The Curtiss P-40 Warhawk evolved from the earlier Curtiss Hawk 75 (P-36 in American service). This radial engine powered fighter first flew in April 1935, and in 1937 was purchased by both the USAAF and the French. However, it soon became clear that the P-36 would not be able to compete with the best fighters being developed in Europe, such as the Supermarine Spitfire or Messerschmitt Bf 109. Accordingly it was decided to replace the radial engine with an Allison chemically cooled in-line engine. The first attempt to achieve this, the XP-37, suffered from poor visibility and an unreliable supercharger.
Work on the XP-40 began in 1938. This would use a modified P-36 fuselage, with the Allison V-1710-19 inline engine, producing 1,050 hp at 10,000 feet. Tests suggested the new aircraft would be fast, but at a relatively low altitude. Work on the prototype began under the terms of a contract issued on 30 July 1938. It first flew on 14 October 1938. The following January the XP-40 won a fighter contest, and the USAAF placed an order for 524 P-40s.
However, the new aircraft did not live up to expectations. Top speed was only 340 mph, twenty miles per hour slower than Curtiss had promised. It would take all of 1939 to fix this problem, until in December 1939 the XP-40 reached 366 mph at 15,000 feet. This put its top speed on a par with the Spitfire I, but at a much lower altitude – the Spitfire peaked at 18,500 feet. The P-40 was now ready to enter full production. The P-40, or Curtiss Hawk H-81, entered production in March 1940. It was thus the most modern fighter available to the USAAF when American entered the Second World War.
The first 199 aircraft produced were simply designated P-40s. They carried two .50 calibre machine guns in the engine cowling, and one .30 calibre machine gun in each wing. The engine was an Allison V-1710-33, producing 1,090 hp. During the production run a second .30 calibre machine gun was added to each wing, giving the P-40 six guns. The production aircraft had a top speed of 357 mph at 15,000 feet, commendably close to that produced by the prototype. 200 of the initial order of 524 were produced before the order was deferred to allow Curtis to build 142 Hawk 81s for the French. This aircraft did not arrive in time for the battle of France, and were instead delivered to Britain, where they were known as Tomahawks.
When USAAF production resumed after the French order, the designation was altered to P-40B. This version adopted pilot armour, a bullet proof windscreen and self-sealing fuel tanks. These changes had to be made on just about every American aircraft in production at the time. The P-40B (Hawk H-81 A-2) could also carry bombs under each wing. The USAAF received 131 P-40Bs. Production of the P-40B began in January 1941, and ended in April of the same year.
The P-40C was the final Hawk 81 model (H-81 A-3). The main change was the addition of an extra fuel tank, capable of carrying 134 gallons. The P-40, P-40B and P-40C were known in RAF service as the Tomahawk, and also equipped the famous Flying Tigers in China. 193 P-40Cs were built for the USAAF, and were delivered between March and April 1941.
The P-40D saw a series of major changes to the aircraft. It used the Allison V-1710-39 engine, which offered more power at higher altitudes than the earlier engines. The two .50 calibre machine guns from the nose were moved to the wings, with the four .30 calibre guns. The type could also carry two 20mm cannon. The most obvious visual change saw the radiators moved forward, giving the aircraft its familiar “shark mouth” appearance. The amount of ammunition carried was increased to 615 rounds per gun. The P-40D could carry one 500lb bomb under the fuselage. Both Curtis and the RAF acknowledged the importance of these changes with a change of designation – Curtis to Hawk 87A, and the RAF to Kittyhawk. However, only 42 P-40Ds were built, 22 for the USAAF and 20 for the RAF.
The main change made for the P-40E (Hawk 87A-3) was the replacement of all of the .30 calibre guns with .50 calibre machine guns. This gave the P-40E a total of six .50 calibre machine guns. Eight hundred and twenty of this model were produced for the USAAF.
This refers to 1,500 P-40Es produced to be supplies to the British under lend-lease. This type served with a variety of Commonwealth air forces as the Kittyhawk IA.
The P-40F (H-87D) saw a major change of engine, to the Packard Merlin XX. Otherwise the P-40F was very similar to the P-40E. During the production run the fuselage was made two feet longer, improving directional stability. In RAF service this was known as the Kittyhawk II. The Merlin engine gave the P-40 much better high altitude performance – the Allison engine lost power above 15,000 feet, the Merlin kept going to 19,000 feet.
The P-40K was developed from the P-40E. The main change was the use of the Allison V-1710-73 engine. The extra power this gave caused the same problems as had been faced in the P-40F. The first reaction was to increase the size of the dorsal fin, but later in the production run the longer fuselage used in the P-40F was adopted. The USAAF took delivery of 1,300 P-40Ks. The RAF received 21 of these aircraft as Kittyhawk IIIs.
This was a development of the earlier P-40F, retaining the Packard Merlin. A great deal of effort went into reducing the weight of the aircraft, and indeed 450 lbs was removed. Amongst the changes was the removal of one gun from each wing, giving the P-40L a total of four wing mounted guns. However, the hoped for increase in speed did not materialise – the P-40L was only 4 mph quicker than the P-40F. The RAF retained the Kittyhawk II designation for this version. Later production P-40Ls could carry rockets under the wings.
The P-40M (Kittyhawk III) was intended for the RAF. It resembled the P-40K, with a Allison V-1710-81 engine and six .50 calibre machine guns.
This version was produced in greater numbers than any other. 5,219 P-40Ns (Hawk H-87Ws) were built before production ended on 30 November 1944. It used the same Allison V-1710-81 engine as the P-40M. Like the P-40L, the number of guns was reduced to four, and other weight saving measures were taken. The result was a much improved top speed of 378 mph. During the production run the lost guns were replaced – in the fighter bomber role the added firepower mattered more than that last bit of speed.
This was the final prototype P-40. It used a much more powerful Allison V-1710-121 engine, providing 1,425 hp. In tests it reached a top speed of 422 mph and 20,000ft, a great improvement on any earlier P-40. However, by that point in the war the Spitfire and Mustang offered much better performance, and the P-40Q was not developed any further.
Introduction - P-40 Variants - Kittyhawk - Tomahawk - P-4o in American Service - Statistics