In June 1946, the General Electric Company was awarded the contract for "Project Vulcan". In 1956 the T171 20mm gun was standardized by the U.S. Army and U.S. Air Force as the M61 20mm Vulcan aircraft gun.
The M61 20mm Vulcan is an externally powered, six-barrel, rotary-fire gun having a rate of fire of up to 7,200 rounds per minute. The firing rate is selectable at 4,000 or 6,000 rounds per minute. The gun fires standard electrically primed 20mm ammunition.
Each of the gun's six barrels fires only once during each revolution of the barrel cluster. The six rotating barrels contribute to long weapon life by minimizing barrel erosion and heat generation. The gun's rate of fire, essentially 100 rounds per second, gives the pilot a shot density that will enable a "kill" when fired in one-second bursts.
The M61 20mm cannon is a proven gun, having been the US military's close-in weapon of choice dating back to the 1950s. The F-104, F-105, later models of the F-106, F-111, F-4, B-47, B-52 (until the 1990's), B-58, all used the M61, as does the Air Force's F-15 , F-16 and F-22, and the Navy's F-14 and F/A-18. The primary use of the cannon is in the extremely short range (less than 2,000 feet) air-to-air environment, where more sophisticated air-to-air missiles are ineffective. Alternately, the cannon has limited usefulness in a ground strafing role.
While originally manufactured by General Electric, it is no longer produced by them; GE Armament Systems was sold to Martin Marietta; after their merger with Lockheed, it was produced by Lockheed Martin Armament Systems, which was bought by General Dynamics in 1997.
The M61 Vulcan Cannons used in the film industry have been converted to percussion primer cases using a sub caliber cartridge adapter.
This is a powered mounting used mostly by naval vessels to engage incoming missiles, aircraft, and sea-based close-range targets. It features a distinctive white-painted cylindrical weapon control group with a domed radome at the top which results in the nickname "R2-D2" being applied to the mounting; the cylinder houses the system's tracking radar, while the dome houses the search radar. More recently a land-based version called Counter-Rocket, Artillery, Mortar [C-RAM] has been developed, and is used to protect point bases against rocket attacks. Rather than using the tungsten armour-piercing discarding sabot rounds of the naval version, the land-based version uses High-Explosive Incendiary Tracer, Self-Destruct [HEIT-SD] ammunition, which was originally designed for the M163 VADS self-propelled anti-air system.
