The F-16 is a single-engine multi-role fighter aircraft originally developed by General Dynamics for the USAF. Designed as an air superiority day fighter, it has evolved into a successful all-weather multi-role aircraft with the ability to switch between an air-to-ground and an air-to-air role at the touch of a button. Over 4,600 F-16s have been built since production was approved in 1976 and combined have flown over 400k combat sorties with 19 million flight hours. 3,000 operational F-16s are in service today with the air services of 25 different countries. The F-16's official name is "Fighting Falcon", but "Viper" is commonly used by its pilots and crews, due to a perceived resemblance to a viper snake as well as the Colonial Viper on TV's Battlestar Galactica which aired at the time the F-16 entered service. The F-16 has an internal M61 Vulcan cannon and 11 locations for mounting weapons and other mission equipment.