The YC 14 and YC 15 competition to replace the C130 in the 70's, sticks in my mind for some obscure reason
Well, it's stuck there for the wrong reason - the YC-14 and YC-15 competition led to the C-17, (eventually) At least 1 of the YC-15s survives in the 'boneyard' at Davis Monthan AFB