The Curtiss P-40 Warhawk is an American single-engined, single-seat, all-metal fighter-bomber that first flew in 1938. The P-40 design was a modification of the previous Curtiss P-36 Hawk which reduced development time and enabled a rapid entry into production and operational service. The Warhawk was used by most Allied powers during World War II, and remained in frontline service until the end of the war. It was the third most-produced American fighter of World War II, after the North American P-51 Mustang and Republic P-47 Thunderbolt; by November 1944, when production of the P-40 ceased, 13,738 had been built,Murphy and McNiece 2009, p. 83. all at Curtiss-Wright Corporation's main production facilities in Buffalo, New York.

The British Commonwealth from 1940 and Soviet air forces used the name Tomahawk for models equivalent to the original P-40, P-40B, and P-40C (Curtiss Model 81), and the name Kittyhawk for models equivalent to the P-40D and all later variants (Curtiss Model 87). P-40 Warhawk was the name the United States Army Air Corps gave the plane; after June 1941, the USAAF adopted the name for all models, making it the official name in the US for all P-40s. P-40s first saw combat with the British Commonwealth squadrons of the Desert Air Force in the Middle East and North African campaigns, during June 1941.Alexander 2006, p. 25.Brown 1983, p. 20. No. 112 Squadron Royal Air Force, was among the first to operate Tomahawks in North Africa and the unit was the first Allied military aviation unit to feature the "shark mouth" logo,Crawford 1977, p. 14.Vader 1970, p. 95. copying similar markings on some Luftwaffe Messerschmitt Bf 110 twin-engine fighters.

The lack of a two-speed supercharger for the P-40's Allison V-1710 engine made it inferior to Luftwaffe fighters such as the Messerschmitt Bf 109 or the Focke-Wulf Fw 190 in high-altitude combat and it was rarely used in operations in Northwest Europe. However, between 1941 and 1944, the P-40 played a critical role with Allied air forces in three major theaters: North Africa, the Southwest Pacific, and China. It also had a significant role in the Middle East, Southeast Asia, Eastern Europe, Alaska and Italy. The P-40's performance at high altitudes was not as important in those theaters, where it served as an air superiority fighter, bomber escort and fighter-bomber.

Although it gained a postwar reputation as a mediocre design, suitable only for close air support, more recent research including scrutiny of the records of Allied squadrons indicates that this was not the case; the P-40 performed surprisingly well as an air superiority fighter, at times suffering severe losses, but also inflicting a very heavy toll on enemy aircraft.Masell, Patrick. "The P-40 and the Zero". Naval Aviation and Military History, 2002. Retrieved: 7 March 2006. Based on war-time victory claims, over 200 Allied fighter pilots – from the UK, Australia, New Zealand, Canada, South Africa, the US and the Soviet Union – became aces flying the P-40. These included at least 20 double aces, mostly over North Africa, China, Burma and India, the South West Pacific and Eastern Europe.See Molesworth 2000, 2003, 2006, 2008 The P-40 offered the additional advantages of low cost and durability, which kept it in production as a ground-attack aircraft long after it was obsolescent as a fighter.

Design and development

Origins

On 14 October 1938, Curtiss test pilot Edward Elliott flew the prototype XP-40 on its first flight in Buffalo."Chronology: The Army Air Corps to World War II". Air Force Historical Studies Office. Retrieved: 20 July 2011. The XP-40 was the 10th production Curtiss P-36 Hawk,Green 1957, p. 43. with its Pratt & Whitney R-1830 Twin Wasp 14-cylinder air-cooled radial engine replaced at the direction of Chief Engineer Don R. Berlin by a liquid-cooled, supercharged Allison V-1710 V-12 engine. The first prototype placed the glycol coolant radiator in an underbelly position on the fighter, just aft of the wing's trailing edge.Merriam 2000, p. 15. USAAC Fighter Projects Officer Lieutenant Benjamin S. Kelsey flew this prototype some 300 miles in 57 minutes, approximately . Hiding his disappointment, he told reporters that future versions would likely go faster.American Aviation, Volume 3, 1939, p. 2. Kelsey was interested in the Allison engine because it was sturdy and dependable, and it had a smooth, predictable power curve. The V-12 engine offered as much power as a radial engine but had a smaller frontal area and allowed a more streamlined cowl than an aircraft with a radial engine, promising a theoretical 5% increase in top speed.Wilson, Randy. "The Heart of the Cobra: Development of the Allison V-1710 Engine". Allison Press Release on the Certification of its V-1710 Engine by the Air Corps via The Dispatch, Volume 22, Number 1, Spring, 1997. Retrieved: 20 July 2011.

Curtiss engineers worked to improve the XP-40's speed by moving the radiator forward in steps. Seeing little gain, Kelsey ordered the aircraft to be evaluated in a NACA wind tunnel to identify solutions for better aerodynamic qualities. From 28 March to 11 April 1939, the prototype was studied by NACA.Wagner, Ray. "P-40". American Combat Planes of the 20th century. Retrieved: 20 July 2011. Based on the data obtained, Curtiss moved the glycol coolant radiator forward to the chin; its new air scoop also accommodated the oil cooler air intake. Other improvements to the landing gear doors and the exhaust manifold combined to give performance that was satisfactory to the USAAC. Without beneficial tail winds, Kelsey flew the XP-40 from Wright Field back to Curtiss's plant in Buffalo at an average speed of . Further tests in December 1939 proved the fighter could reach .Molesworth 2008, p. 10.

