippines (revived 2004)
Wars	World War II[1] Chinese Civil War Greek Civil War[2] Korean War[1] Bay of Pigs Invasion Vietnam War[1] The Troubles Argentine Dirty War Falklands War[3] Persian Gulf War[4]
Production history
Designer	George Hyde
Designed	1942
Manufacturer	General Motors, others
Unit cost	Approx. USD $15 (1943; equivalent to $208 in 2016)[5]
Produced	1943–1945
No. built	622,163; 606,694 M3 15,469 M3A1
Variants	M3A1 PAM1 PAM2
Specifications
Weight	M3 (empty): 8.15 lb (3.70 kg) M3A1 (empty): 7.95 lb (3.61 kg)
Length	29.8 in (760 mm) stock extended / 22.8 in (579.1 mm) stock collapsed
Barrel length	8 in (203.2 mm)
Cartridge	.45 ACP (11.43×23 mm) 9×19mm Parabellum
Action	Blowback, open bolt
Rate of fire	450 rounds/min cyclic
Muzzle velocity	920 ft/s (280 m/s)
Effective firing range	Sights fixed to 100 yards (91 m)[6]
Feed system	30-round detachable box magazine
Sights	Fixed rear peep sight and blade foresight, calibrated to 100 yards for caliber .45 M1911 ball ammunition[6]

The M3 was an American .45-caliber submachine gun adopted for U.S. Army service on 12 December 1942, as the United States Submachine Gun, Cal. .45, M3.^[6] The M3 was chambered for the same .45 round fired by the Thompson submachine gun, but was cheaper to produce, and lighter, although, contrary to popular belief, it was far less accurate.^[6] This myth stems from a US army training film portraying the M3 as more accurate than its counterparts.^[7] The M3 was commonly referred to as the “Grease Gun” or simply “the Greaser,” owing to its visual similarity to the mechanic’s tool.^[8]
Intended as a replacement for the .45-caliber Thompson series of submachine guns, the M3 began to replace the Thompson in first-line service in mid-1944. Due to delays caused by production issues and approved specification changes, the M3 saw limited combat use in World War II and the M3A1 none.^[6] The M3A1 was used in the Korean War and later conflicts.

History[edit]

M3 in use in Brittany, France, August 1944

In 1941, the U.S. Army Ordnance Board observed the effectiveness of submachine guns employed in Western Europe, particularly the German 9×19mm MP 40 and British Sten guns, and initiated a study to develop its own Sten-type submachine gun in October 1942.^[8]The Ordnance Department requested the army submit a list of requirements for the new weapon, and ordnance in turn received a separate list of requirements from both the infantry and cavalry branches for a shoulder-fired weapon with full- or semi-automatic fire capability in caliber .45 ACP or .30 Carbine.^[6]
The two lists of requirements received by ordnance were then reviewed and amended by officials at Aberdeen Proving Ground. The amended requirement called for an all-metal weapon of sheet metal construction^[9] in .45 ACP caliber, designed for fast and inexpensive production with a minimum of machining, and featuring a dual full-automatic and semi-automatic fire capability, a heavy bolt to keep the cyclic rate under 500rpm, and the ability to place 90 percent of all shots fired from a standing position in full-automatic mode on a 6×6 foot target at a range of 50 yards.^[6] The benchmark for testing the M3’s performance would be the M1928A1 Thompson.^[6]
George Hyde of General Motors‘s Inland Division was given the task of designing the new weapon, while Frederick Sampson, Inland Division’s chief engineer, was responsible for preparing and organizing tooling for production. The original T15 specifications of 8 October 1942 were altered to remove a semi-automatic fire function, as well as to permit installation of a kit to convert the weapon’s original .45 caliber to that of 9mm Parabellum.^[6] The new designation for the 9mm/.45 full-automatic-only weapon was the T20.^[6]
Five prototype models of the .45 T20 and five 9mm conversion kits were built by General Motors for testing. At the initial military trials, the T20 successfully completed its accuracy trials with a score of 97 out of 100.^[6] In the endurance test, the test weapon fired more than 5,000 rounds of brass-case ammunition, with only two failures to feed.^[6] Four army test boards composed of multiple army service branches independently tested and reviewed the T-20 prototype weapons including the Airborne Command, the Amphibious Warfare Board, the Infantry Board, and the Armored Forces Board.^[6] All four branches reported malfunctions caused by the M3 magazine, mostly attributed to defective or jammed magazine followers.^[6]
The T20 was formally approved by U.S. Army Ordnance for production at GM’s Guide Lamp Division in Anderson, Indiana in December 1942 as the U.S. Submachine Gun, Caliber .45, M3.^[6] Guide Lamp produced 606,694 of the M3 variant submachine gun between 1943 and 1945.^[6] Although reports of malfunctions caused by the single-feed magazine design appeared during the initial firing trials, no changes were made to the M3 magazine.^[6]
Around one thousand M3 submachine guns in caliber 9mm Parabellum were built by Guide Lamp.^[10] These original 9mm guns, identified by the markings “U.S. 9 mm S.M.G.” on the left side of the magazine well (without any model designation, such as M3), were delivered to the OSS in 1944. Additionally, Rock Island Arsenal and Buffalo Arms Corporation manufactured parts for a limited number of 9mm conversion kits for the M3.^[11] Though 25,000 kits were originally requested for procurement, this was changed to a recommendation by the Ordnance Committee in December 1943 that only 500 9mm conversion kits be obtained.^[11] Procurement was authorized in February 1944, but it is believed that only a limited number of kits were actually produced.^[11] These conversion kits included a new 9mm barrel, replacement bolt and recoil springs, a magazine well adapter for use with British Sten gun 32-round magazines, and a replacement 9mm Sten magazine of British manufacture.^[11] As the M3’s sights were not altered for the new cartridge, the 9mm M3 shot high at 100 yards, but the sighting error was deemed inconsequential. The OSS also requested approximately 1,000 .45-caliber M3 submachine guns with an integral sound suppressor (designed by Bell Laboratories). Specially drilled barrels and barrel nuts were manufactured by Guide Lamp, while the High Standard Firearms Company produced the internal components and assembled the weapon.^[12] The Bell Laboratories suppressor was estimated to be only 80% as efficient as the British suppressed STEN Mk IIS.^[13]
With its stamped, riveted, and welded construction, the M3 was originally designed as a minimum-cost small arm, to be used and discarded once it became inoperative.^[14][15] As such, replacement parts, weapon-specific tools, and sub-assemblies were not made available to unit-, depot-, or ordnance-level commands at the time of the M3’s introduction to service.^[16][17] In 1944, a shortage of M3 submachine guns created by the need for interim production changes forced U.S. Army Ordnance workshops to fabricate pawl springs and other parts to keep existing weapons operational.^[14][18]
After its introduction to service, reports of unserviceability of the M3 commenced in February 1944 with stateside units in training, who reported early failure of the cocking handle/bolt retraction mechanism on some weapons.^[6] Similar reports later came from U.S. forces in Britain who were issued the M3.^[6] An investigation revealed several deficiencies in the construction of the M3’s bolt retraction mechanism, together with issues concerning barrel removal and retention as well as easily bent rear sights.^[6] As a result, several product improvements were incorporated into all new M3 production, including a new design retracting pawl with improved heat treatment, a new spring stop fitted to the right-hand brace of the retracting lever, a modified ejector featuring a cocking lever trip, a larger ratchet pad with improved heat treatment to more securely retain the barrel assembly, and strengthening gussets fitted to the sides of the fixed ‘L’ rear sight.^[6] After new complaints were raised about accidental magazine releases and failure of the wire buttstock to remain in place in the collapsed position, two additional changes were made to M3 production and approved by Ordnance on 31 August 1944.^[6]This included a small sheet metal guard around the magazine release button, and the inclusion of a stop between the two rods forming the wire stock at the butt end.^[6]
In December 1944, in response to field requests for further improvements to the basic M3 design, an improved, simplified variant of the M3 was introduced, the M3A1. 15,469 M3A1 submachine guns were produced before the end of World War II.^[6]
It was originally hoped that the M3 could be produced in numbers sufficient to cancel future orders for the Thompson submachine gun, and to allow the army to gradually withdraw the more expensive Thompson from front-line service. However, due to unforeseen production delays and requests for modifications, the M3 never fully replaced the Thompson during World War II, and purchases of the Thompson continued until February 1944. A total of 622,163 M3/M3A1 submachine guns of all types were assembled by the end of World War II, by which time the Thompson, at over 1.5 million guns produced, outnumbered the M3 and M3A1 in service by a factor of nearly three to one.^[6] The M3A1 did not see combat in World War II, but was used in Korea and Vietnam.^{[citation needed]}
The M3 and M3A1 were largely withdrawn from U.S. frontline service beginning in 1959 and into the early 1960s, but continued to be used until the mid-1990s as on vehicle equipment aboard armored vehicles. During the mid 1970s tank drivers of the 1st Battalion 67th Armored attached to the 2nd Armored Division were issued the M3A1, because of its size and portability.^{[citation needed]} During the Gulf War, drivers of the 19th Engineer Battalion attached to the 1st Armored Division were equipped with the M3A1 as part of their vehicle TOE.^{[citation needed]} It was also the initial submachine gun equipping the Delta Force who prized it for its impressively quiet performance when equipped with a silencer.^[19]

