The Minigun is a 7.62 mm, multi-barrel heavy machine gun with a high rate of fire (2,000 to 6,000 rounds per minute), employing Gatling-style rotating barrels with an external power source. In popular culture, the term "Minigun" has come to refer to any externally-powered Gatling gun of rifle caliber, though the term is sometimes used to refer to guns of similar rates of fire and configuration, regardless of power source and caliber. Specifically, minigun refers to a single weapon, originally produced by General Electric. The "Mini" of the name is in comparison to designs that use a similar firing mechanism but larger shells, such as General Electric's earlier 20 mm M61 Vulcan.
In the 1960s, the United States armed forces began exploring modern variants of the electric-powered, rotating barrel Gatling gun-style weapons for use in the Vietnam War. The US forces in Vietnam, which used helicopters as one of the primary means of transporting soldiers and equipment through the dense jungle, found that the thin-skinned helicopters were very vulnerable to small arms fire and rocket-propelled grenade (RPG) attacks when they slowed down to land. Although helicopters had mounted single-barrel machine guns, using them to repel attackers hidden in the dense jungle foliage often led to barrels overheating or cartridge jams.
USAF helicopter crewman in Vietnam firing a minigun in 1968In order to develop a weapon with a more reliable, higher rate of fire, General Dynamics designers scaled down the rotating-barrel 20 mm M61 Vulcan cannon for 7.62×51 mm NATO ammunition. The resulting weapon, designated M134 and known popularly as the Minigun, could fire up to 4,000 rounds per minute without overheating. (Originally, the gun was specified at 6,000 rpm, but this was later lowered to 4,000). The Minigun was mounted on OH-6 Cayuse and OH-58 Kiowa side pods, in the turret and wing pods on AH-1 Cobra attack helicopters, on door, pylon and pod mounts on UH-1 "Huey" Iroquois transport helicopters, and on many other helicopters including the H-53 (MH-53 Pave Low) and the common H-60 family (UH-60 Black Hawk, HH-60 Pave Hawk, etc.)Several larger aircraft were outfitted with miniguns specifically for close air support: the A-37 Dragonfly with an internal gun and with pods on wing hardpoints, and the A-1 Skyraider also with pods on wing hardpoints. Other famous gunship airplanes were the AC-47 Spooky, the AC-119 gunship, and the AC-130 gunship.