An unusual production feature was a special truck rig to speed delivery at the main Curtiss plant in Buffalo, New York. The rig moved the newly built P-40s in two main components, the main wing and the fuselage, the eight miles from the plant to the airport where the two units were mated for flight and delivery."New Army Warplane Rides a Trailer on Its First Trip to Airport". Popular Mechanics, January 1941, p. 91.

Performance characteristics

The P-40 was conceived as a pursuit aircraft and was agile at low and medium altitudes but suffered from a lack of power at higher altitudes. At medium and high speeds it was one of the tightest-turning early monoplane designs of the war,Higam 2004, p. 3. and it could out-turn most opponents it faced in North Africa and the Russian Front. In the Pacific Theater it was out-turned at lower speeds by the lightweight fighters Mitsubishi A6M Zero and Nakajima Ki-43 Hayabusa (known to Allies as "Oscar"). The American Volunteer Group Commander Claire Chennault advised against prolonged dogfighting with the Japanese fighters due to speed reduction favoring the Japanese.Gunston 1981, p. 68.

Allison's V-1710 engines produced at sea level and . This was not powerful compared with contemporary fighters, and the early P-40 variants' top speeds were only average. The single-stage, single-speed supercharger meant that the P-40 was a poor high-altitude fighter. Later versions, with Allisons or more powerful Packard Merlin engines were more capable. Climb performance was fair to poor, depending on the subtype. Dive acceleration was good and dive speed was excellent. The highest-scoring P-40 ace, Clive Caldwell (RAAF), who claimed 22 of his 28½ kills in the type, said that the P-40 had "almost no vices", although "it was a little difficult to control in terminal velocity".Alexander 2006, p. 22. The P-40 had one of the fastest maximum dive speeds of any fighter of the early war period, and good high-speed handling.

The P-40 tolerated harsh conditions and a variety of climates. Its semi-modular design was easy to maintain in the field. It lacked innovations such as boosted ailerons or automatic leading edge slats, but its strong structure included a five-spar wing, which enabled P-40s to pull high-G turns and survive some midair collisions. Intentional ramming attacks against enemy aircraft were occasionally recorded as victories by the Desert Air Force and Soviet Air Forces.Romanenko, Valeriy and James F. Gebhardt. "The P-40 in Soviet Aviation". Lend-lease on airforce.ru. Retrieved: 7 March 2006. Caldwell said P-40s "would take a tremendous amount of punishment, violent aerobatics as well as enemy action". Operational range was good by early war standards and was almost double that of the Supermarine Spitfire or Messerschmitt Bf 109, although inferior to the Mitsubishi A6M Zero, Nakajima Ki-43 and Lockheed P-38 Lightning.

Caldwell found the P-40C Tomahawk's armament of two Browning AN/M2 "light-barrel" dorsal nose-mount synchronized machine guns and two Browning machine guns in each wing to be inadequate.Alexander 2006, p. 21. This was improved with the P-40D (Kittyhawk I) which abandoned the synchronized gun mounts and instead had two guns in each wing, although Caldwell still preferred the earlier Tomahawk in other respects. The D had armor around the engine and the cockpit, which enabled it to withstand considerable damage. This allowed Allied pilots in Asia and the Pacific to attack Japanese fighters head on, rather than try to out-turn and out-climb their opponents. Late-model P-40s were well armored. Visibility was adequate, although hampered by a complex windscreen frame, and completely blocked to the rear in early models by a raised turtledeck. Poor ground visibility and relatively narrow landing gear track caused many losses on the ground.

Curtiss tested a follow-on design, the Curtiss XP-46, but it offered little improvement over newer P-40 models and was cancelled.Berliner 2011, p. 18.

Operational history In April 1939, the US Army Air Corps, having witnessed the new, sleek, high-speed, in-line-engined fighters of the European air forces, placed the largest fighter order it had ever made for 524 P-40s.

French Air Force An early order came from the French Armée de l'Air, which was already operating P-36s. The Armée de l'Air ordered 100 (later the order was increased to 230) as the Hawk 81A-1 but the French were defeated before the aircraft had left the factory and the aircraft were diverted to British and Commonwealth service (as the Tomahawk I), in some cases complete with metric flight instruments.

In late 1942, as French forces in North Africa split from the Vichy government to side with the Allies, US forces transferred P-40Fs from 33rd FG to GC II/5, a squadron that was historically associated with the Lafayette Escadrille. GC II/5 used its P-40Fs and Ls in combat in Tunisia and later for patrol duty off the Mediterranean coast until mid-1944, when they were replaced by Republic P-47D Thunderbolts.

British Commonwealth

Deployment

In all, 18 Royal Air Force (RAF) squadrons, four Royal Canadian Air Force (RCAF), three South African Air Force (SAAF) and two Royal Australian Air Force (RAAF) squadrons serving with RAF formations, used P-40s."Aircraft of the RAF (M – T)". rafweb.org, 2007. Retrieved: 6 January 2008.rafweb.org, 2007, "Aircraft of the RAF (E – L)". rafweb.org, 2007. Retrieved: 6 January 2008. The first units to convert were Hawker Hurricane squadrons of the Desert Air Force (DAF), in early 1941. The first Tomahawks delivered came without armor, bulletproof windscreens or self-sealing fuel tanks, which were installed in subsequent shipments. Pilots used to British fighters sometimes found it difficult to adapt to the P-40's rear-folding landing gear, which was more prone to collapse than the lateral-folding landing gear of the Hurricane or Supermarine Spitfire. In contrast to the "three-point landing" commonly employed with British types, P-40 pilots were obliged to use a "wheels landing": a longer, low angle approach that touched down on the main wheels first.