The P-51D Mustang is seen by many as one of the most iconic fighter aircraft of WWII. Clearing the German skies of Luftwaffe fighters, the P-51D was designed and built by North American Aviation as commissioned by the Royal Air Force in the 1940s. Earlier variations were initially fitted with Allison V-1710-39 engine, but by late 1943, it was re-equipped with a Rolls-Royce Merlin V-1650 engine. The P-51D variant of the Mustang also got a new bubble canopy and an increased firepower of six .50 Cal (12.7 mm) machine guns at that time. It served as a fighter, fighter-bomber and a reconnaissance plane during the war.