It features Gatling-style rotating barrels with an external power source, normally an electric motor. Even after Gatling slowed down the mechanism, the new electric-powered Gatling gun had a theoretical rate of fire of 3,000 rounds per minute, roughly three times the rate of a typical modern, single-barreled machine gun. In the 1960s, the United States Armed Forces began exploring modern variants of the electric-powered, rotating barrel Gatling-style weapons for use in the Vietnam War.
The "Mini" in the name is in comparison to larger caliber designs that use a rotary barrel design, such as General Electric's earlier 20-millimeter M61 Vulcan, and "gun" for the use of rifle caliber bullets as opposed to autocannon shells. American forces in the Vietnam War, 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.
Versions are designated M134 and XM196 by the United States Army, and GAU-2/A and GAU-17/A by the U. Gatling later replaced the hand-cranked mechanism of a rifle-caliber Gatling gun with an electric motor, a relatively new invention at the time. Of those, the best-known today is perhaps the Fokker-Leimberger, an externally powered 12-barrel rotary gun using the 7.92×57mm Mauser round; it was claimed to be capable of firing over 7,000 rpm, but suffered from frequent cartridge-case ruptures None of these German guns went into production during the war, although a competing Siemens prototype (possibly using a different action) which was tried on the Western Front scored a victory in aerial combat.
The ancestor to the modern minigun was a hand cranked mechanical device invented in the 1860s by Richard Jordan Gatling. During World War I, several German companies were working on externally powered guns for use in aircraft.
The term is sometimes used loosely to refer to guns of similar rates of fire and configuration regardless of power source and caliber.
"Minigun" refers to a specific model of weapon that General Electric originally produced, but the term "minigun" has popularly come to refer to any externally powered rotary-style gun of rifle caliber.
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.
In order to develop a weapon with a more reliable, higher rate of fire, General Electric designers scaled down the rotating-barrel 20 mm M61 Vulcan cannon for 7.62×51mm NATO ammunition.
The resulting weapon, designated M134 and known popularly as the Minigun, could fire up to 6,000 rounds per minute without overheating. selectable rate of fire specified to fire at rates of up to 6,000 rpm with most applications set at rates between 3.000-4,000 rounds per minute.
The Minigun was mounted on Hughes OH-6 Cayuse and Bell OH-58 Kiowa side pods; in the turret and on pylon pods of Bell AH-1 Cobra attack helicopters; and on door, pylon and pod mounts on Bell UH-1 Iroquois transport helicopters.
Several larger aircraft were outfitted with miniguns specifically for close air support: the Cessna A-37 Dragonfly with an internal gun and with pods on wing hardpoints; and the Douglas A-1 Skyraider, also with pods on wing hardpoints. government had procured some 10,000 miniguns during the Vietnam War.
Other famous gunship airplanes were the Douglas AC-47 Spooky, the Fairchild AC-119, and the Lockheed AC-130. By 1975, production of spare parts had ceased with the Army in possession of a large inventory.