The P-51 made a low key start to it's operational service but after the installation of the Rolls-Royce Merlin engine the North American P-51 Mustang ended the Second World War as
one of, if not, the best Allied fighter, and stayed in service with the United States into the 1950s.
The story of the North American Aviation (NAA) P-51 Mustang began in 1940 when NAA President James J. Kindelberger had approached the British Purchasing Commission to sell NAA's twin
engined bomber the B-25 Mitchell. However with the Royal Air Force (RAF) in desperate need for fighter aircraft and the Curtiss P-40 Kittyhawk being the only plane coming close to the
specification required for the air war in Europe and even this aircraft was only available in limited numbers. So NAA was asked, under licence from Curtiss-Wright, to produce the P-40.
NAA felt, however, that they could have a better aircraft working quicker than it would take a production line to produce the P-40 to be set up. Whilst it was agreed for NAA to supply this
new aircraft instead it was required for a prototype to be ready in 120 days.
Although this looked like a tall order NAA already had a design outline for a plane which benefited from information from the air war in Europe. Under the leadership of Raymond Rice and
Edgar Schmued the design team set about fitting the new fighters design to the specification laid out by the British. And impressively just 117 days later the prototype airframe designated
NA-73X was completed, however due to the 1,100-hp Allison V-1710-39 engine, which was to power the plane, running behind schedule, it wasn't until a couple of months later on the 26th October 1940
when the prototype finally flew for the first time.
In a little under seven months and after a very successful testing programme the first production aircraft flew on the 1st May 1941 and six months later the RAF received the second
production NA-73 for evaluation. The NA-73 as with a number of other aircraft used by the British, such as the Hawker Tempest and Fairey Battle, an order had been placed before the
prototype had even flown and so more of the aircraft soon followed.
Designated Mustang I by the RAF, initial evaluation showed that at low-level the plane was fast and extremely manoeuvrable and was much better than any other US fighter then available.
At higher altitude the performance of the plane suffered as its Allison engine power output fell rapidly as it climbed, meaning that despite the Mustang's promise it wasn't suitable for
a combat role in Europe.
With its eight machine-guns comprising four 0.50-in and four 0.303-in and it's superb performance at low-level it was within this role that the Mustang would serve with No.2 Squadron of Army
Co-operation Command during April 1942, equipped with obliquely-mounted cameras and on on the 27th July they flew their first operational sortie. Just three months later however and the
Mustang showed its potential for long range escort duties when in October 1942 on an attack on the Dortmund-Ems canal it became the first RAF single-engined fighter to cross the German
border from its base in Britain, however the performance of the aircraft at higher altitude still needed to be improved, but an order for another 300 aircraft was placed.
One of the conditions to allow North American to supply the RAF with it's NA-73 design was that two aircraft were given to the United States Army Air Corps (USAAC) for evaluation under the
designation XP-51. Before these two aircraft were supplied to the USAAC the US Army had already ordered 150 more aircraft to be sent to Britain under the lend-lease programme.
These planes featured self-sealing tanks and instead of eight machine-guns featured four 20-mm cannons and were designated P-51 by the US and Mustang IA by the British.
A number of these planes went to the United States Army Air Force (USAAF) designated F-6A and were used for tactical reconnaissance and were fitted with two K-24 cameras. And two examples
initially designated XP-78 but later XP-51B were each tested with different engines and th