- The P-51 Mustang was developed by North American Aviation under contract to the British Air Purchasing Commission prior to the United States' entry into World War II. The original request by the BAPC was intended for an order of the then-established P-40 Warhawk fighters to be built, but James H. Kendelberger, president of North American, convinced the British that he could develop a more advanced fighter, despite his company's only prior fighter building experience having been limited production of a light fighter designed for export sale.
- The P-51 Mustang was designed and built in 120 days, according to contractual terms set forth by the British Air Purchasing Commission. The first plane to be built had no engine, and its builders used parts from other planes to produce a complete aircraft. This was done in order to fulfill the North American company's contract with BAPC on time. The plane did not actually fly until several weeks after its first rollout from the production line.
- Upon initial flight tests, the P-51 outperformed the P-40 it was intended to replace as well as other top-level aircraft of the time. It was quickly recognized as an exceptional aircraft, and the British Air Purchasing Commission quickly approved and placed orders for over 300 of the planes.
The original P-51 Mustang was built with a 1,100 hp Allison V-1710-39 engine that was currently used in the P-40 fighter. The P-51 design incorporated an advanced and unique laminar flow wing design that reduced drag and increased range, allowing the P-51 to surpass the top speed of the P-40 by 25 mph with the same engine. This engine gave the plane a top speed of 382 mph but limited the P-51 to flying under 15,000 feet because of its inability to operate in the thinner air of higher altitudes. Because of this, the P-51 first saw use in the RAF as an armed tactical reconnaissance aircraft for low altitude missions.
- The P-51 was fitted with the Rolls-Royce Merlin engine in 1943 which increased the available horsepower to 1,695, and increased the aircraft's top speed by 51 mph to 441 mph. More importantly, this engine greatly increased the altitude as which the plane could operate from 15,000 feet to 40,000 feet in testing. This change in engines made the P-51 the fastest and longest range fighter of WWII. Further improvements were made throughout the Mustang's production run, and the plane eventually was capable of reaching over 480 mph, making it arguably the fastest mass-produced piston engine plane of World War II.
- The P-51's armament varied, with the most common configurations carrying six .50-caliber machine guns in the wings, 10 under-wing rockets, and carrying capacity for 1,000 pounds of bombs or external fuel tanks to increase range.
- The P-51 Mustang is considered one of the best fighter aircraft of World War II and eventually was used in all aspects of aerial combat operations. The Mustang was produced in large numbers, with U.S. production totaling 15,386 aircraft. Much smaller numbers of the P-51 were produced by other countries, with Australia producing 200.
- The P-51 saw combat in two wars, World War II and the Korean War. It was credited with the most kills of any American fighter in the war over Europe and the first fighter kills in the Korean War. The P-51 earned several honors and awards, and was declared "the most aerodynamically perfect pursuit plane in existence" by the Truman Senate War Investigating Committee. It has been used by over 55 countries and has one of the longest service histories of any fighter aircraft. P-51s today are a favorite among racers and collectors and are commonly present at airshows. Their value has skyrocketed, with restored planes as of 2010 being sold for three quarters of a million dollars or more.