Design details[edit]

The M3 was an automatic, air-cooled blowback-operated weapon that fired from an open bolt. Constructed of plain .060-in. thick sheet steel, the M3 receiver was stamped in two halves that were then welded together.^[6] The M3 was striker-fired, with a fixed firing pin contained inside the bolt. The bolt was drilled longitudinally to support two parallel guide rods, upon which were mounted twin return (recoil) springs. This configuration allowed for larger machining tolerances while providing operating clearance in the event of dust, sand, or mud ingress.^[20] The M3 featured a spring-loaded extractorwhich was housed inside the bolt head, while the ejector was located in the trigger group.^[21] Like the British Sten, time and expense was saved by cold-swaging the M3’s barrel.^[6]

Operating mechanism[edit]

A diagram of the M3 illustrating function.

The M3 operating sequence is as follows: the bolt is cocked to the rear using the cocking handle located on the right side of the ejector housing. When the trigger is pulled, the bolt is driven forward by the recoil springs, stripping a round from the feed lips of the magazine and guiding the round into the chamber. The bolt then continues forward and the firing pin strikes the cartridge primer, igniting the round, resulting in a high-pressure impulse, forcing the bolt back against the resistance of the recoil springs and the inertial mass of the bolt. By the time the bolt and empty casing have moved far enough to the rear to open the chamber, the bullet has left the barrel and pressure in the barrel has dropped to a safe level. The M3’s comparatively low cyclic rate was a function of the relatively low pressure generated by the .45 ACP round, a heavy bolt, and recoil springs with a lighter-than-normal compression rate.^{[citation needed]}

Features[edit]

M3 receiver markings

The gun used metal stamping and pressing, spot welding and seam weldingextensively in its construction, reducing the number of man-hours required to assemble a unit. Only the barrel, bolt and firing mechanism were precision machined. The receiver consisted of two sheet metal halves welded together to form a cylinder. At the front end was a knurled metal cap which was used to retain the removable barrel. The cold-swaged, rifled barrel had 4 right-hand grooves. M3 and M3A1 submachine guns could be fitted with an optional, detachable flash hider, though none saw any service in World War II.^[22] A later production flash hider designated Hider, Flash M9 was produced in time to see service during the Korean War. It proved popular in combat, as frequent night engagements emphasized the need to reduce flash signatures on small arms. In Korea, U.S. soldiers equipped with automatic weapons were taught to look above the flash of their weapon during night firing, a tactic that sometimes prevented the detection of crawling enemy infiltrators and sappers.^{[citation needed]}
Projecting to the rear was a one-piece wire stock made from a formed steel rod that telescoped into tubes on both sides of the receiver. Both ends of the stock were tapped and drilled so that it could be used as a cleaning rod. It could also be used as a disassembly tool or as a wrench used to unscrew the barrel cap.^{[citation needed]}
The M3’s cocking handle assembly was located on the right-hand side of the receiver on the ejector housing, just forward and above the trigger, and consisted of nine parts.^[20] As the handle is pulled to the rear, a pawl rises to engage a notch in the bottom of the bolt, pushing the bolt to the rear until it locked back on the sear.
The fixed sights consisted of a rear aperture sight preset for firing at 100 yards (approximately 91 m) and a front blade foresight. All M3 submachine guns were test-fired for accuracy at a distance of 100 feet (30 m).^[6] With the sights set at six-o’clock on a bullseye target, each gun was required to keep four out of five shots within or cut the edge of a three-inch (76 mm) bulls’ eye to meet accuracy requirements.^[6]
The weapon’s only safety was the hinged ejection port dust cover. This cover had a projection on the underside that engaged a notch on the bolt, locking it in either its forward or rearmost positions. The M3 had no mechanical means of disabling the trigger, and the insertion of a loaded magazine would load the gun. With receiver walls made of relatively thin-gauge sheet metal, the M3/M3A1 were subject to disabling damage if dropped on an open dust cover – the covers bent easily, negating the safety feature. Dropping the gun on a sharp or hard surface could dent the receiver enough to bind the bolt.^{[citation needed]}
The M3/M3A1’s 30-round magazine was the source of complaints throughout the service life of the weapon.^[23][24] Unlike the Thompson, the M3 fed from a double-column, single-feed detachable box magazine which held 30 rounds and was patterned after the British Sten magazine; the single-feed design proved difficult to load by hand, and was more easily jammed by mud, dust, and dirt than double-column, double-feed designs like the Thompson.^[25] Additionally, the feed lips of the single-feed design proved more susceptible to feed malfunctions when slightly bent or damaged. Plastic dust caps were later issued to cover the feed end of the magazine and keep out dust as well as protect the sensitive feed lips.^{[citation needed]}

Variants[edit]

M3A1[edit]

In December 1944, a modernized version of the M3 known as the M3A1 was introduced into service, with all parts except the bolt, housing assembly, and receiver interchangeable with those of the M3. The M3A1 had several improvements:

• Most significantly eliminating the troublesome crank-type cocking lever assembly, replaced by a recessed cocking slot machined into the top front portion of the bolt, letting it be cocked by putting a finger into the cocking slot and pulling back the bolt.
• The retracting pawl notch was removed, and a clearance slot for the cover hinge rivets was added.
• The ejection port and its cover were lengthened to allow the bolt to be drawn back far enough to be engaged by the sear.
• The safety lock was moved further to the rear on the cover.
• To make loading the single-feed magazine easier, a magazine loading tool was welded to the wire stock; it also served as a cleaning rod stop.
• The barrel bushing received two flat cuts that helped in barrel removal by using the stock as a wrench.
• The barrel ratchet was redesigned to provide a longer depressing level for easier disengagement from the barrel collar.
• The spare lubricant clip (on the left side of the cocking lever assembly) was removed, replaced with an oil reservoir and an oiler in the pistol grip of the receiver assembly. The stylus on the oiler cap could also double as a drift to remove the extractor pin.

