Curtiss P-40C Tomahawk, P-40E-1 Warhawk

Last of the famous Hawk line, the Curtiss P-40 Warhawk has always been something of an enigma. By no stretch of the imagination could it be numbered among the 'great' fighter aircraft of World War II. Yet, with the exceptions of the Republic P-47 and North American P-51, it was the most extensively built US fighter, with 15,000 delivered before production ended in December 1944.

Evolution towards the aircraft which the company designated the Model 81 began in 1937, when the Model 75 prototype's airframe was modified to accept a 1,150 hp (858 kW) Allison V-1710-11 inline. In this form the Model 751 became the first American fighter capable of a speed exceeding 300 mph (483 km/h). The Model 751 was evaluated by the USAAC as the XP-37: despite engine and supercharger difficulties, the potential of the design was clear, and the service ordered 13 of the YP-37 service test models with the improved V-1710-21 engine and slightly longer fuselage. The new B-2 supercharger was also fitted, but all YP-37s continued to suffer problems with the powerplant installation.

A little later the tenth P-36A was re-engined with a 1,160 hp (865 kW) Allison V-1710-19 engine, instead of the 1,050 hp (783 kW) Pratt & Whitney R-1830-13 radial which was standard. In other respects it varied little from the P-36A when it was flown for the first time on 14 October 1938. In May 1939 this Model 75P, by then designated XP40, was flown in competition against other pursuit prototypes and was selected for production as most closely meeting US Army Air Corps requirements. A total of 524 P-40 production aircraft (Model 81) were ordered on 27 April 1939, this then representing the largest single order for fighters to originate from the US Army. Just over a year later, in May 1940, the first P-40s began to come off the production line, the initial three being used for service trials. These differed from the initial XP-40, with a less powerful supercharged Allison V-1710-33 engine installed and two 7.62 mm (0.30 in) machine guns in the wings to supplement the two 12.7 mm (0.50 in) machine guns mounted in the fuselage nose. By September 1940 a total of 200 of these aircraft had been delivered to the USAAC.

Before that, in April 1940, production priority had been accorded to delivery of 185 generally similar Hawk 81-Al fighters ordered by France. None, however, left the assembly line before that nation's collapse and, instead, these aircraft were diverted to the UK where they were designated Tomahawk Mk 1. Deliveries to England and to Takoradi in West Africa, began in late 1940, but the Tomahawk was unsuited for operational employment in Europe and the majority were relegated to training duties.

The next version for the RAF (Hawk 81-A2) was designated Tomahawk Mk IIA and this, basically the same as USAAC's P-40B (Model 81-B), had self-sealing fuel tanks, armor, and was armed with two wing-mounted 7.7 mm (0.303 in) machine guns. Unfortunately, the increased weight resulting from these improvements reduced performance, while improved self-sealing tanks and the addition of two more wing guns on the P-40C brought a further erosion of performance. A total of 930 of this version was built for the RAF (Hawk 81-A3), those which entered service being designated Tomahawk Mk IIB. These had US radio equipment but were armed with six 7.7 mm (0.303 in) machine guns. A total of 100 of the allocation of Hawk 81-A3s for the RAF was diverted to China, 90 of these reaching the American Volunteer Group (AVG) operating from Kunming and Mingaladon; 49 shipped direct from the USA, plus 146 reshipped from Great Britain, were supplied to the Soviet Union, and a small number went to the Turkish air force.

Some American P-40s were modified in 1941 to serve in a reconnaissance role, under the designation RP-40, but Curtiss had already begun redesign of the Hawk 81-A in an attempt to improve its performance and effectiveness. The changes included installation of the 1,150 hp (858 kW) Allison V-1710-39, which could maintain this power output to an altitude of 11,700 ft (3565 m), and the addition of armor, provision of four 12.7 mm (0.50 in) wing-mounted machine guns, and an under fuselage hardpoint for the carriage of a 500 lbs (227 kg) bomb or 52 US gallon (197 litre) fuel drop tank. First flown on 22 May 1941 as the Kittyhawk Mk I, having been ordered as such by the UK, it was identified as Hawk 87-A2 by Curtiss, and as the P-40D by the USAAC, which had also ordered this version in September 1940. Only the first 22 aircraft delivered to the USAAF had the armament of four wing-mounted guns, subsequent deliveries having six guns and the designation P-40E (Model 87-B2). A total of 1,500 of this version, identified as the P-40E-1 (Hawk 87-A3 and -A4), was procures by the USAAF for supply to Britain under Lend-Lease, the model being designated Kittyhawk Mk IA in RAF service; in addition large numbers of this version were supplied to British Commonwealth air forces. Other P-40Es were supplied to Brigadier General Claire Chennault's AVG in China where deployed with considerable skill, the P-40 in several variants achieved notable success against Japanese aircraft. A few P-40Es were converted as two-seat trainers, losing their fuselage tank to provide space for the second cockpit.

Throughout the next three years Curtiss made tremendous efforts to improve the capability of the P-40, resulting in a number of variants. Despite all the effort, which resulted in quite considerable improvement, it left performance of the Warhawk below that of contemporary Allied and Axis fighters and production ended in December 1944.

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