Perhaps one of the most popular aircraft designs to emerge from World War II, the North American Aviation P-51 Mustang design and development was due to close work between the British government and American engineers. The first Mustangs entered service with the Royal Air Force in January 1942. The U.S. took a little time to warm up to the Mustang, but by November 1942 had ordered for 400 aircraft. They would begin service in the winter of 1943-44, soon moving to the P-51B with a bigger Merlin engine and additional fuel tank that provided the range and high-altitude performance to escort long-range bombers. Five Canadian squadrons were equipped with Mustangs during WWII, including P-51Bs, Cs, and Ds, called Mk. II, Mk.III, and Mk.IV respectively. This P-51D was initially a USAAF aircraft before being repainted as a Royal Canadian Air Force Mk.IV bird.