At 7.95 pounds empty, the M3A1 was slightly lighter than the M3, at 8.15 pounds empty, primarily due to the simplified cocking mechanism.^[6] The M3A1 was formally approved for production on 21 December 1944.^[6]
The M3A1 modifications resulted in a more reliable, lighter weight, easier to maintain, and easier to field strip submachine gun; the original M3 needed both the trigger guard removed and the cocking crank assembly detached from the receiver housing before unscrewing the barrel, but the M3A1 only required the user unscrew the barrel. To date, only one 9mm conversion kit for the M3A1 has been discovered.^[11]
Because it had already been issued in large numbers, the existing M3 magazine design was retained, despite demonstrated deficiencies exposed during the weapon’s firing trials and its early combat service.^[24] In an effort to improve reliability, a hard plastic Tenite cap designated T2 was adopted in November 1944 to fit over the feed lips of loaded magazines.^[25] These caps protected the feed lips while keeping out dirt, sand, and debris.^[26] Sometime during the 1960s the hard T2 plastic cap was replaced in service with one of pliant neoprene rubber, which could be removed with less noise.^[27] Unfortunately, during service in the humid climate of Vietnam it was discovered that the rubber cap caused rust to form on the covered portion of the magazine, while causing loaded ammunition to corrode.^[27]
Initially, M3 submachine guns returned for repair were not upgraded to the M3A1 standard, but merely inspected to ensure they had the improved M3 housing assembly and magazine release shield.^[28] During the Korean War, existing M3 guns in service were converted to the improved M3A1 configuration using additional new production parts.^[29] During the conversion, armorers frequently removed the M3 cocking handle, leaving the rest of the now-redundant cocking mechanism inside the subframe.^[30] Overall, the M3A1 was seen by most soldiers and Ordnance technicians as an improvement over the M3. However, complaints of accidental discharge continued to occur even as late as the Korean War.^[30] These incidents were sometimes caused by dropping the weapon on a hard surface with an impact sufficient to knock open the ejection port cover and propel the bolt backwards (but not enough to catch the sear). The return springs would then propel the bolt forward to pick up a cartridge from the magazine and carry it into the chamber, where the bolt’s fixed firing pin struck the primer upon contact.^[30][31]
In 1945, the Guide Lamp factory manufactured 15,469 M3A1 submachine guns before production contracts were canceled with the end of the war. During the Korean War, Ithaca Gun Co built another 33,000 complete guns as well as manufacturing thousands of parts for the repair and rebuilding of existing M3 and M3A1 weapons.^[32]

Foreign variants and derivatives[edit]

P.A.M. 1 & 2 (Argentina)[edit]

In 1954, a variant of the U.S. M3A1 submachine gun was designed at the Argentine FMAP (Fábrica Militar de Armas Portátiles) factory in the city of Rosario and put into production the following year as the P.A.M. 1 (Pistola Ametrelladora Modelo 1).^[33][34] Constructed of somewhat thinner-gauge steel than the U.S. M3A1, the P.A.M. 1 was in essence a 7/8 scale replica of the U.S. weapon in 9mm Parabellum caliber,^[35] but was lighter^[36] and had a higher rate of fire. This was due to an incomplete transfer of all details to Argentina.^[37] In service, the P.A.M. 1’s thinner sheet steel receiver tended to overheat with extended firing, while the gun itself proved somewhat more difficult to control in automatic fire despite the smaller caliber. Additionally, triggering the weapon to fire individual shots proved difficult owing to the increased rate of fire. Problems with accidental discharges and accuracy with the P.A.M. 1 led to an improved selective-fire version with a grip safety on the magazine housing known as the P.A.M. 2, first introduced in 1963.^[37]
Colloquially referred to as La Engrasadora (the Greaser), 47,688 P.A.M. 1 and P.A.M. 2 submachine guns were produced between 1955 and 1972. A number of P.A.M. 1 and P.A.M. 2 submachine guns were used by the Argentine Army during the Falkland Islands War with the United Kingdom in 1982, and captured examples were tested by British military forces.^[38]

Type 36 & 37 (China)[edit]

The Type 36 is a direct clone of the M3A1, manufactured in 1947 at the Shenyang Arsenal in Mukden.^[39] It resembles a M3A1, except that it has no flats to allow the use of a wrench for easy removal and it has no oil bottle trap in the pistol grip.^[39] Its parts are not interchangeable with the M3A1.^[39]
10,000 Type 36s were made before they were obtained by pro-Communist forces in 1949.^[39]
The Type 37 is a direct clone of the 9mm-chambered M3, made at the 60th Jinling Arsenal near Nanking.^[39] Production continued in Taiwan as the Type 39, a successor to the Type 37.^[39]

Users[edit]

Philippine Naval Special Warfare Group members conduct interdiction training with the U.S. Coast Guard in Cebu City, 2009. Two of them are armed with M3s.

•  Afghanistan^[40]
•  Argentina^[41]
•  Bolivia^[42]
•  Brazil^{[citation needed]}
•  People’s Republic of China: Copies made as the Type 36 and Type 37^[39]and used in the Korean War by Chinese soldiers.^[43]
•  Republic of China^[44]
•  Colombia: Used by the National Army of Colombia and the National Police of Colombia from the 1950s up to the 1970s, when it was replaced by the UZI submachine gun.^{[citation needed]}
•  Dominican Republic^{[citation needed]}
•  Ecuador^[42]
•  Greece Used by the Greek armed forces during World War II and the post-World War II period.^[2]
•  Grenada^[45]
•  Guatemala^[42]
•  Haiti^[46]
•  Japan: Used by the JSDF until the adoption of the Minebea PM-9.^[47][48][49] Known to be used by JGSDF tank crews as a personal defense weapon. Still used in limited numbers in certain branches of the JSDF.^[50]
•  Republic of Korea:^[42] Mainly used by Republic of Korea Army Special Warfare Command.
•  North Korea^{[51][unreliable source?]}
•  Macedonia: 707 surplus M3 submachine guns were transferred to Macedonia in 1999.^[42]
•  Mexico^{[citation needed]}
•  Morocco: 1,472 surplus M3A1 submachine guns were transferred to Morocco in the 1990s.^[52]
•  Philippine Commonwealth: Used by the Philippine Commonwealth Army, Philippine Constabulary and the Recognized Guerrillas during World War II under the Japanese Occupation from 1942 to 1945 and Post-War Era from 1945 to 1946.^{[citation needed]}
•  Philippines:^[42] Had their M3 submachine guns released from reserve stockpiles by the Philippine Navy for the Philippine Marine Corps‘s special forces due to budget constraints.^[53] Modifications done on the refurbished weapons include an integral suppressor and a Picatinny rail.^[54] The weapon had been tested with a prototype in May 2004.^[53]
•  United States^[1][42]
•  South Vietnam^[55][56]

