Early in 1937, Curtiss began the development of a simplified version of the Y1P-36 intended specifically for export. Curtiss was aware that some potential customers whose air arms operated under relatively primitive conditions would look askance at a sophisticated feature such as a retractable undercarriage which promised to afford difficult maintenance problems. The "simplified Hawk" project was given the company designation of Model 75H.
The construction of the Model 75H was similar to the Y1P-36, but a lower-powered engine was provided and a fixed, single-strut undercarriage with streamlined fairings was fitted. These modifications were first applied to a demonstrator aircraft which was re-engined with a Wright Cyclone GR-1820-GE rated at 875 hp for takeoff. This airplane was given the civil registration of NR1276, and publicized in Curtiss sales brochures as "Hawk 75". Emphasis was placed on ease of maintenance, rough field performance, and the amenability of the aircraft to accommodate different brands of engines and different types of armament in order to suit the customer's individual requirements.
A second and more definitive demonstrator aircraft was built which differed from its predecessor in some respects, including the adoption of the more deeply-scalloped decking immediately aft of the cockpit and revised windshield arch and canopy framing. Armament was supplemented by an additional pair of 0.30-cal machine guns in the wings, firing outside the propeller arc. Provision was made for the attachment of underwing bomb racks capable of carrying ten 30-lb or six 50-lb bombs, plus a centerline rack for a single 500-lb bomb. This aircraft was given the civil registration of N1277.
The first 75H carried the US civil registration of NR-1276. It was sold to China. The Chinese government presented this airplane to General Claire L. Chennault for his own personal use. The second one was registered as NR-1277 and was sold to Argentina.
The first overseas customer for the Hawk 75 was the Chinese Nationalist government, which ordered a total of 112 Hawk 75 non-retractable undercarriage models with R-1820 Cyclone engines and four 0.30-in guns (two in the fuselage and two in the wings). These planes were to be built by Curtiss and delivered as major components to the Central Aircraft Manufacturing Company at Loi-Wing, where they would be assembled and delivered to Chinese units. These airplanes were retroactively assigned the designation Hawk 75M by the Curtiss company. Aside from the additional wing guns and some minor revisions to the undercarriage fairings, these planes were identical to the second "simplified Hawk" demonstrator.
The Hawk 75M was powered by an export-approved 875 hp Wright GR-1820-G3 Cyclone radial. Wingspan was 37 feet 0 inches, length was 28 feet 7 inches, and wing area was 236 square feet. Empty weight was 3975 lbs, and gross weight was 5305 lbs. Maximum speed was 280 mph at 10,000 feet, service ceiling was 31,800 feet, and range was 1210 miles with fuel overload. Armament was four 0.30-in machine guns--two in the nose and two in the wings.
It is uncertain just how many Hawk 75Ms actually ended up in Chinese service. Only 30 Hawk 75Ms are accounted for in Curtiss records, with deliveries beginning in May of 1938. Tooling and kits for an unspecified number were delivered to the Central Aircraft Manufacturing Company Wing for assembly in China, and an unspecified number were built there. Three full squadrons of Model 75Ms are known to have been operational. These fighters achieved few successes against the Japanese forces, largely owing to poor serviceability and the inadequate training of both pilots and ground crews.
The government of Siam (Thailand) also exhibited interest in the Hawk 75, and ordered somewhere between 12 and 25 examples (the exact number is uncertain, and depends on which source you pick). These were given the designation Hawk 75N by Curtiss, and were generally similar to the Chinese Hawk 75Ms except for some minor revisions to the undercarriage mainwheel fairings and some differences in the armament. Sources also differ in the armament fitted--one claims that the armament was two nose guns (one 0.30-in and one 0.50-in nose guns and four 0.30-in guns in the wings, another claims that that there were two 23-mm Danish Madsen cannon housed in detachable underwing fairings.
Twelve Hawk 75Ns were delivered to Siam (Thailand) starting in November, 1938. They These Hawk 75N fighters were involved in the Thai invasion of Indo- China in January 1941, the first recorded combat taking place on January 11 when four 75Ns escorted nine Martin 139-Ws in an attack on the French airfield at Nakorn Wat. The formation was intercepted by four French Morane-Saulnier M.S.406s. In the resulting air battle, the Thai Hawks claimed two Morane fighters shot down (although the claim was later refuted by the French). On December 7, 1941, the Thai Hawks were in action once again, this time against invading Japanese forces. In the brief battle, one third of the serviceable Hawks were destroyed. Those not destroyed were taken over by the Japanese. One example is now in the Royal Thai Air Museum in Bangkok.
After purchasing the NR1277 75H demonstrator (c/n 12328) from Curtiss, the Argentine government ordered twenty-nine production examples of the non-retractable undercarriage Hawk 75 with 875 hp Cyclone engines. Designated Hawk 75O by the Curtiss company, these planes had a similar undercarriage to the Thai Hawk 75N and featured a redesigned engine exhaust system with a semi-circle of electrically-operated gills at the rear of the cowling. Armament consisted of four 7.62-mm Madsen machine guns. The first Hawk 75O was completed by Curtiss in late November, 1938. The planes were serialed C-601 through C-630.
Maximum speed was 239 mph at sea level and 280 mph at 10,700 feet. Initial climb rate was 2340 ft/min. An altitude of 23,000 feet could be attained in 12.52 minutes. Service ceiling was 31,800 feet. Empty and loaded weights were 3975 lbs and 5172 lbs.
At the same time, Argentina acquired a license to manufacture the Hawk 75O at the Fabrica Militar de Aviones. The first FMA-built Hawk was delivered on September 16, 1940. A total of 20 was built, with serials being C-631 to C-650. Some of these Hawks remained in service for over a decade, the last ones operating from El Plumerillo in western Argentina until 1953, when they were transferred to training units until being withdrawn during 1954.
Model 75Q was the designation assigned to two additional non-retractable undercarriage demonstrators with R-1820 engines. One was converted to retractable undercarriage configuration and was presented to Madame Chiang Kai-Shek. She gave the plane to General Claire Chennault who was then reorganizing the Chinese Air Force. The other was flown as a demonstrator in China by American pilots but crashed after takeoff on May 5, 1939.