The P-51 was originally produced by North American Aviation to a request from the British Ministry of Aviation to boost RAF fighter strength. Featuing an very aerodynamically advanced laminer flow wing the airframe design was excellent, however the Allison engine lacked a supercharger, causing the aircraft to loose power and performance at higher altitutes. Changing the engine to a Packard built version of Rolls-Royce Merlin transformed the aircraft. The later D version with bubble canopy for excellent all-round visibility was the USAAF (US Army Air Force, later US Air Force) primary fighter throughout the liberation of Europe and is recognised as one of the best fighter aircraft of WW2.