After World War II, the U.S. Army Air Force determined that an improved automatic cannon with an extremely high rate of fire was required against fast-moving enemy jet aircraft. Using experience gained from the Luftwaffe MG 151 and MK 108 cannons, a larger-caliber cannon shell for the new gun was deemed desirable. In June 1946, the General Electric Company was awarded a U.S. military defense contract to develop a high-ROF aircraft gun, which GE termed "Project Vulcan". While researching prior work, ordnance engineers recalled the experimental electrically-driven Gatling weapons from the turn of the 20th century. In 1946, a Model 1903 Gatling gun borrowed from a museum was set up with an electric motor and test-fired, briefly managing a rate of 5,000 rounds per minute. In 1949, GE began testing the first model of its modified Gatling design, now called the Vulcan Gun. The first prototype was designated the T45 (Model A), firing ammunition at about 2,500 rounds per minute from six barrels, and in 1950 GE delivered ten initial Model A .60 cal. T45 guns for evaluation. Thirty-three model C T45 guns in three calibers (.60 cal., 20 mm and 27 mm) were delivered in 1952 for additional testing. After extensive testing, the T171 20mm gun was selected for further development, and was standardized by the U.S. Army and U.S. Air Force in 1956 as the M61 Vulcan gun.