Browning Machine Gun, Cal. .50, M2, HB
M2HB heavy machine gun
Type	Heavy machine gun
Place of origin	United States
Service history
In service	1933–present
Used by	See Users
Wars	World War II Indonesian National Revolution Korean War First Indochina War Suez Crisis Portuguese Colonial War Vietnam War Six-Day War Iran-Iraq war Yom Kippur War Lebanese Civil War Colombian Internal Conflict Cambodian Civil War Cambodian-Vietnamese War Falklands War South African Border War Invasion of Grenada Bougainville Civil War[1] Invasion of Panama Persian Gulf War Somali Civil War Yugoslav Wars Kosovo War War in Afghanistan[2] Iraq War Mexican Drug War Syrian Civil War[3] Iraqi Civil War (2014-present)[4] Yemeni Civil War (2015–present)[5] Saudi Arabian-led intervention in Yemen[6] Conflict in Najran, Jizan and Asir
Production history
Designer	John M. Browning
Designed	1918[7]
Manufacturer	Current: General Dynamics, Fabrique Nationale, U.S. Ordnance, and Manroy Engineering (UK) Former: Sabre Defence Industries, Colt’s Patent Fire Arms Company, High Standard Company, Savage Arms Corporation, Buffalo Arms Corporation, General Motors Corporation (Frigidaire, AC Spark Plug, Saginaw Steering, and Brown-Lipe-Chappin Divisions), Kelsey Hayes Wheel Company, Springfield Armory, Wayne Pump Company, ERMCO, and Ramo Manufacturing, Rock Island Arsenal
Produced	1921–present (M2HB)
No. built	3 million[8]
Specifications
Weight	38 kg (83.78 lb) 58 kg (127.87 lb) with tripodand T&E
Length	1,654 mm (65.1 in)
Barrel length	1,143 mm (45.0 in)
Cartridge	.50 BMG (12.7×99mm NATO)
Action	Short recoil-operated
Rate of fire	450-600 rounds/min (M2HB)[9][10] 750–850 rounds/min (AN/M2) 1,200-1,300 rounds/min (AN/M3)
Muzzle velocity	2,910 ft/s (890 m/s) for M33 ball
Effective firing range	1,800 m (2,000 yd)[9]
Maximum firing range	2,500 m (2,700 yd)
Feed system	Belt-fed (M2 or M9 links)

The M2 Machine Gun or Browning .50 Caliber Machine Gun is a heavy machine gun designed toward the end of World War I by John Browning. Its design is similar to Browning’s earlier M1919 Browning machine gun, which was chambered for the .30-06 cartridge. The M2 uses the much larger and much more powerful .50 BMG cartridge, which was developed alongside and takes its name from the gun itself (BMG standing for Browning Machine Gun). It has been referred to as “Ma Deuce”,^[11] in reference to its M2 nomenclature. The design has had many specific designations; the official 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 M2 has been produced longer than any other machine gun.
The Browning .50 caliber machine gun has been used extensively as a vehicle weapon and for aircraft armament by the United States from the 1930s to the present. It was heavily used during World War II, the Korean War, the Vietnam War, the Falklands War, the Iraq War and the War in Afghanistan in the 2000s and 2010s. It is the primary heavy machine gun of NATO countries, and has been used by many other countries as well. The M2 has been in use longer than any other firearm in U.S. inventory except the .45 ACP M1911 pistol, also designed by John Browning.
The current M2HB is manufactured in the U.S. by General Dynamics^[12] and U.S. Ordnance^[13] for use by the U.S. government, and for allies via Foreign Military Sales, as well as foreign manufacturers such as FN Herstal.

History[edit]

Machine guns were heavily used in World War I, and weapons of larger than rifle caliber were appearing. Both the British and French had large caliber machine guns. The larger rounds were needed to defeat the armor that was being introduced to the battlefield. Armor was also appearing in the skies. During World War I, the Germans introduced a heavily armored airplane, the Junkers J.I. The armor made aircraft machine guns using conventional rifle ammunition (such as the .30-06) ineffective.^[14]
Consequently, the American Expeditionary Force‘s commander General John J. Pershing asked for a larger caliber machine gun.^[15]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).^[14] U.S. Col. John Henry Parker, commanding a machine gun school in France, observed the effectiveness of a French 11 mm (0.43 in) incendiary armor-piercing round. The Army Ordnance Department ordered eight experimental Colt machine guns rechambered for the French 11 mm cartridge.^[16] The French 11 mm round was found to be unsuitable because its velocity was too low. Pershing wanted a bullet of at least 670 gr (43 g) and a muzzle velocity of 2,700 ft/s (820 m/s). Development with the French round was dropped.^[16]
Around July 1917, John M. Browning started redesigning his .30-06 M1917 machine gun for 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 wanted to use the cartridge in an anti-tank rifle, but Pershing insisted the cartridge be rimless.^[16] The first .50 machine gun underwent trials on 15 October 1918. It fired at less than 500 rounds per minute, and the muzzle velocity was only 2,300 ft/s (700 m/s). Cartridge improvements were promised.^[17] The gun was heavy, difficult to control, fired too slowly for anti-personnel, and was not powerful enough against armor.^[18]
While the .50 was being developed, some German T Gewehr 1918 anti-tank rifles and ammunition were seized. The German rounds had a muzzle velocity of 2,700 ft/s (820 m/s), an 800 gr (52 g) bullet, and could pierce ^{[clarification needed]}1 in (25 mm) at 250 yd (230 m).^[19] Winchester improved the .50 caliber round to have similar performance. Ultimately, the muzzle velocity was 2,750 ft/s (840 m/s).^[20]
Efforts by John M. Browning and Fred T. Moore resulted in the water-cooled Browning machine gun, caliber .50, M1921. An aircraft version was termed the Browning aircraft machine gun, caliber .50, M1921. These guns were used experimentally from 1921 until 1937. They had light-weight barrels and the ammunition fed only from the left side. Service trials raised doubts whether the guns would be suitable for aircraft or for anti-aircraft use. A heavy barrel M1921 was considered for ground vehicles.^[21]
John M. Browning died in 1926. Between 1927 and 1932, Dr. 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.^[22] FN Herstal (Fabrique Nationale) has manufactured the M2 machine gun since the 1930s.^[23] General Dynamics, U.S. Ordnance, and Manroy Engineering (UK) are other current manufacturers.^{[citation needed]}
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 121 lb (55 kg) with a water jacket, but the M2 HB weighs 84 lb (38 kg). Due to the long procedure for changing the barrel, an improved system was developed called QCB (quick change barrel). 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,^[24] readily replacing Browning’s own air-cooled .30 caliber machine gun design in nearly all American aircraft installations.

