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The Curtiss Model 75R was the third designation given to a Curtiss-owned Hawk that was used to test external superchargers. This aircraft, with the civil registration NX 22028 and Curtiss c/n 12931, had originally been a company-owned Model 75A demonstrator. It then became the Model 75J when it was equipped with an external mechanical supercharger.
Late in 1938 the aircraft was given a new supercharger. This had the supercharger mounted below the nose, just behind the engine cowling, and the intercooler under the trailing edge of the wing. In January 1939 this aircraft, as the Model H75R, was submitted to the US Army, but lost out to a turbo-supercharged Seversky XP-41, which entered production as the P-43.