M61 Vulcan - Development

Development

At the end of World War II, the United States Army began to consider new directions for future military aircraft guns. The higher speeds of jet-engined fighter aircraft meant that achieving an effective number of hits would be extremely difficult without a much higher volume of fire. While captured German designs (principally the Mauser MG 213C) showed the potential of the single-barrel revolver cannon, the practical rate of fire of such a design was still limited by ammunition feed and barrel wear concerns. The Army wanted something better, combining extremely high rate of fire with exceptional reliability.

In response to this requirement, the Armament Division of General Electric resurrected an old idea: the multi-barrel Gatling gun. The original Gatling gun had fallen out of favor because of the need for an external power source to rotate the barrel assembly, but the new generation of turbojet-powered fighters offered sufficient electric power to operate the gun, and electric operation offered reliability superior to a gas operated weapon.

With multiple barrels, the rate of fire per barrel could be lower than a single-barrel revolver cannon while still giving a superior total rate of fire. The idea of powering a Gatling gun from an external electric power source was not a novel idea at the end of the World War II era, as Richard Jordan Gatling himself did just that in a patent he filed in 1893.

The Army issued General Electric the contract in 1946 for "Project Vulcan", a six-barrel weapon capable of firing 7,200 rounds per minute (rpm). Although European designers were moving towards heavier 30 mm weapons for better hitting power, the U.S. initially concentrated on a powerful .60 caliber (15 mm) cartridge designed for a pre-war anti-tank rifle, expecting that the cartridge's high muzzle velocity would be beneficial for improving hit ratios on high speed targets.

The first GE prototypes of the .60 caliber T45 were ground-fired in 1949; it achieved 2,500 rpm, which was increased to 4,000 rpm by 1950. By the early 1950s, the USAF decided that high velocity alone might not be sufficient to ensure target destruction and tested 20 mm and 27 mm alternatives based on the .60 caliber cartridge. These variants of the T45 were known as the T171 and T150 respectively, and were first tested in 1952. Eventually, the 20 x 102 mm cartridge was determined to have the desired balance of projectile and explosive weight and muzzle velocity.

The development of the Lockheed F-104 Starfighter revealed that the T171 Vulcan (later redesignated M61) suffered problems with its linked ammunition, being prone to misfeed and presenting a foreign object damage (FOD) hazard with discarded links. A linkless ammunition feed system was developed for the upgraded M61A1, which subsequently became the standard cannon armament of U.S. fighters.

In 1993, General Electric sold its aerospace division, including GE Armament Systems along with the design and production tooling for the M61 and GE's other rotary cannon, to Martin Marietta. After Martin's merger with Lockheed, the rotary cannon became the responsibility of Lockheed Martin Armament Systems. Lockheed Martin Armament Systems was later acquired by General Dynamics, who currently produce the M61 and its various offspring.