The North American F-86 Sabre was a subsonic combat aircraft developed for the US Air Force. The F-86 was developed in the 1940s following the end of WWII and was one of the most-produced western jet fighters. Initial proposals to meet a USAAF requirement for a single-seat high-altitude day fighter aircraft/escort fighter/fighter bomber were made in late 1944, and were derived from the design of the straight-wing FJ Fury being developed for the US Navy. Performance requirements were met by incorporating a swept-back wing with a 5:1 aspect ratio into the design. Manufacture was not begun until after World War II as a result. The XP-86 prototype, which would become the F-86 Sabre, first flew on October 1, 1947. The F-86 was manufactured as both a fighter-interceptor and fighter-bomber. Several variants were introduced over its production life, with improvements and different armaments implemented (see below). As an example, the J47-GE-7 engine of the F-86A produced a thrust of only 5,200 lbf (23 kN) while the J47-27 engine of the F-86F produced 10,000 lbf (44 kN) of thrust. F-86s were the primary US air-combat fighter during the Korean War, with significant numbers of the first three production models seeing combat.