Staff Writer (Updated: 8/22/2015):
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.