The F-16C 'Falcon' has an internal 20mm M61A1 Vulcan cannon and 11 locations for mounting weapons and other mission equipment. The M61 Vulcan is a hydraulically or pneumatically driven, six-barrel, air-cooled, electrically fired Gatling-style rotary cannon which fires 20 mm rounds at an extremely high rate (typically 6,000 rounds per minute). Early F-16 had four cannon vents, while later aircraft had two.[Wiki]