The Mustang was designed in by a team headed by James H. Rather than build an old design from another company, NAA proposed the design and production of a more modern fighter. The prototype NAX airframe was completed on 9 September , days after contract signing, achieving its first flight on 26 October.
The Mustang was designed to use the Allison V engine without an export-sensitive turbosupercharger [ 6 ] or a multi-stage supercharger, resulting in limited high-altitude performance. The aircraft was first flown operationally and very successfully by the RAF and as a tactical-reconnaissance aircraft and fighter-bomber Mustang Mk I.
In mid , a development project known as the Rolls-Royce Mustang X , replaced the Allison engine with a Rolls-Royce Merlin 65 two-stage inter-cooled supercharged engine.
During testing at Rolls-Royce's airfield at Hucknall in England , it was clear the engine dramatically improved the aircraft's performance at altitudes above 15, ft 4, m without sacrificing range. At the start of the Korean War, the Mustang, by then redesignated F , was the main fighter of the United States until jet fighters , including North American's F Sabre , took over this role; the Mustang then became a specialized fighter-bomber.
Despite the advent of jet fighters, the Mustang remained in service with some air forces until the early s. After the Korean War, Mustangs became popular civilian warbirds and air racing aircraft.
