the origins of the p-35 can be traced back to the seversky sev-3 three-seat amphibian, designed by alexander kartveli, seversky's chief designer and seversky's first aircraft. the sev-3 first flew in june 1933 and was developed into the seversky bt-8 basic trainer, 30 of which were ordered by the united states army air corps (usaac) in 1935. this proved grossly underpowered and was quickly replaced by the north american bt-9.