It was a rush order, but North American designers finished the XP-51 prototype in just 117 days. What’s more amazing is that it became one of the best fighters of World War II. The XP-51 prototype reached 382 mph, exceeding the Curtiss P-40's top speed by 25 mph and it even outperformed the Spitfire. When it was finally matched with the British Rolls Royce Merlin engine, the level airspeed increased to 441 mph making it the fastest piston-engine fighter of World War II. 14,819 Mustangs of all types were built and they destroyed 4,950 enemy aircraft in Europe to make them the highest scoring USAAF fighter. Read More ...