North American P-51 Mustang

In 1940 North American Aviation President James J. Kindelberger 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 need for fighter aircraft and the Curtiss P-40 Kittyhawk the only aircraft close to the specification required, but only available in limited numbers, North American Aviation was asked, under licence from Curtiss-Wright, to produce the P-40. North American Aviation felt 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.

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. On the 9th September 1940, just 102 days later, the prototype airframe, designated NA-73X, was completed, minus its 1,100-hp Allison V-1710-39 engine which was running behind schedule. On the 26th October 1940 the prototype made its maiden flight and the first production aircraft flew on the 23rd April 1941.

It would be with the Royal Air Force that the aircraft, known as the Mustang Mk I, would begin its operational career. Powered by the 1,150-hp Allison V-1710-39 engine, at higher altitude the performance of the aircraft suffered as its Allison engine power output fell rapidly as it climbed, its top speed was 382 mph, range 1,000 miles with a service ceiling of 31,350 ft. Armament was four 0.50-in machine-guns and four 0.30-in machine-guns. It would be No. 26 Squadron based at RAF Gatwick, who were part of Army Co-operation Command, who received the first Mustang Mk Is on the 5th January 1942 to replace their Curtiss P-40s. They would fly their first operation on the 5th May 1942. 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. 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.

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 they had already ordered 150 more aircraft, with some to be sent to Britain under Lend-Lease. These aircraft, also known as the Mustang Mk IA, featured self-sealing fuel tanks and were powered by the 1,150-hp Allison V-1710-39 engine. This gave the aircraft a top speed of 390 mph, a range of 1,050 miles and a service ceiling of 32,000 ft. Armament consisted of four 0.50-in machine-guns.

The A-36 was the first P-51 variant to go into operational service with the United States Army Air Force. These were modified P-51s fitted with dive brakes and bomb racks to provide close support to ground troops and 500 were ordered on the 21st August 1942. Powered by the 1,325-hp Allison V-1710-87 engine, its top speed was 365 mph, range 550 miles with a service ceiling of 25,250 ft. Armament was six 0.50-in machine-guns and 1,000lb bombs. The first A-36 flew on the 21st September 1942, equipping two groups based in the Middle East during 1943.

The P-51A followed, also known as the Mustang Mk II, powered by the 1,200-hp Allison V-1710-81 engine. This gave the aircraft a top speed of 390 mph, a range of 1,050 miles and a service ceiling of 31,350 ft. Armament consisted of four 0.50-in machine-guns and 1,000lb bombs.

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 Rolls-Royce Merlin 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 Packard Merlin V-1650-3 engine was installed into two P-51s, initially designated XP-78 but later XP-51B. The XP-51B made its maiden flight on the 30th November 1942, achieving a top speed of 441 mph. With its impressive performance backing the tests performed by the British, the United States Army Air Force placed large orders for the Merlin powered P-51.

The P-51B and P-51C would be the first Merlin powered variants and featured a number of small changes to accommodate the new engine. Both these variants were the same, the only difference being where they were built. P-51Bs were built at Inglewood and P-51Cs at Dallas. Powered by either the 1,620-hp Packard Merlin V-1650-3 or the 1,695-hp Packard Merlin V-1650-7 engine, their top speed was 439 mph, range 1,180 miles with a service ceiling of 41,800 ft. Armament was four 0.50-in machine-guns and either 2,000lb bombs or rocket projectiles. The P-51B was the first to enter operational service with the United States Army Air Force in Britain, as part of the Eighth Air Force. The 13th December 1943 saw the P-51B 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 external fuel tanks, would provide escort for bombers of the Eighth Air Force during daylight operations deep into the heart of Germany. The Tenth Air Force and Fifteenth Air Force in Burma and Italy respectively would also be equipped with the P-51B and P-51C.

The Royal Air Force started to receive their Lend-Lease P-51B and P-51Cs, designated Mustang Mk III, in January 1944 when No. 19 Squadron based at RAF Gravesend were the first to receive the type, replacing their Supermarine Spitfire Mk IXs. 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.

The next production version was the P-51D, with a modified rear fuselage and a bubble canopy, and powered by the 1,695-hp Packard Merlin V-1650-7 engine. This gave the aircraft a top speed of 437 mph, a range of 1,180 miles and a service ceiling of 41,900 ft. Armament consisted of six 0.50-in machine-guns and either 2,000lb bombs or 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 produced and a new low drag section of wing replaced the laminar-flow design and the oil cooler was replaced with a heat exchanger. With a simpler structure and the removal of equipment no longer deemed necessary and using new lightweight materials, a significant reduction in the aircraft's weight was achieved. The XP-51F, which made its maiden flight on the 14th February 1944, and the XP-51G, which flew for the first time on the 9th August 1944 were followed by two XP-51J prototypes of a similar design, however, only one was finished and this would be powered by a 1,500-hp Allison V-1710-119 engine.

The P-51H was the next variant and the last to go into production, with the prototype flying for the first time on the 3rd February 1945. Powered by the 1,900-hp Packard Merlin V-1650-9 engine, its top speed was 437 mph, range 1,180 miles with a service ceiling of 41,780 ft. Armament was six 0.50-in machine-guns and either 2,000lb bombs or rocket projectiles.

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).

The P-51 also saw service with China, the Netherlands and the American Volunteer Group. 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. The last P-51 was retired from the Dominican Air Force in 1984.

In total 15,576 P-51s were built by the time production ended