Completed late in 1938 as a company-owned demonstrator, the Hawk 75-R was essentially similar to the USAAC's P-36A. Its Pratt & Whitney R-1830-19 (SC2-G) Twin Wasp was, however, fitted with a turbo-supercharger mounted beneath the nose, just aft of the engine cowling, with a ventrally-mounted intercooler. Extensively tested by the USAAC, the Hawk 75-R was eventually returned to Curtiss as the turbo-supercharger proved unreliable and the manual monitoring of the unit was considered impracticable in combat. The turbo-supercharger was subsequently removed and the aircraft re-engined with a Cyclone.