M39 cannon
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The M39 cannon is a 20 mm caliber single-barreled revolver cannon developed for the United States Air Force in the late 1940s. It was used on a number of fighter aircraft from the early 1950s through the 1980s. Wikipedia
Designer: Ford Motor Company
Action: five-chamber revolver
Barrels: Single barrel (progressive RH parabolic twist, 9 grooves)
Caliber: 20 mm (0.8 in)
Cartridge: 20×102mm
In service: 1952–present
Length: 1.83 m