McDonnell Douglas YC-15
It was McDonnell Douglas' entrant into the United States Air Force's Advanced Medium STOL Transport ( AMST ) competition to replace the Lockheed C-130 Hercules as the USAF's standard STOL tactical transport . 
<triplet> United States Air Force <subj> Lockheed C-130 Hercules <obj> item operated <triplet> Advanced Medium STOL Transport <subj> McDonnell Douglas <obj> manufacturer