Design details[edit]

The Browning M2 is an air-cooled, belt-fed machine gun. The M2 fires from a closed bolt, operated on the short recoilprinciple. The M2 fires the .50 BMG cartridge, which offers long range, 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.
The M2 is a scaled-up version of John Browning’s M1917 .30 caliber machine gun, even using the same timing gauges.

Features[edit]

The M2 has varying cyclic rates of fire, depending on the model. The M2HB (heavy barrel) air-cooled ground gun has a cyclical rate of 450-575 rounds per minute.^[25] The early M2 water-cooled AA guns had a cyclical rate of around 450–600 rpm.^[26] The AN/M2 aircraft gun has a cyclic rate of 750–850 rpm; this increases to 1,200 rpm or more for AN/M3 aircraft guns fitted with electric or mechanical feed boost mechanisms.^[10] 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 or at less than 40 rounds per minute, or rapid fire for more than 40 rounds per minute. Slow and rapid firing modes use 5-7 round bursts with different lengths of pause between bursts.^[27]

A U.S. Marine mans a .50 caliber machine gun as part of a security force during a training exercise with the 24th Marine Expeditionary Unit in November 2002.

The M2 has an effective range of 1,830 metres (2,000 yd) and a maximum effective range of 2,000 metres (2,200 yd) when fired from the M3 tripod. In its ground-portable, crew-served role as the M2HB, the gun itself weighs 84 pounds (38 kg) and the assembled M3 tripod another 44 pounds (20 kg). In this configuration, the V-shaped “butterfly” trigger is located at the very rear of the weapon with a “spade handle” hand-grip 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 hand grips, 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.^[28] The upgraded M2A1 has a manual trigger block safety.

Twin M2HB machine gun during a Pre-aimed Calibration Fire (PACFIRE) exercise in May 2005

Because the M2 was intentionally 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. This will take a well trained individual less than two minutes to perform.
The charging assembly may be changed from left to right hand charge. A right hand charging handle spring, lock wire and a little know how are all that are required to accomplish this. The M2 can be battle ready and easily interchanged if it is preemptively fitted with a retracting slide assembly on both sides of the weapon system. This eliminates the need to have the weapon removed from service to accomplish this task.

Ammunition[edit]

M2 Browning on a Samson RCWSof the Israel Defense Forces

There are several different types of ammunition used in the M2HB and AN aircraft guns. From World War II through the Vietnam War, the big 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 0.875 inches (22.2 mm) of hardened steel armor plate at a distance of 100 yards (91 m) and 0.75 inches (19 mm) at 547 yards (500 m).^[29] 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.^[30]
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 1.34 inches (34 mm) of FHA (face-hardened steel plate) at 500 metres (550 yd), 0.91 inches (23 mm) at 1,200 metres (1,300 yd), and 0.75 inches (19 mm) at 1,500 metres (1,600 yd). This is achieved by using a 0.30-inch-diameter (7.6 mm) tungsten penetrator. The SLAP-T adds a tracer charge to the base of the ammunition. This ammunition was type classified in 1993.^[31][32]
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[edit]

An M2 fired from a rigid-hulled inflatable boat.

B-25H “Barbie III” showing four M2 feeds and 75 mm M5 gun

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 a sturdy pedestal mount. In later variants, twin and quadruple M2HB Brownings were used, such as the M45 Quadmount (aka “meat chopper”) used on the US 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.).
• Coaxial gun or independent mounting in some tanks.
• Fixed-mounted forward-firing primary aircraft armament (AN/M2 and AN/M3 light-barrel versions only). The AN/M2 was used as primary armament in almost all World War II U.S. pursuit aircraft (such as the North American P-51 Mustang, Republic P-47 Thunderbolt, Lockheed P-38 Lightning, Bell P-39 Airacobra, Curtiss P-40 Warhawk, Grumman F6F Hellcat and Vought F4U Corsair). It was also used in fixed mountings in bombers and ground attack aircraft like the Douglas SBD Dauntless dive bomber, Grumman TBF Avengertorpedo bomber, and medium bombers such as North American B-25 Mitchell, Martin B-26 Marauder and Douglas A-26 Invader. The later, faster-firing electrically feed-boosted AN/M3 was used in many Korean War-era U.S.A.F.fighter aircraft such as the Lockheed F-80 Shooting Star, Republic F-84 Thunderjet, North American F-86 Sabre, and early versions of the Martin B-57 Canberra bomber. The US Navy had largely completed their move to the (unrelated) M2/AN 20mm autocannon for aircraft armament by this time.
• Turret-mount or flexible-mounted defensive armament, again only with the AN/M2 light-barrel version, in almost all US World War II-era bombers and patrol aircraft such as the Boeing B-17 Flying Fortress, Consolidated B-24 Liberator and Boeing B-29 Superfortress heavy bombers, North American B-25 Mitchell and Marin B-26 Marauder medium bombers, Consolidated PBY Catalina patrol flying boats, Grumman TBF/TBM Avenger torpedo bombers, and in a combined offensive/defensive turret mounting in many Northrop P-61 Black Widow night fighters. The AN/M3 was used as a flexible, quad-mounted, radar-directed tail-defence gun as late as 1980 on the Boeing B-52 Stratofortress, until replaced by 20mm M61 Vulcan Gatling type cannon
• Variants of the AN/M3 are used as flexible door guns or as flexible remotely-controlled armament subsystems on many US Army, Navy, Marine Corps and Coast Guard helicopters, such as the Bell UH-1 Iroquois, Sikorsky UH-60 Blackhawk and variants, Sikorsky CH-53E Super Stallion, Bell OH-58 Kiowa and others.

United States[edit]

A U.S. soldier in Normandy stands guard with the M2HB installed on a dual-purpose mounting.

