The P-51D was arguably the definitive variant of the North American Mustang and included several significant improvements to the aircraft’s already successful design. These included a new bubble canopy for greater pilot visibility, the introduction of an effective new K-14 gunsight, even greater firepower, improvements to the ammunition feed system to reduce jamming and the availability of lightweight external fuel tanks, to further extend the fighter's range.
 
The Mustang made a significant contribution to the eventual Allied victory in Europe, destroying more enemy aircraft in air-to-air combat than any other USAAF fighter in the European Theatre.