The Sikorsky S-42 was a commercial flying boat designed and built by Sikorsky Aircraft to meet requirements for a long-range flying boat laid out by Pan American World Airways  in 1931. The innovative design included wing flaps, variable-pitch propellers, and a tail-carrying full-length hull. The prototype first flew on 29 March 1934. Here's a photo from my personal collection from the first flight: NC-822M, "Brazilian Clipper"