At the outbreak of the Second World War the United States had versions of the M2 in service as fixed aircraft guns, anti-aircraft defensive guns (on aircraft, ships, or boats), infantry (tripod-mounted) guns, and as dual purpose anti-aircraft and anti-vehicular weapons on vehicles.^[33][34]
The .50 AN/M2 light-barrel aircraft Browning used in planes had a rate of fire of approximately 800 rounds per minute, and was used singly or in groups of up to eight guns for aircraft ranging from the P-47 Thunderbolt to the B-25 Mitchellbomber, which in the last J-version of the Mitchell could have up to fourteen M2s firing forward for ground attack missions – eight in a solid metal-structure nose, four more mounted in a pair of conformal twin-gunned gun pods on the lower cockpit sides, and two more if the forward dorsal turret’s pair of M2 guns were also aimed straight forward.
In the dual-purpose vehicle mount, the M2HB (heavy barrel) 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,^[35] or perforate the hull plates and fuel tanks of a German half-track or light armored car.^[29][36][37] While the dual-purpose mounting was undeniably useful, it did normally require the operator to stand when using the M2 in a ground role, exposing him to return fire.^[38] Units in the field often modified the mountings on their vehicles, especially tanks and tank destroyers, to provide more operator protection in the anti-vehicular and anti-personnel role.^[39] 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.^[40][41] Vehicles would frequently “recon by fire” with the M2 Browning, i.e. they would fire continuously at suspected points of ambush while moving through areas still containing enemy forces. One vehicle would fire exclusively to the right, the following vehicle to the left, the next one to the right, and so on in order to cover both flanks of the advancing convoy.
Besides vehicle-mounted weapons, the heavy weapons companies in a World War II U.S. Army infantry battalion or regiment were each issued one M2 Browning with tripod (ground) mount.^[42] 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.^[43] Hearing the sound of an M2 could often cause enemy infantry to take cover.^[44] There are numerous instances of the M2 Browning being used against enemy personnel, particularly infantry assaults^[45] or for interdiction or elimination of enemy artillery observers or snipers at distances too great for ordinary infantry weapons.^[46][47][48]

An M2 overlooking the Korengal Valley at Firebase Phoenix, Afghanistan, in 2007

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.^[49] However, it was used by fast-moving motorized forces in the Philippines to destroy Japanese blocking units on the advance to Manila.^[43] The quad mount .50 was also used to destroy Japanese emplacements.^[50]
The M2HB was used in Korea and Vietnam, and later in both Operation Desert Storm, the Afghan theater of Operation Enduring Freedom and in Iraq. In 2003, U.S. Army SFC Paul Ray Smith used his M2HB mounted on an M113 armored personnel carrier to kill 20 to 50 enemies who were attacking a U.S. outpost, preventing an aid station from being overrun and allowing wounded soldiers to be evacuated,^[51] SFC Smith was killed during the firefight and was posthumously awarded the Medal of Honor.

M45 Quadmount[edit]

M45 .50 AA Quad aka the ‘Meat Chopper’

The M45 Quadmount was a mounting of four .50 M2HB guns with a single gunner situated behind an armored housing. This was used by U.S. AA battalions, fitted either on a towed trailer or mounted in a half-track carrier (M16 AA half-track). With 200 rounds per gun in a powered tracking mount, the guns proved very effective against low-flying aircraft. The use of four guns adequately compensated for the fact that the individual M2HB’s rate of fire (450-550 rounds per minute) was low for an effective anti–aircraft weapon.^[52]
Towards the end of the war, as Luftwaffe attacks became less frequent, the quad .50 (nicknamed the Meat Chopper or Krautmower^[52]) 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. Snipers firing from trees were engaged by the quad gunner at trunk level – the weapon would cut down and destroy the entire tree, and the sniper with it.^[44][50]
The M45 Quadmount was still in use during the Vietnam War.

Commonwealth and other forces[edit]

Australian M113 with twin mounted M1919 Browning and M2 Browning Quick Change Barrel machine guns.

Israel Defense Forces M2HQCB.

Commonwealth use of the M2 Browning .50 caliber machine gun (known as the .5 Browning in British and Commonwealth service) was limited 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. Nevertheless, the heavy Browning’s effectiveness was praised by many British and Commonwealth soldiers in infantry, armored, and ordnance branches.^[53][54] Many commanders thought that the .50 Browning the best weapon in its class, certainly the best of the American weapons, including the M1 Garand and M1 Carbine.^[54][55] In North Africa, after Commonwealth units began to obtain sufficient parts, manuals, gauges, and ammunition for the new weapon, the .50 Browning was increasingly used, eventually replacing the 15 mm Besa,^[54]but in Italy it was often deleted from top turret mountings because the mount exposed the operator to low branches and enemy fire.^[56] All LRDGs, and some SAS units used the aircraft (AN/M2) version of the gun, while beam/waist-mounted and turret-mounted Brownings were used later in the war in such aircraft as the Short Sunderland and Lancaster bomber.
After World War II, the .50 Browning continued to see action in Korea and other theaters, in aircraft, tripod (ground), ground AA (hip-ring), and vehicle mounts. One of its most notable actions in a ground role was in a fierce battle with a nine-man SAS team at the Battle of Mirbat in Oman in July 1972, where the heavy Browning and its API ammunition was used to help repulse an assault by 250 Yemeni Adoo guerrillas, though the more famous weapon from the battle is a 25 pounder gun.^[57]
A .50 caliber Browning was installed along with a .30 caliber Browning machine gun in each compact one-man turret on M113 APCs used by the Royal Australian Armoured Corps in South Vietnam.
The M2HB has been in service with the Israel Defense Forces since its establishment and has served in all of Israel‘s wars, operations and conflicts. In 2012 the IDF upgraded its M2HB machine guns to the M2HQCB model, with heavy quick change barrel.^[58] Today the M2 serves as an infantry crew-served heavy machine gun, as a remote-controlled external coaxial gun on Merkava main battle tanks, as the main weapon on the Samson RCWS and as a secondary weapons on Israeli Sea Corps gunboats and missile boats.
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

M2 as a sniper rifle[edit]

USMC M2 fitted with a Leupold CQBSS variable power scope.

The M2 machine gun has also been used as a long-range sniper rifle, when equipped with a telescopic sight. Soldiers during the Korean War used scoped M2s in the role of a sniper rifle, but the practice was most notably used by US Marine Corps sniper Carlos Hathcock during the Vietnam War. Using an Unertltelescopic 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 a standard-caliber sniper rifle of the time (a .30-06 Winchester Model 70). In fact, Hathcock set the record for the longest confirmed kill at 2,250 metres (2,460 yd), a recordwhich stood until 2002, when it was broken in Afghanistan by Canadian Army sniper Arron Perry.^[59][60]

Geneva Convention use misconception[edit]

It is often stated,^[61] sometimes even by military trainers,^[62] that it is illegal under the Geneva Convention to use the M2 against enemy personnel since it would cause “unnecessary suffering”. As such, most gunners supposedly aim for enemy troops’ belt buckles, since those are technically equipment and thus permissible targets. However, there is no provision of the Geneva Convention that has ever been interpreted to forbid the use of the M2 on personnel. The misconception may have arisen during the Korean or Vietnam Wars when U.S. troops were told to use their M2s only on enemy equipment due to shortages of ammunition.^[63] 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 equipment only, since the M40 was meant to be used against armor and firing the spotting gun at personnel would have given away the M40’s position before it could be used as intended, was mistakenly believed to apply to all weapons of that caliber and given legal justification.^[62]

Variants and derivatives[edit]

M2 variants[edit]

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An M2HB in the French Foreign Legion’s 2nd Infantry Regiment during an exercise.

Jungle Infantry soldier of the Brazilian Army mans an M2HB in the Amazon rainforest.

