The Stratofreighter was the transport derivative of the B-29 Superfortress. It was first flown on November 15th, 1944 and was followed by ten service test model YC-07's. Clamshell doors were fitted to the rear fuselage and built-in ramps could be lowered to allow vehicles to be driven straight in. They were powered by 4 Wright R-33350-57a piston engines and accommodation was provided for 134 troops or stretcher cases with 4 attendants.