The North American P-51 Mustang was designed for the RAF early in WW2. It entered combat service in 1942 and proved to be good at low altitude but lacking above 15,000 feet. The RAF's Fighter Development Unit fitted some Mustangs with Rolls Royce Merlin engines and it proved to be a stroke of genius - The Mustang was now faster than almost anything and could reach over 40,000 feet altitude. The USAF became interested, and North American began producing Mustangs with a Packard Merlin engine as a new fighter to escort bombers on long-range missions.
There were several modifications, and the final 'D' versions had a 'bubble' canopy for better visibility. The Mustang was armed with 6 x 12.7mm machine guns, and was also adapted for ground-attack with rockets and bombs being carried in the Korean War and later in Central America.
The P-51 was known as the F-51 when it was exported in large numbers and the end of WW2. The Mustang was used extensively well after then, by many air forces, with some being on active service until 1984!
This example is a P-51D of the 78th Fighter Squadron, circa 1945.