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 aircraft being destroyed in accidents during testing.[1] The XF-104s were forerunners of over 2,500 production Lockheed F-104 Starfighters.