The North American P51 Mustang was one of, if not considered the best, fighter the Allies created during WWII. First powered by the Allison engine it's airframe proved capable but the engine lacked the power necessary for high altitudes. In came the Merlin engine, produced by Rolls Royce. Once mated with the Mustang airframe, created a devil of a machine in a fight. But was considered the 'Cadillac of the Skies'.