Designed by Donovan R Berlin to participate in a USAAC fighter contest scheduled to take place on 27 May 1935, the Model 75 (the retroactive assignment of Model numbers to earlier designs was attempted at this time and the new fighter became the first design to receive a Curtiss Model designation from the outset) all-metal single-seat fighter was initiated in October 1934, flying on 15 May 1935. Featuring a monocoque fuselage and a multi-spar wing, the Model 75 was powered by a 900hp Wright XR-1670-514-cylinder tworow radial. Proposed aimament comprised one 12.7mm and one 7.62mm machine gun. The unsatisfactory behaviour of the Wright engine resulted in its replacement by a 700hp Pratt & Whitney R-1535 Twin Wasp Junior. This, too, proved troublesome and was succeeded by a 950hp Wright XR-1820-39 (G5) Cyclone nine-cylinder radial with which the prototype became the Model 75B. During USAAC trials, the Model 75B took second place to the Seversky SEV-1XP, which was to enter production as the P-35.