Boeing Model 307
The aircraft that helped set the stage for several generations of large Boeing commercial designs, as well as leaving its own mark as the first pressurized airliner, the Stratoliner flew in late December 1938 as a passenger outgrowth of the B-17C. This combined a new, larger fuselage with the Fort’s wing, tail, and engines, and was intended for high-altitude, long distance work with Pan Am and TWA. The initial prototype, NX19901, had a short life, being lost in March 1939 when rudder lock on a test flight resulted in a fatal spin. This resulted in a redesign of the vertical tail that was also applied to the 307’s bomber progenitor, starting with the B-17E.
The five TWA 307s were taken over by the USAAF as C-75s shortly after the US entered WWII, being used for priority transatlantic missions. The C-75s had their pressurization systems and several seats removed, and additional fuel tankage fitted. The C-75s were returned to TWA control in 1944, and rebuilt by Boeing with B-17G type wings as well as B-29 derived electrics.