North American P-51 Mustang

The story of the P-51 began in 1940 when North American Aviation President James J. Kindelberger had approached the British Purchasing Commission to sell North American Aviation's twin engined bomber, the B-25 Mitchell. However with the Royal Air Force in desperate need for fighter aircraft and the Curtiss P-40 Kittyhawk being the only aircraft coming close to the specification required for the air war in Europe and even this aircraft was only available in limited numbers. So North American Aviation was asked, under licence from Curtiss-Wright, to produce the P-40. North American Aviation 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 North American Aviation 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, North American Aviation already had a design outline for an aircraft 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 102 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 aircraft, 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 Royal Air Force received the second production NA-73 for evaluation. The NA-73 had been ordered before the prototype had even flown and so more of the aircraft soon followed. Designated Mustang Mk I by the RAF, initial evaluation showed that at low-level the aircraft was fast and extremely manoeuvrable and was much better than any other American fighter then available. At higher altitude the performance of the aircraft suffered as its Allison engine power output fell rapidly as it climbed.

With eight machine-guns comprising four 0.50-in and four 0.30-in and its superb performance at low level it would be an ideal replacement for No. 26 Squadron's Curtiss P-40 Tomahawks that they were using. They began to receive their first Mustang Mk Is on the 5th January 1942 and would fly their first operation on the 5th May 1942. Other use of the aircraft saw it equip No. 2 Squadron of Army Co-Operation Command during April 1942, equipped with obliquely-mounted cameras, and on the 27th July 1942 they flew their first operational sortie. Its first aerial victory came on the 19th August 1942 during the Dieppe Raid when Flying Officer Hollis Hills of No. 414 Squadron, Royal Canadian Air Force shot down a Focke-Wulf Fw 190.

Just two months later the Mustang showed its potential for long-range escort duties when on the 22nd October 1942, on an attack on targets in Germany, it became the first Royal Air Force 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 Aviation to supply the Royal Air Force with its NA-73 design was that two aircraft were given to the United States Army Air Corps for evaluation under the designation XP-51. Before these two aircraft were supplied to the USAAC the United States Army had already ordered 150 more aircraft to be sent to Britain under Lend-Lease. These aircraft 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 Mk IA by the British.

Two examples initially designated XP-78, but later XP-51B, were each tested with different engines and they proved very successful and the Royal Air Force's findings of superb performance at low-level was confirmed. However the United States was committed to the Lockheed P-38 Lightning and Republic P-47 Thunderbolt, nevertheless 500 P-51's modified to have dive brakes and bomb racks to provide close support to ground troops and designated A-36 were ordered on the 21st August 1942. The first A-36 flew on the 21st September 1942 powered by a Allison V-17110-87 engine with six 0.50-in machine-guns, they were the first Mustang variant to go into operational service with the United States Army Air Force. Equipping two groups based in the Middle East during 1943 they also performed support operations during the invasions of Sicily and Italy. As well as ordering the A-36 an order for just over 310 P-51As had been placed by the United States with armament of four 0.50-in machine-guns and racks for either 1,000lb of bombs or two of either 75 or 150 US gallon external fuel tanks, this was designated Mustang Mk II by the RAF and powered by a 1,200-hp Allison V-1710-81 engine.

After showing its ability for potential long-range escort duties into Germany, but lacking high-altitude performance, during 1942 the decision was taken to install Rolls-Royce Merlin 61 and 65 engines in four airframes of the Mustang Mk I. Testing showed a much improved performance and North American Aviation were informed of the results and a 1,430-hp US-built Packard Merlin V-1650-3 engine was installed into two P-51s, these would be designated XP-78/XP-51B. Tested during September 1942 and achieving a maximum speed of 441 mph and having a better rate of climb than the P-38 Lighting, and confirming the British findings, the United States Army Air Force, impressed with the performance, ordered the Merlin powered Mustang in large numbers.

P-51B and P-51Cs, which featured a strengthened fuselage, improved ailerons and a number of small changes, to accommodate the new engine, and armament of four 0.50-in machine-guns, began to enter operational service with the United States Army Air Force in Britain as part of the Eighth Air Force. The 13th October 1943 saw this new aircraft complete its first long-range escort mission when a force of bombers were sent to attack the U-boat yard at Kiel, Germany. The P-51, with the benefit of external fuel tanks, would provide regular escort for bombers of the Eighth Air Force, during their perilous daylight operations deep into the heart of Germany. During March 1944 the P-51 took part in its first mission to Berlin and started being used operationally by both the 10th and 15th Air Force in Burma and Italy respectively. The Royal Air Force also started to receive their Lend-Lease P-51B/P-51Cs, designated Mustang Mk III, around the same time and No. 19 Squadron based at RAF Ford were the first to receive this new type, which would eventually be used by at least 21 RAF squadrons, many of which were part of the Second Tactical Air Force. The RAF modified the original cockpit canopy which opened sideways to a sliding hood design to overcome the poor rear view of the original canopy design.

Development of the aircraft continued and the next production version was the P-51D, with a modified rear fuselage, six 0.50-in machine-guns and a bubble canopy as standard, this was to become the most produced version of the P-51. Later versions of the P-51D had a small dorsal fin added and racks to accommodate 5-in rocket projectiles. A change in propeller led to a change in designation to P-51K, and both of these aircraft were designated Mustang Mk IV and Mustang Mk IVA respectively by the Royal Air Force.

During 1944 as part of experiments into lightweight construction the United States Army Air Force had ordered three XP-51Fs and two XP-51Gs as part of this process. A new redesigned airframe was also produced and as a result of an overview of the aircraft a new low drag section of wing replaced the laminar-flow design, the oil cooler was also replaced with a heat exchanger and the cockpit canopy was stretched to reduce drag further. With a simpler structure and the removal of equipment no longer deemed necessary and the use of new lightweight materials being used a significant reduction in the aircraft's weight was achieved. Both prototypes were powered by different engines with a 1,695-hp Packard Merlin V-1650-7 engine powering the XP-51F and a 1,140-hp Rolls-Royce Merlin 145m engine powering the XP-51G. Two P-51J prototypes of a similar design were ordered, however only one was finished and this would be powered by a Allison V-1710-119, 1,720-hp engine.

As a result of the prototypes the P-51H appeared, flying for the first time on the 3rd February 1945, powered by the V-1650-0 Packard Merlin engine, this was to be both the last production P-51 and the fastest with a top speed of 487 mph. Further improvements had been made to the aircraft and as a result the aircraft was 40% lighter than the last P-51 in wartime service, the P-51D.

Another permutation of the P-51 was the P-82 Twin Mustang which was two aircraft merged together, however this didn't see service in the Second World War (1939 – 1945).

A grand total of 15,576 P-51s were built by the time production ended, seeing service with China, Netherlands and a few were also supplied to the American Volunteer Group in China. The end of the war didn't see the end of the aircraft, as it remained in service with the United States Air Force, although under a different designation of F-51, until the 27th January 1957 when a F-51D, from the 167th Fighter Bomber Squadron, performed the types last flight with the USAF. In fact the last P-51 was retired from the Dominican Air Force in 1984.