Uncertain Wings: Curtiss Hawk 75 in China

By Richard L. Dunn © 2008

     At the outbreak of the Sino-Japanese conflict in July 1937 the Curtiss-Wright Corp. was already well established in China. It had exported over one hundred Hawk biplane fighters to China and also had part ownership in an aircraft production company (CAMCO) that produced licensed built versions of the same aircraft and manufactured or repaired other models. Curtiss biplane fighters made up a substantial part of China’s air power and were able to compete on roughly equal terms with the Japanese army and navy biplane fighters at the beginning of the conflict.

     The first months of the war saw Chinese air power suffer from combat and operational losses. The Japanese navy was receiving a new fighter. The first of their new Type 96 fighters arrived in China several weeks after the fighting started. The performance of the monoplane Type 96 was significantly better than any of the available Chinese fighters. The Chinese needed more and better fighters. China sought help to bolster its aviation capability from a variety of sources including its established supplier the Curtiss-Wright Corp.

     In mid-August 1937 China purchased a demonstration model of the Curtiss Hawk 75 upon the recommendation of Lt. Col. Claire L. Chennault, air advisor to Generalissimo Chiang Kai Shek. The Hawk 75 demonstrator was an export version of the P-36 fighter (Curtiss designation Hawk 75A) being acquired by the U.S. Army Air Corps. The P-36 was not then available for export but the Hawk 75 version with fixed rather than retractable landing gear and certain other changes of equipment was. The Chinese made a preliminary decision for the purchase of thirty Hawk 75’s plus purchase of additional Hawk III biplanes with Chennault’s blessing on August 24, 1937. Detailed negotiations to complete the contract then took place. Dr. H.H. Kung represented the Chinese government and apparently William D. Pawley, President of CAMCO and Curtiss-Wright representative in China, negotiated for Curtiss.

     The Hawk 75/P-36 originated as a privately financed venture of Curtiss that competed for an Air Corps contract in 1935 but lost to the Seversky P-35 which received a production contract for 77 aircraft in 1936. Curtiss presented a revised version (Y1P-36) which caught Air Corps attention and eventually (July 1937) received a production contract for an unprecedented 210 aircraft of which the first was delivered in April 1938. Export versions of the P-36 later performed creditably for the French in 1939-40. Though becoming somewhat dated P-36’s intercepted the Japanese over Hawaii in December 1941; flew for the Dutch in the East Indies in 1942; and, were for a time in 1942 the sole British fighter defense over Assam (India) and soldiered on in various roles in the Burma campaign through 1943. In addition to its other service it is perhaps ironic that the Hawk 75 also flew against America’s Allies. The Finns flew captured Hawks against the Russians and the Germans used a number of them as training aircraft.

Hawk Demonstrator. Curtiss began development of the export version of their model 75 early in 1937. In its original form the demonstrator had less power, fixed landing gear and was simplified as much as possible both to accommodate export concerns and to make it suitable for operations from airfields with austere facilities. Powered by a Curtiss-Wright GR-1820-G3 engine (875 h.p. for take off) another selling point for the Hawk 75 was the fact that it could be equipped with a variety of engines.

     The Hawk 75H flown in China bore U.S. civil registration No. NR1276. It was maneuverable, had a service ceiling of 31,800 feet, and, credited with a maximum speed of 280 m.p.h. at 10,700 feet was far faster than Japanese biplane fighters. It even had an edge on the Type 96 Carrier Fighter just entering service with the Japanese. NR1276 was considered eminently satisfactory for service in China. After its purchase it was often flown personally by Chennault. The production order for thirty additional Hawks was concluded in late summer 1937.

     More than a year later two additional demonstrator aircraft were produced. They bore the designation Hawk 75Q. With its R-1820-G105A engine this version had in excess of 200 more horse power than the earlier demonstrator. This aircraft was fitted with under wing gun pods for cannon. Some published accounts say two Hawk 75Q’s were supplied to China with fixed landing gear but one was converted to retractable gear. Only one Hawk 75Q was involved in official trials in the spring of 1939 and it had retractable landing gear. In fact it was routinely referred to as a P-36.  

Hawk 75M. According to Chennault as the contract for the Chinese Hawks (Hawk 75M) was being finalized Bruce Leighton of CAMCO and employees of Curtiss-Wright then in Nanking with the demonstrator aircraft asked Chennault for any suggestions that would improve the performance of the Hawk for service in China. Chennault recommended lowering the canopy to better suit Chinese pilots, redesigning the windshield for better visibility, providing a larger battery, and changing the wheel fairing slightly to improve drainage. Later it was determined that Chennault’s suggestion to lower the canopy would delay production. Chennault advised that early delivery was paramount and no modification that would delay delivery was acceptable. Chennault was also advised that larger wheels (and hence larger wheel fairings) would be installed to accommodate operations from muddy airfields. The Hawk 75M incorporated a machine gun in each wing in addition to the nose deck armament of the P-36.  

     When the first Hawk 75M’s arrived in China in the middle of 1938 they proved to be a disappointment. There followed one of several squabbles involving Chennault and Bill Pawley that were to characterize their relationship. Pawley and the CAMCO/Curtiss side alleged that Chennault demanded changes in the Hawk 75 as a precondition to execution of the contract. Chennault countered that he had merely made suggestions. Chennault asserted that most of the deficiency in speed was due to the production aircraft having a critical altitude 3,000 feet lower than the demonstrator. Pawley pointed to Chennault’s changes in the aircraft’s configuration and equipment as the fault.

     Virtually all sources indicate that the demonstrator and production Hawk 75 had the same engine the GR-1820-G3 (the Y1P-36 was equipped with a Pratt and Whitney R-1830 engine). Chennault’s claim of a major difference in critical altitude is hard to credit if the same engine was used in both versions although changes in the exhaust system were later made. Most likely the deficiency in performance was caused by the cumulative effect of the various changes between the demonstrator and production aircraft.