The basic M2 was deployed in U.S. service in a number of subvariants, all with separate complete designations as per the US Army system. The basic designation as mentioned in the introduction is Browning Machine Gun, Cal. .50, M2, with others as described below.
The development of the M1921 water-cooled machine gun which led to the M2, meant that the initial M2s were, in fact, water-cooled. These weapons were designated Browning Machine Gun, Cal. .50, M2, Water-Cooled, Flexible. There was no fixed water-cooled version.
Improved air-cooled heavy barrel versions came in three subtypes. The basic infantry model, Browning Machine Gun, Cal. .50, M2, HB, Flexible, a fixed developed for use on the M6 Heavy Tank designated Browning Machine Gun, Cal. .50, M2, HB, Fixed, and a “turret type” whereby “Flexible” M2s were modified slightly for use in tank turrets. The subvariant designation Browning Machine Gun, Cal. .50, M2, HB, TT was only used for manufacturing, supply, and administration identification and separation from flexible M2s.

M2HB heavy machine gun

A number of additional subvariants were developed after the end of World War II. The Caliber .50 Machine Gun, Browning, M2, Heavy Barrel, M48 Turret Type was developed for the commander’s cupola on the M48 Patton tank. The cupola mount on the M48A2 and M48A3 was thoroughly disliked by most tankers, as it proved unreliable in service.^[64] An externally mounted M2 was later adopted for the commander’s position on the M1 Abrams tanks. Three subvariants were also developed for use by the U.S. Navy on a variety of ships and watercraft. These included the Caliber .50 Machine Gun, Browning, M2, Heavy Barrel, Soft Mount (Navy) and the Caliber .50 Machine Gun, Browning, M2, Heavy Barrel, Fixed Type (Navy). The fixed types fire from a solenoid trigger and come in left or right hand feed variants for use on the Mk 56 Mod 0 dual mount and other mounts.

M2A1[edit]

M2E2 modification with quick-change barrel (QCB)

When the M2 was first being designed, John Browning faced two design challenges. With the machine tools available at that time, the dimensions that established the location of the bolt face and the depth of the chamber could not be held tightly enough to control the fit of the cartridge in the chamber. The round can be too tight in the chamber and the gun would not shoot, or be too loose in the chamber, resulting in a stoppage or ruptured cartridge. The other dimension that could not be held close enough was when the firing pin would fall. The solution to these problems was adjustable timing and headspace (“headspace” is the distance between the face of the bolt and the base of the cartridge case, fully seated in the chamber); the operator had to screw the barrel into the barrel extension, moving the barrel toward the bolt face to reach the proper headspace with simple gauges to allow the operator to adjust to the proper dimensions. By the late 20th century, the M2 was the only adjustable headspace weapon in the U.S. inventory. With rising reports of injuries from improperly headspaced weapons, the U.S. military held a competition for a quick change barrel conversion kit with fixed timing and headspace in 1997. Three companies offered kits and Saco Defense won the competition. However, funding was lost before the design could be fully evaluated and the program ended. In 2007, the military found money to start a new competition. Saco Defense had since been acquired by General Dynamics, which won the competition.^[65]

U.S. Army Ranger Special Operations Vehicle (RSOV) armed with RAMO M2HB-QCB machine gun

On October 15, 2010, the M2A1 heavy machine gun was type classified by the U.S. Army. Formerly known as the M2E2, the M2A1 incorporates improvements to the design including a quick change barrel (QCB) with removable carrying handle, a new slotted flash suppressor that reduces muzzle flash by 95 percent, fixed headspace and timing, a modified bolt, and a manual trigger block safety. “Timing” is the adjustment of the gun so that firing takes place when the recoiling parts are in the correct position for firing. When a standard M2 had a barrel change, the headspace and timing had to be manually set. Improper adjustment could damage the weapon and cause serious injury to the user. Fixed headspace and timing reduces risk, and the carrying handle allows the barrel to be switched in seconds.^[66][67] In June 2011, the Army began conversion of M2HB machine guns to M2A1s.^[68] The M2A1 was named one of the greatest Army inventions of 2011.^[69] As of November 30, 2012, 8,300 built or converted M2A1s had been fielded by the U.S. Army; the program will upgrade the Army’s entire M2 inventory of more than 54,000 guns.^[70] The U.S. Marine Corps plans to upgrade all of their ground-mounted M2s to M2A1 standard from 2016 to 2018.^[71] The first phase of conversions was completed in March 2017, with 3,600 M2A1s planned to be fielded by the Marines in total.^[72] The Israel Defense Forces adopted the M2-HQCB (the commercial version of the M2A1) in 2012 as a replacement to the M2HB.^[73]

Aircraft guns[edit]

AN/M2[edit]

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P-47 firing its eight M2 .50 machine guns during night gunnery

The M2 machine gun was widely used during World War II, and in later postwar conflicts, as a remote or flexible aircraft gun. For fixed (offensive) or flexible (defensive) guns used in aircraft, a dedicated M2 version was developed called the .50 Browning AN/M2. The “AN” stands for “Army/Navy”, since the gun was developed jointly for use by both services (unusual for the time, when the delineations between the Army and Navy were much stricter, and relations between armed services were often cool, if not outright hostile^{[citation needed]}). The AN/M2 had a cyclic rate of 750–850 rounds per minute, with the ability to be fired from an electrically operated remote-mount solenoid trigger when installed as a fixed gun. Cooled by the aircraft’s slip-stream, the air-cooled 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),^[74] which also had the effect of increasing the rate of fire. The official designation for this weapon was Browning Machine Gun, Aircraft, Cal. .50, AN/M2 (Fixed) or (Flexible). The B-17G Flying Fortressheavy bomber was armed with up to 13 AN/M2 guns in both turreted and flexible positions, with only the later versions of the B-25J Mitchell medium bomber, field-fitted with solid metal noses carrying more AN/M2 guns. These could carry from 14 to 18 M2s, mostly aimed forward for attack duties, including two guns on the forward-located dorsal turret of the B-25H and J models.

M296[edit]

The XM296/M296 is a further development of the AN/M2 machine gun for the OH-58 Kiowa Warrior helicopter. The M296 differs from previous remote firing variants in that it has adjustable firing rate (500–850 rpm), while lacking a bolt latch (allowing single-shot operation).^[75] As an air-cooled gun used aboard a relatively slow rotary-wing aircraft, the M296 has a burst restriction rate of 50 rounds per minute sustained fire or 150 rounds per minute maximum while conducting peacetime training requirements; the combat firing rate is unrestricted but a ten-minute cooling period after prolonged firing is mandated to avoid stoppages due to overheating.^[76]

XM213/M213, XM218, GAU-15/A, GAU-16/A, and GAU-18/A[edit]

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The XM213/M213 was a modernization and adaptation of existing .50 caliber AN/M2s in inventory for use as a pintlemounted door gun on helicopters using the M59 armament subsystem.
The GAU-15/A, formerly identified as the XM218, is a lightweight member of the M2/M3 family. The GAU-16/A was an improved GAU-15/A with modified grip and sight assemblies for similar applications. Both of these weapons were used as a part of the A/A49E-11 armament subsystem (also known as the Defensive Armament System).
The GAU-18/A, is a lightweight variant of the M2/M3, and is used on the USAF’s MH-53 Pave Low and HH-60 Pave Hawkhelicopters. These weapons do not use the M2HB barrel, and are typically set up as left-hand feed, right-hand charging weapons, but on the HH-60 Pavehawks that use the EGMS (External Gun Mount System) the gun is isolated from the shooter by a recoil absorbing cradle and all weapons are set up as right hand charge but vary between left and right hand feed depending on what side of the aircraft it is on. A feed chute adapter is attached to the left or right hand feed pawl bracket allowing the weapon to receive ammunition through a feed chute system connected to externally mounted ammunition containers holding 600 rounds each.

