The United States didn’t enter the war until 1941, after the December 7th attack on Pearl Harbor by the Japanese Navy. The Mustang was first built out of a request by RAF pilots who were outmatched in the outdated Curtiss P-40 Warhawk. In 1940, less than three months after the idea was first brought up, the first ever Mustangs were produced by North American, a company that is now defunct but was formerly part of Boeing. The first run of Mustangs, powered by an Allison V12 was a huge improvement over the P-40, but not quite the Mustang everyone knows today.
Around two years later, RAF engineers decided to equip a Mustang with a supercharged V12 made by Rolls-Royce and designated the “Merlin” after the famed wizard of Arthurian legend. Packard, the car company, produced the engine from Rolls-Royce’s design for combat ready versions of the aircraft. And the Merlin worked its magic as the P-51B, C, and later D were able to reach a top speed of 437 miles per hour, had a maximum ceiling of 41,900 feet, and a range of 1,000 miles. Those factors, combined with incredible maneuverability made the Mustang the absolute cutting edge of Allied aircraft and would prove to be the bane of many Nazi and Imperial Japanese aircraft.
