The Curtiss Aeroplane and Motor Company had established a continuing relationship with the US Army, which had got off to a good start in 1914 with the then large scale procurement (94) of the first of the classic JN (Jenny) series. Twenty years later, when the Curtiss Aeroplane Company had become a division of the Curtiss-Wright Corporation, it was decided to design and develop as a private venture a new monoplane pursuit (fighter) aircraft. Known as the Curtiss Model 75, it had such advanced features as retractable landing gear and an enclosed cockpit for the pilot, and the company believed that the US Army would be prepared to consider it as a replacement for the lower performance Boeing P-26.

Contemporary with the famous wartime triad of the Messerschmitt Bf 109, Hawker Hurricane and Supermarine Spitfire, it failed to emulate their performance, for at that era of fighter development designers had not yet succeeded in realising the full potential of bluff, radial air-cooled engines. At a later date an attempt was made to upgrade the Model 75 by the installation of an Allison V-1710 turbocharged inline engine, but the prototype and a hatch of service test YP-37s with the V-1710-21 engine failed to achieve a sufficiently high standard of performance and were, in any event, superseded by the P-40.

The Model 75 prototype, powered by a 900 hp (671 kW) Wright XR-1670-5 radial engine, was submitted to the US Army Air Corps in May 1935 for evaluation in a design competition for a single-seat pursuit aircraft. This failed to materialise because no competing designs were ready, and it was not until April 1936 that the twice-postponed contest began. By then the Model 75 had been re-engined with an 850 hp (634 kW) Wright XR-1820-39 Cyclone radial, and was identified as the Model 75B with this powerplant.

The Seversky Aircraft Corporation won the USAAC's competition with a not-too-dissimilar aircraft, which was ordered into production as the P-35. However, Curtiss were awarded a contract for just three examples of their design, to be powered by a derated version of the 1,050 hp (783 kW) Pratt & Whitney R-1830-13 Twin Wasp radial engine, and to be used for test and evaluation under the designation Y1P-36. By comparison with the original Model 75 prototype, these had cockpit modifications to improve fore and aft view, and introduced a retractable tailwheel. A feature of the main landing gear units was that they swivelled through 90' as they retracted aft, so that the main wheels could lie flush in the under-surface of the wing.

Service testing of the Y1P-36s was considered so successful that a contract for 210 production P-36As was awarded on 7 July 1937, then the US Army's peacetime contract for pursuit aircraft. Delivery of these began in April 1938, but by late 1941 when the United States became involved in World War 11, they Were already considered obsolete. Circumstances compelled limited use of the P-36As in the opening stage of hostilities with Japan, but they were very soon relegated for use in a training role.

Variants included a single XP-36B with a 1,000 hp (746 kW) Pratt & Whitney R-1820-25 engine, and the last 31 of the original production run were completed as P-36Cs with a more powerful Twin Wasp engine. The designation XP-36D/-36E/-36F were applied to experimental examples with differing armament.

Examples of the H75A export (Hawk) model were supplied to the French Armee de L'Air as H75-A1/-A2/-A3/-A4 fighters with different engines and armament, but the majority were transferred to the UK after the fall of France; being designated respectively Mohawk Mks I/II/III/IV. H7SA-5 was the designation of a model to be assembled in China by the Central Aircraft Manufacturing Company. After a few aircraft had been built in China, the company was transferred to India as Hindustan Aircraft Ltd, and its H75A-5s were accepted by the RAF as Mohawk Mk IVs. The type was supplied to Norway which ordered initially 24 of the H7SA-6 model, followed by 36 of the H7SA-8. The latter were not delivered to Norway, six being handed over to Free Norwegian forces in Canada following German occupation of Norway and the remaining 30 requisitioned for service with the USAAC under the designation P-36G. The Netherlands ordered 20 of the H7SA-7 model, these being delivered to the Netherlands East Indies, and Persia (now Iran) ordered 10 examples of the H75A-9. Hawks also served, indirectly, with the air, forces of Finland, India, Peru, Portugal, South Africa and Vichy France.

Variants

Model 75: original company designation for the prototype, powered by a 900 hp (671 kW) Wright XR-1670-5 radial engine.

Model 75B: same as above but with a 850 hp (634 kW) Wright R-1820 radial engine.

Y1P-36 (Model 75E): three test and evaluation aircraft powered by a derated 1,050 hp (783 kW) Pratt & Whitney R-1830-13 Twin Wasp radial engine.

P-36A (Model 75L): first production batch of 210 aircraft ordered on 7 July 1937.

P-36B: a sinlge aircraft with a 1,000 hp (746 kW) Pratt & Whitney R-1830-25 radial engine.

P-36C: the last 31 aircraft on the P-36B production line were given a higher rated Pratt & Whitney radial engine and two 7.62 mm (0.30 in) machine guns and re-designated P-36Cs.

XP-36D/36E/36F: experimental examples with various armament.

Hawk 75A: export aircraft sold to the Armee de l'Air as H75-A1/-A2/-A3/-A4 fighters with different engines and armament. With the fall of France most were transferred to the British as Mohawk Mks I/II/III/IV.

Hawk 75A-5: the designation of a model to be assembled in China by the Central Aircraft Manufacturing Company. After a few aircraft had been built in China, the company was transferred to India as Hindustan Aircraft Ltd, and its H75A-5s were accepted by the RAF as Mohawk Mk IVs.

Hawk 75A-6: 24 aircraft ordered by Norway.

Hawk 75A-7: 20 aircraft ordered by the Netherlands and shipped to the Netherlands East Indies.

Hawk 75A-8: 36 aircraft ordered by Norway but after the German occupation six were turned over to Free Norwegian Forces in Canada.

Hawk 75A-9: 10 aircraft ordered by Persia, now Iran.

P-36G: designation given to the remaining 30 H75A-8 aircraft that were turned over to the USAAC.

Model 75J: designation of Model 75A demonstrator fitted with a mechanical supercharger for its R-1830 engine.

Model 75K: unrealised project for a version with the Pratt & Whitney R-2180 Twin Hornet.

Model 75R: the above project finally produced by the conversion of the Model 75A demonstrator.

Curtiss Hawk 75: The belief that there would be a market for a less sophisticated export version of the Curtiss Model 75 led to development in 1937 of such a version, known as the Curtiss Hawk 75. Two Hawk 75H demonstrators were built, these being generally similar in construction to the Y1P-36 but having a lower-powered Wright radial engine and fixed tailwheel type landing gear.

The original demonstration model was bought by the Chinese Nationalist government during 1937, and was followed in 1938 by an order for an additional 112 aircraft under the designation Hawk 75M to equip the new reorganised Chinese air force. In 1938 the delivery of 12 similar aircraft for the Royal Siamese air force began. Designated Hawk 75N, they differed by being armed with two additional machine guns and were used briefly in combat during 1941. Production of the Hawk 75O for Argentina, which had acquired the second demonstrator, totalled 29 aircraft. This nation also negotiated with Curtiss a licence to build the type and 20 were produced from 1940 in a government aircraft factory at Cordoba. The Hawk 75Q, of which two were built, was another demonstrator model: one, converted with a retractable landing gear was given to Claire Chennault by Madame Chiang Kai-shek and the other had fixed landing gear but crashed in China during 1939.  

SPECIFICATIONS
Span: 37 ft. 4 in.
Length: 28 ft. 6 in.
Height: 8 ft. 5 in.
Weight: 5,650 lbs. loaded
Armament: Two .30-cal. or two .50-cal. machine guns
Engine: Pratt & Whitney R-1830 of 1,050 hp.
Cost: $23,000