The YC-15 was the less radical of the two short take-off and landing (STOL) tactical transports that competed in the 1970s USAF’s Advanced Medium STOL Transport (AMST) competition to replace the Lockheed C-130 Hercules. As it competitor, the Boeing YC-14, the YC-15 proved to be more than a technical success, but changes in operational policy – a turn to strategic instead of tactical uses- condemned both designs to remain just as prototypes. Not all was wasted, the YC-15 formed later the basis of nowadays Boeing C-17 Globemaster III.
This aircraft exemplifies what I “love” about nowadays aviation design: the glorious era of “copy & paste” design. Just take a look a these “Fin-Clones”: