The General Electric GAU-17/A "minigun" represents the USAF/USN derivative of the U.S. Army's Vietnam War-era General Electric M134 Minigun vehicler-mounted weapon system. The GAU-17 operation follows the Gatling rotary-style munitions delivery arrangement pioneered by Dr. Richard J. Gatling during the 1880's. These early forms relied on a hand-cranked mechanical action to rotate their barrels and feeding was by way of top-inserted cartridges. The concept proved sound and was revisited quite some time later when an electric motor was installed to supply power for the needed rotary action. Despite its 1960s origins, the GAU-17/A is a standardized suppression weapon still in use today (2015)) by conventional and special forces elements.
The original General Electric Gatling gun attempt was developed under the project name of "Vulcan". The program produced the M61 Gatling system, and aircraft-mounted rotary cannon firing 20mm projectiles. With the increasing use of helicopters as armed assault ships (gunships) during the Vietnam War, the M61 was reworked by General Electric to a more compact form, becoming relatively portable M134 Minigun series chambered to fire the NATO-standard 7.62x51mm rifle cartridge at an impressive 6,000 rounds-per-minute. The M134 was a prominent fixture on U.S. Army helicopters and fixed-wing gunships throughout the Vietnam War when it was found that slow, low-flying aircraft prove susceptible to ground fire originating from the cover of the jungle. A suppression weapon was needed to clear jungle and assail the enemy hiding beneath.
The GAU-17/A, although essentially similar in most respects to the U.S. Army's M134. It features a firing selector switch for "low rate" firing at 2,000 rounds-per-minute or "high rate" firing at 4,000 rounds-per-minute (the Army's originally fired at a fixed 6,000 rounds-per-minute). The GAU-17/A fires the same 7.62x51mm cartridge as the Army M134. Ammunition "cook-off" is avoided by having a deliberate delay installed in the firing action and this is activated after the trigger is released to ensure all six barrels are cleared of loaded cartridges before coming to a complete stop. Full magazines can be issued in various counts ranging from 1,500 rounds to 4,400 rounds as needed.
Broken down into its core components, the GAU-17/A system consists of the six-barrel rotary M134D gun system, the electrically-powered drive motor, a de-linking ammunition feeder, the ammunition canister, a flexible ammunition feed and the electrical gun control assembly with associated cabling for the power supply. The barrels are fitted with a flash suppressor made of titanium and the barrel unit rotates counterclockwise when viewing the weapon from behind the trigger.
GAU-17/A Miniguns are still highly-prized suppression weapons in the American military and have seen widespread acceptance in the inventories of American allies the world over. The USAF/USN services use the designations GAU-2/A and GAU-17A denoting their fixed and flexible mounts respectively. The USMC also uses the GAU-17A.