High Quality Content by WIKIPEDIA articles! The Lockheed XF-104 was a single-engine, high-performance, supersonic interceptor prototype for a United States Air Force (USAF) series of lightweight and simple fighters. Only two aircraft were built, one aircraft was used primarily for aerodynamic research and the other served as an armament testbed. Both prototypes were destroyed in accidents during testing. The XF-104 was the forerunner of over 2,500 Lockheed F-104 Starfighters.