The SEV-3 was eventually the progenitor of a family of advanced aircraft including the SEV-3XLR and 2-XP (two-place, experimental) fighter, the BT-8 trainer and SEV-1P (single-seat) fighter. The most radical conversion occurred when the fixed-gear SEV-1P was fitted with a rearward retracting main undercarriage to produce the prototype of the successful P-35A fighter series. The Seversky Aircraft design office led by Seversky was responsible for 25 different innovative projects, many of them "still-born" including the "Seversky Super-Clipper", an eight-engine, 250 ft span transoceanic transport and the four-place, tricycle gear "Seversky Executive" high speed personal aircraft. The Sev-S2, virtually identical to the P-35, which was undergoing trials in 1937, dominated the last three Bendix Trophy air races, beginning in 1937 when Frank Fuller won at an average speed of 415.51 km/h.