M134 Minigun

The ancestor to the modern minigun was a hand cranked mechanical device invented in the 1860s by Richard Jordan Gatling. He later replaced the hand-cranked mechanism of a rifle-caliber Gatling gun with an electric motor, a relatively new invention at the time. Even after Gatling slowed 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. Gatling's electric-powered design received U.S. Patent #502,185 on July 25, 1893.[3] Despite his improvements, the Gatling gun fell into disuse after cheaper, lighter-weight, recoil and gas operated machine guns were invented; Gatling himself went bankrupt for a period.[4]

During World War I, several German companies were working on externally powered guns for use in aircraft. 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[5] due to its "nutcracker" rotary split-breech design, which is fairly different from that of conventional rotary gun designs.[6] 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.[5] The British also experimented with this type of split-breech during the 1950s, but they were also unsuccessful.[7]

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. 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 to land. Although helicopters had mounted single-barrel machine guns, using them to repel attackers hidden in the dense jungle foliage often led to overheated barrels or cartridge jams.[8][9]

A U.S. Air Force rotary-wing crewman fires a minigun during the Vietnam War.

To develop a more reliable weapon with a higher rate of fire, General Electric designers scaled down the rotary-barrel 20 mm M61 Vulcan cannon for 7.62×51mm NATO ammunition. The resulting weapon, designated M134 and known as the "Minigun", could fire up to 6,000 rounds per minute without overheating. The gun has a variable (i.e. selectable) rate of fire, specified to fire at rates of up to 6,000 rpm with most applications set at rates between 3,000 and 4,000 rounds per minute.

View of M134 from inside a UH-1 Huey, Nha Trang AB, 1967

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. Other famous gunship airplanes are the Douglas AC-47 Spooky, the Fairchild AC-119, and the Lockheed AC-130.[9]

The U.S. government had procured some 10,000 Miniguns during the Vietnam War.[10] Around 1990, Dillon Aero acquired a large number of Miniguns and spares from "a foreign user". The guns kept failing to shoot continuously, revealing that they were actually worn-out weapons. The company decided to fix the problems encountered, rather than simply putting the guns into storage. Fixing failure problems ended up improving the Minigun's overall design. Word of Dillon's efforts to improve the Minigun reached the 160th SOAR, and the company was invited to Fort Campbell, Kentucky, to demonstrate its products. A delinker, used to separate cartridges from ammunition belts and feed them into the gun housing, and other parts were tested on Campbell's ranges. The 160th SOAR were impressed by the delinker's performance and began ordering them by 1997. This prompted Dillon to improve other design aspects including the bolt, housing and barrel. Between 1997 and 2001, Dillon Aero was producing 25–30 products a year. In 2001, it was working on a new bolt design that increased performance and service life. By 2002, virtually every component of the minigun had been improved, so Dillon began producing complete weapons with improved components. The guns were purchased quickly by the 160th SOAR as its standardized weapon system. The gun then went through the Army's formal procurement system approval process, and in 2003 the Dillon Aero minigun was certified and designated M134D.[10] Once the Dillon Aero system was approved for general military service, Dillon Aero GAU-17s entered Marine Corps service and were well received in replacing the GE GAU-17s serving on Marine UH-1s.[11]

The core of the M134D was a steel housing and rotor. To focus on weight reduction, a titanium housing and rotor were introduced, creating the M134D-T which had reduced weight from 62 lb (28 kg) to 41 lb (19 kg). The gun housing had a 500,000-round lifespan before it wore out, which was far higher than a conventional machine gun's 40,000-round lifespan but lower than that of other rotary guns. A hybrid of the two weapons resulted in the M134D-H, which had a steel housing and titanium rotor. It was cheaper with the steel component and only 1 lb (0.45 kg) heavier than the M134D-T, and restored its lifespan to 1.5 million rounds.[10][12] The M134D-H is currently in use on various 160th Regiment platforms.[10]

Dillon also created specialized mounts and ammunition-handling systems. Initially, mounts were made only for aviation systems. Then from 2003 to 2005, the Navy began mounting Dillon miniguns on specialized small boats. In 2005, the Naval Surface Warfare Center Crane Division procured guns to mount on Humvees. In Iraq, US Army Special Forces units on the ground were frequently engaged by opposition forces, so they mounted M134D miniguns on their vehicles for additional firepower. After several engagements the attackers seemed to avoid vehicles with miniguns. Later, the Special Forces units began concealing their weapons so opposition troops would not know they were facing the weapon; the regular Army units did the opposite, creating minigun mock-ups out of painted PVC pipes tied together to resemble barrels to intimidate enemies.[10]

Garwood Industries created the M134G version with several modifications to the original GE system. The optimum rate of fire was determined by Garwood to be around 3,200 rounds per minute (rpm). The M134G is being produced with this firing rate as well as 4,000 rpm and the previous standard 3,000 rpm rate.[13] Garwood Industries made several other modifications to the 1960s Minigun design in order to meet modern-day military and ISO standards.[13] This includes modifications to the drive motor, feeder and barrel clutch assembly.[14]

