The General Dynamics F-16 Fighting Falcon is a single-engine multirole fighter aircraft originally developed by General Dynamics (now Lockheed Martin) for the United States Air Force (USAF). Designed as an air superiority day fighter, it evolved into a successful all-weather multirole aircraft. Over 4,500 aircraft have been built since production was approved in 1976.[3] Although no longer being purchased by the U.S. Air Force, improved versions are still being built for export customers.[4] In 1993, General Dynamics sold its aircraft manufacturing business to the Lockheed Corporation,[5] which in turn became part of Lockheed Martin after a 1995 merger with Martin Marietta.