AN/M3, GAU-21/A, and M3P[edit]

A German Army ramp gunner mans an M3M on board a CH-53 helicopter

During World War II, a faster-firing Browning was developed for aircraft use. The AN/M3 features a mechanical or electrically boosted feed mechanism to increase the rate of fire to around 1,200 rounds per minute. The AN/M3 was used in Korea on the F-82 Twin Mustang (the XP-82 mounted a total of 14 AN/M3 machine guns), F-86 Sabre, F-84 Thunderjet and F-80 Shooting Star, and in Vietnam in the XM14/SUU-12/A gun pod. Today, it can be found on the Embraer EMB 314 Super Tucano.
The M3-series is used by the U.S. military in two versions; the M3M and M3P. The fixed, remote-firing version, the FN M3P, is employed on the Avenger Air Defense System, and is currently used on the OH-58D, augmenting the XM296 .50 cal. machine gun.^[77] The M3M flexible machine gun has been adopted by USN under the designation GAU-21/A for use on helicopters. The GAU-21/A is also being used by the U.S. Marine Corps to upgrade from the XM-218/GAU-16 .50 cal. machine gun for the CH-53E,^[78] on the UH-1Y Venom, and on the Canadian Forces’ CH-146 Griffon via the INGRESS upgrade.^{[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 use of a soft mount.^[79]

Users[edit]

The M2 family has been widely used abroad, primarily in its basic infantry configuration. A brief listing of designations for M2 family weapons follows:

Country	NATOMember	Designation	Description
Argentina[80]	No	M2HB	12.7 × 99 mm Browning M2HB machine gun
Australia[80]	Global Partner	M2HB-QCB[81]
Austria[80]	No	üsMG M2
Bahamas[80]
Bahrain[82](p77)
Belgium[80]	Yes
Benin[80]	No
Bolivia[80]
Brazil[80]		Mtr .50 M2 HB “BROWNING”
Bulgaria[80]	Yes
Burkina Faso[80]	No
Bosnia[80]
Burundi[80]
Cameroon[80]
Canada[80]	Yes	FN M2HB-QCB, GAU-21
Chad[80]	No
Chile[80]
Colombia[80]
Cote d’Ivoire[80]
Croatia[80]	Yes
Democratic Republic of Congo[80]	No
Denmark[80]	Yes	M/50 TMG
		M/2001 TMG	12.7 × 99 mm FNH M2HB-QCB[83]
		?	12.7 × 99 mm FNH M3M machine gun[84]
Cyprus
Czech Republic[80]	Yes		12.7 × 99 mm FNH M2HB-QCB[85]
Djibouti[80]	No		12.7 × 99 mm Browning M2HB machine gun
Dominican Republic[80]
Ecuador[80]
Egypt[80]
El Salvador[80]
Estonia[86]	Yes	Browning M2 sometimes as Raskekuulipilduja Browning M2	12.7 × 99 mm Browning M2HB. Usually mounted on vehicles, such as the Pasi XA-180 and XA-188, but the tripod version is also in use.
Ethiopia[80]	No		12.7 × 99 mm Browning M2HB machine gun
France[80]	Yes
Finland[87]	No	12,7 RSKK 2005	12.7 × 99 mm Browning M2HB machine gun in Protector remote weapon stations in Patria AMVAPCs.[88]
Gabon[80]			12.7 × 99 mm Browning M2HB machine gun
Gambia[80]
Ghana[80]
Germany[89]	Yes	M3M, MG50
Greece[80]
Guatemala[80]	No
Honduras[80]
Hungary[citation needed]	Yes
India[80]	No
Indonesia[80]
Iran[80]
Iraq		No
Ireland[80]		.5 Heavy Machine Gun (HMG)[90]
Israel[80]	No	מק”כ 0.5	12.7 × 99 mm M2HB-QCB, used by all ground forces (infantry, armored fighting vehicles and tanks) and naval forces
Italy[80]	Yes		12.7 × 99 mm Browning M2HB machine gun
Jamaica[80]	No
Japan[80]		12.7mm Heavy Machine Gun M2
Jordan[80]
Katanga
South Korea[80]		K6 (standard HMG), MG50 (being phased out), M3M (used by Cheonghae Unit[91])	12.7 × 99 mm Browning M2HB with additional modification; licensed by Yeohwa Shotgun
Kuwait[80]			12.7 × 99 mm Browning M2HB machine gun
Lebanon[80]
Liberia[80]
Libya[citation needed]	No
Latvia[92]	Yes	M2HB-QCB
Lithuania[93]
Luxembourg[80]		Mitrailleuse .50 M2 HB[94]
Madagascar[80]	No
Malaysia[80]
Mauritania[80]
Mauritius[80]
Mexico[80]
Morocco[80]
Myanmar[80]
Namibia	No
Netherlands[80]	Yes
New Zealand[80]	Global Partner
Nicaragua[80]	No
Niger[80]
Nigeria[80]
Norway[80]	Yes	12,7 mitraljøse
Oman[80]	No
Pakistan[80]
Panama[80]
Paraguay[80]
Peru[80]
Philippines[80]
Portugal[80]	Yes
Qatar[80]	No
Romania[80]	Yes
Rwanda[80]	No
Saudi Arabia[80]
Senegal[80]
Serbia[80]
Singapore[80]
Somalia[80]
South Africa[80]		50 Browning
Soviet Union	No	M2 AA variant, Lend-Lease, 3100 pieces[95]
Spain[80][96]	Yes	M2HB-QCB, M3M
Sweden[97]	No	Kulspruta 88 (Ksp 88)
Switzerland[80]		MG 64
Taiwan[80]
Thailand[80]
Togo[80]
Tonga[80]
Tunisia[80]
Turkey[80]	Yes
Turkmenistan[98]	No
United Arab Emirates[80]
United Kingdom[80]	Yes	L2A1
		L6, L6A1	12.7 × 99 mm Browning M2HB machine gun; ranging gun for the L7 105 mm tank gun on the Centurion tank
		L11, L11A1	12.7 × 99 mm Browning M2HB machine gun; ranging gun
		L21A1	12.7 × 99 mm Browning M2HB machine gun; ranging gun for the 120 mm tank gun on the Chieftain tank
		L111A1[99]	12.7 × 99 mm M2QCB machine gun
		M3M[100]	12.7 × 99 mm Browning M2HB machine gun; Upgraded M2 for use on Commando Helicopter Force and other units as helicopter door guns.
United States[80]		Browning Caliber .50 M2, M2HB, XM218/GAU-16, GAU-21	12.7 × 99 mm Browning M2HB machine gun
Uruguay[80]	No		12.7 × 99 mm Browning M2HB machine gun
Venezuela[80]
Yemen[80]
Zimbabwe[80]