From 2015 to 2017 Garwood Industries CEO Tracy Garwood collaborated with firearms dealer Michael Fox and weapons smuggler Tyler Carlson to supply miniguns to Mexican drug cartels. Garwood submitted false paperwork to the ATF claiming that some M134G rotor housings had been destroyed when they were actually sold to the gun-running ring. In 2017 federal agents raided Fox's home and recovered two of the rotor housings that Garwood had reported destroyed. A number of the rotor housings were shipped to Mexico and a completed M134G using a reportedly destroyed rotor housing was recovered from a cartel by Mexican law enforcement.[15] Garwood claimed he did not know that the intended buyers were Mexican cartels although he was aware that they were to be used for illegal activity.[16]

SUU-11/A pod in the cargo door of an AC-47

One of the first applications of the weapon was in aircraft armament pods. These gun pods were used by a wide variety of fixed- and rotary-wing aircraft mainly during the Vietnam War, remaining in inventory for a period afterward. The standard pod, designated SUU-11/A by the Air Force and M18 by the U.S. Army, was a relatively simple unit, completely self-contained, with a 1,500-round magazine directly feeding delinked ammunition into the weapon. This means the Minigun fitted to the pod does not require the standard MAU-56/A delinking feeder unit.[30] A number of variants of this pod exist.

Initially on fixed-wing gunships such as the Douglas AC-47 Spooky and Fairchild AC-119, the side-firing armament was fitted by combining SUU-11/A aircraft pods, often with their aerodynamic front fairings removed, with a locally fabricated mount. These pods were essentially unmodified, required no external power, and were linked to the aircraft's fire controls. The need for those pods for other missions led to the development and fielding of a purpose-built "Minigun module" for gunship use, designated the MXU-470/A. These units first arrived in January 1967 with features such as an improved 2,000-round drum and electric feeder allowing simplified reloading in flight. The initial units were unreliable and were withdrawn almost immediately.[31] By the end of the year, the difficulties had been worked out and the units were again being fitted to AC-47s, AC-119s, and AC-130s, with a specific ammunition load that replaced every fifth 'ball' round with a tracer round to enable better accuracy by the gunners, and also earning these airborne gunships the nickname 'Puff the Magic Dragon' by the Viet Cong due to their apparent ability of spitting fire and making everything they hit disappear or die. The AC-47 had three side mounted MXU-470/As (four were mounted on its replacement, the AC-119) and when all firing at once created a devastating image in the eyes of the enemy. The first AC-130A Gunship IIs did away with the MXU-470/A mounts and instead used GAU-2/As, and not only had four 7.62mm GAU-2/A minigun mounts, but added four 20mm M61 Vulcan 6-barrel rotary cannons; this configuration was upgraded two years later in 1969 by removing two each of the GAU-2/As and M61s and adding two 40mm (1.58 in) L/60 Bofors cannons in the aptly named AC-130A 'Surprise Package'. This configuration lasted two more years until, in late 1971, the AC-130E Pave Aegis arrived, which did away with the miniguns altogether and one of the 40mm Bofors and instead went to the configuration of two 20mm M61 Vulcan, one 40mm L/60 Bofors and one 105 mm (4.13 in) M102 howitzer, a configuration that lasted until the early 2000s when the AC-130Hs (the AC-130Es had had an avionics upgrade and redesignated to H models) underwent a refit and the two M61 Vulcans were removed and replaced with one General Dynamics 25 mm (0.984 in) GAU-12/U Equalizer 5-barrel rotary cannon (while still retaining the H suffix).

The improved MXU-470/As were even being proposed for lighter aircraft such as the Cessna O-2 Skymaster[32] used by Forward Air Controllers but proved too heavy and cumbersome. A fit of two MXU-470/As was also tested on the Fairchild AU-23A Peacemaker, though the Royal Thai Air Force later elected to use another configuration with the M197 20 mm cannon.[33]

In September 2013, Dillon Aero released the DGP2300 gun pod for the M134D-H. It contains 3,000 rounds, enough ammunition to fire the minigun for a full minute. The system is entirely self-contained, so it can be mounted on any aircraft that can handle the weight, rotational torque, and recoil force (190 lbf (850 N)) of the gun. The pod has its own battery which can be wired into the aircraft's electrical system to maintain a charge.[34]

MXU-470/A modules in an AC-47

Douglas AC-47 Spooky with SUU-11/A pods

Various iterations of the minigun have also been used in a number of armament subsystems for helicopters, with most of these subsystems being created by the United States. The first systems utilized the weapon in a forward firing role for a variety of helicopters, some of the most prominent examples being the M21 armament subsystem for the UH-1 and the M27 for the OH-6. It also formed the primary turret-mounted armament for a number of members of the Bell AH-1 Cobra family. The weapon was also used as a pintle-mounted door gun on a wide variety of transport helicopters, a role it continues to fulfill today.