Very few machine guns in the history of the world own a legacy such as that of the famous Browning M2 heavy machine gun series. Born out of a World War 1 requirement of 1918 which saw American authorities attempt to copy the success of the French Hotchkiss M1914 11mm medium machine gun for the anti-aircraft role, engineers John Browning and Fred Moore went to work on developing a large-caliber version of their existing M1917 .30-06 caliber machine gun. The resulting effort became the "US Machine Gun, Caliber .50, M1921" of 1921 chambered for the mammoth 12.7mm cartridge.
Debuting well past the war in 1921 (the war had ended in 1918), the new machine gun was classified as a "heavy machine gun" and operated from the "short recoil" principle through a closed bolt function. It was initially a water-cooled weapon system which allowed for long-running bursts of fire and used to prevent the barrel from overheating (this obviously requiring a consistently cool water supply to be used). The weapon was chambered for the .50 BMG ("Browning Machine Gun") cartridge (otherwise known as the 12.7x99mm NATO in the post-WW2 world) and fed via an ammunition belt running through the upper receiver. The .50 BMG was itself a massive cartridge shaped like a traditional bullet and featuring a rimless bottleneck casing. It was also debuted in 1921 and attributed to the Winchester Repeating Arms Company, a firm which John Browning partnered with in the years prior to his collaboration with the Belgian firm of Fabrique Nationale. The weapon/cartridge combination went on to become one of the most lethal, ferocious weapon systems of all time, seeing use within dozens of national armies and irregular forces around the world through countless notable conflicts. With the water jacket and water-cooling system in place, the M2 weighed in at 121lbs and rate of fire was approximately 450 to 600 rounds per minute.
Once in operational service, the design was furthered to produce the improved "M1921A1" designation under the Colt brand (John Browning had died in Belgium in 1926, his existing work being carried on by others). It was not until the 1930s that a new Browning machine gun mark was released in the form of the "Browning M2" though this early form still utilized water-cooling for the barrel but instituted a new water circulation system along the barrel jacket. Large-scale Browning machine gun production was undertaken by Colt beginning in 1933. In the same decade (leading up to World War 2), an air-cooled variant was developed for use in aircraft and this, too, was confusingly designated as the "Browning M2". It would be this production form that would become the definitive entry in the Browning heavy machine gun line.
While the air-cooled version proved capable of firing the .50 BMG cartridge, it could not manage firing beyond 75 rounds before overheating the barrel to the point of fracture. An attempt to rectify the issue produced the M2HB ("Heavy Barrel") guise and this form was applicably given a stronger barrel assembly to help dissipate the inherent heat build-up. This made for a heavier weapon system (84lbs) but a weapon that could nonetheless be fired for longer periods of time. To help further relieve the barrel heating issue, a "quick change" function was added to the barrel assembly allowing an operator to replace the heated barrel with a cool one (this function came to be known as QCB - "Quick Change Barrel").
The M2 ultimately proliferated the American military inventory prior to and during World War 2. It was utilized in all manner of ways as a defensive and offensive offering. The type served in fixed and flexible mountings within fighter and bomber aircraft of the US Army Air Force (as the AN/M2) while also being the weapon of choice in combat vehicles including tanks. The machine gun functioned extremely effectively in the anti-aircraft/anti-armor role and could decimate personnel unfortunate enough to cross its firing path. Specialized vehicles mounting multiple Browning heavy machine guns in traversing turret mounts were produced as ad hoc anti-aircraft/anti-infantry measures as the war progressed. The weapon could further be implemented as an infantry fire support measure for suppression fire though this required multiple crew to manage its cumbersome operation (gunner, ammunition handler, transport crew). The M2 was further installed as an anti-aircraft measure on countless naval ships without loss of effectiveness. Range was out to 2,000 yards though targets could be reached as far out as 2,200 yards with some care (and sometimes a bit of luck). Muzzle velocity was rated at 2,900 feet per second, providing for excellent penetration values at range. Aircraft versions could achieve 800 to 1,200 rounds per minute.
The M2 also saw widespread use during the war by Britain and her Commonwealth nations including Australia, Canada, South Africa and New Zealand. These were employed in similar ways and with great success to the point that the Browning design largely replaced the British BESA series machine guns then in use. In the British Army nomenclature, the weapon received the L2A1, L6, L11, LO21, L111 and M3M designations to mark their various types in service. The Soviet Army received some 3,100 M2s through Lend-Lease during the war.
After the war, the M2 maintained a very healthy existence and saw use through an increasing user base the world over. After World War 2, the M2 was in combat with American forces once again during the Korean War of the early 1950s as well as during the Vietnam War of the 1950s, 1960s and 1970s. It also went on to see extensive actions in other notable wars elsewhere and in less publicized conflicts. In some instances, troopers found the M2 suitable for the long-range sniper role and modified their M2s with appropriate optics. This modification was used to good effect in the Vietnam War by US Marine Carlos Hathcock (1942-1999).
Despite its World War 1 origins, the excellent Browning M2 remains in widespread use today and is/has been produced by General Dynamics and US Ordnance in the United States as well as Fabrique National in Belgium and Manroy Engineering of the UK. It is estimated that some 3 million M2 units have been manufactured since 1921. Many of the newer generation heavy machine guns developed by US allies owe much to the tried-and-true design that was the M2 Browning developed by master gunsmith John Browning and proven by war.
Beyond World War 2, Korea and Vietnam, the M2 has been featured in the 1st Indochina War, the Suez Crisis, the Six Day War, the Yom Kipper War, the Cambodian Civil War, the Cambodian war with Vietnam, the Falklands War, the South African Border War, the US invasion of Panama, the 1991 Gulf War, the Somali Civil War of the 1990s, the Yugoslav Wars, the 2001 US invasion of Afghanistan and, most recently, in the 2003 US invasion of Iraq.
The M2HB's formal designation is "Browning Machine Gun, Caliber .50, M2, HB". The HB model has seen service since 1933.
The .50 BMG (12.7x99mm NATO) cartridge has proven useful in the long-range sniper role when utilized in anti-material rifle guises. This is embodied perfectly by the Barrett series of heavy rifles deployed by the United States and others. The anti-material rifle has since become a standardized part of many armies around the world for its effectiveness in dealing with enemy personnel and armor at range.
In October of 2010, the US Army formally created the M2A1 designation in response to an improved form of the M2 Browning. The M2A1 initiative was born out of the failed XM806 program of 2012, a General Dynamics heavy-caliber (50 BMG) development being considered for replacing the original Browning design. The M2A1 brings about use of a new flash suppressor, revised bolt assembly, manual trigger block safety, a Quick-Change Barrel (QCB) feature and an optional carrying handle. Existing US Army M2HB machine guns will undergo the modification to the new M2A1 standard which number some 45,000 individual units.