Curtiss P-40 Kittyhawk

During 1938 the tenth Curtiss P-36A Hawk was used for an experimental engine conversion from a radial to an inline engine, designed by Donovan Berlin and called the Model 81. Powered by the 1,150-hp Allison V-1710-9 engine and now known as the XP-40, the 14th October 1938 saw the prototype make its first flight, the pilot was Edward Elliott. Similar to the P-36A, one of the main differences would be the radiator. Initially located beneath the aft fuselage, after the prototype had flown it would be moved to under the nose. The following year on the 26th April 1939, and at the time representing the United States Army's largest single order for fighters, 524 P-40s were ordered.

The first production P-40, also known as Tomahawk Mk I, made its maiden flight on the 4th April 1940 and this along with the next two production examples were sent for service trials. Powered by the 1,040-hp Allison V-1710-33 engine, the aircraft had a top speed of 357 mph, range of 950 miles with a service ceiling of 32,750 ft. Armament consisted of two 0.50-in and two 0.30-in machine-guns. The P-40 began to enter service in June 1940 with the 33rd, 35th, and 36th Pursuit Squadrons receiving the first deliveries and by September 1940 the United States Army Air Corps had received 200 examples.

France had placed an order for 140 P-40s, but none of these arrived before the end of the Battle of France (10th May 1940 - 25th June 1940). Instead, designated Tomahawk Mk I, the aircraft were used by the Royal Air Force in Europe, where the aircraft was to prove unsuited for deployment, and after replacing Westland Lysanders of No. 2 Squadron, during August 1941, they were soon relegated to training duties. They also served in North West Africa, No. 112 Squadron was the first RAF overseas squadron to take delivery of the aircraft, and it was this squadron who would introduce the famous shark tooth design onto the aircraft. Operating in the Western Desert, in a low-level ground attack role, the P-40 enjoyed limited success.

The next production version was the P-40B, also called the Tomahawk Mk IIA, with a number of modifications adding to the weight of the aircraft, such as armour and two more 0.30-in machine-guns, and as such performance of the aircraft was reduced. Powered by the 1,090-hp Allison V-1710-33 engine, top speed was 351 mph, range 606 miles with a service ceiling of 30,000 ft. Armament was two 0.50-in and four 0.30-in machine-guns. P-40Bs would be in action with the United States Army Air Force when Japan attacked Pearl Harbor on the 7th December 1941, which brought the United States into the Second World War (1939 – 1945).

A number of P-40Bs destined for use with the Royal Air Force were instead diverted to China to serve with Brigadier General Claire Chennault's 1st American Volunteer Group, otherwise known as 'The Flying Tigers'. This squadron was working within the Chinese Air Force, playing a role in defending China from Japanese air attacks, and undertook their first operation on the 20th November 1941.

The P-40C was the next variant, also known as the Tomahawk Mk IIB. This was powered by the same engine as the P-40B, its top speed was 345 mph, range 730 miles with a service ceiling of 29,500 ft. Armament was two 0.50-in and four 0.30-in machine-guns.

The P-40D, also called the Kittyhawk Mk I, first flew on the 22nd May 1941. The product of Curtiss's redesign of the P-40C, a 1,150-hp Allison V-1710-39 engine was installed and armour was added. Other changes would also include the option of an external fuel tank. The top speed of the aircraft was 362 mph, range 650 miles with a service ceiling of 30,000 ft. Armament was four 0.50-in machine-guns. A small number of these would be built with two more 0.50-in machine-guns added, to bring the total to six, and a new designation of P-40E or Kittyhawk Mk IA given. Powered by the same engine as the P-40D, its top speed, range and service ceiling were identical. The Royal Air Force would use the Kittyhawk in North Africa, and working alongside the Hawker Hurricane, would find success in the ground attack role. A number were also converted to two-seater trainers.

As the attempts to improve the P-40 had still left its performance at altitude inadequate for it to fill the role of an effective fighter aircraft, a P-40D was used as the test bed to see if the introduction of a Rolls-Royce Merlin 28 engine could improve the situation. Flown on the 30th June 1941 the XP-40D showed improvement at high altitude and the 1,240-hp Packard Merlin V-1650-1 would power the P-40F, also called the Kittyhawk Mk II. The aircraft's top speed was 370 mph, range 752 miles with a service ceiling of 32,000 ft. Armament was six 0.50-in machine-guns and a 500lb bomb. Although the introduction of the Packard built Merlin had improved performance there was a shortage of these engines in the United States, so the P-40J had a turbocharged Allison engine to overcome this problem, however this project was abandoned in May 1942.

The P-40K would be the next variant, also known as the Kittyhawk Mk III. Powered by the 1,150-hp Allison V-1710-73 engine, it had a top speed of 363 mph, range of 700 miles with a service ceiling of 28,500 ft. Armament was six 0.50-in machine-guns. Later production P-40Ks would have a dorsal fin fitted to help fix the problem of the aircraft swinging on take-off, due to the more powerful engine.

The P-40L, also called the Kittyhawk Mk II, was another attempt by Curtiss to give the P-40 the extra performance needed to become more suited to the fighter role. Powered by the same 1,240-hp Packard Merlin V-1650-1 engine as the P-40F, and despite a weight loss of 250lb, hardly any performance increase was achieved. Its top speed was 371 mph, range 650 miles with a service ceiling of 38,550 ft. Armament comprised four 0.50-in machine-guns.

The P-40M, also known as the Kittyhawk Mk III, was powered by the 1,200-hp Allison V-1710-18 engine, which gave it a top speed of 363 mph, range of 700 miles and a service ceiling of 29,640 ft. Armament was six 0.50-in machine-guns.

As 1943 drew to a close it was clear that despite all the attempts to increase the performance of the P-40 that the aircraft's days were numbered, unless a performance increase was found. The P-40N, also called the Kittyhawk Mk IV, was the last production version, featuring a reduction in armament to four 0.50-in machine-guns, mounted in the wings, less fuel capacity and other minor changes. Powered by the 1,700-hp Allison V-1719-81 engine, top speed was 378 mph, range 750 miles and a service ceiling of 33,000 ft. Later on some P-40Ns were modified to become fighter-bombers with two more machine-guns and a bomb load of 1,500lb. The P-40N would be the most produced variant of the type.

Further efforts to improve the P-40 saw two P-40Ks and a P-40N modified to become XP-40Q prototypes. Powered by the 1,425-hp Allison V-1710-121 engine, its top speed was 422 mph.

As well as serving with the United States Army Air Force, the P-40 would serve with a number of air forces, including the Royal Air Force, who would equip 18 squadrons with the type, the Royal Canadian Air Force, four squadrons and the Royal Australian Air Force, two squadrons.

By the time production ended, on the 30th November 1944, 13,738 had been built.