The D prototype was offered to the US Army Air Service at the end of 1918. It was a two-bay biplane of all-wood construction, covered with fabric. It was powered by a 300 hp (224 kW) Hispano-Suiza engine. The pilot of the first flight test, Clarence B. Coombs, gave it a positive evaluation: "This aircraft performs better than the Sopwith Camel and Snipe, the Thomas-Morse, the Nieuport and Morane Parasol, the Spad and S.V.A." The military ordered 50 production aircraft, but put the production order up for bidding. Curtiss Aircraft entered the lowest bid and built the fighter, modifying it slightly with a wider wingspan and redesigned ailerons. The first Curtiss Orenco D flew on 26 August 1921.