Ko da yake an gabatar da C-141 Starlifter, jami'ai sun yi imanin cewa ana buƙatar jirgin sama mafi girma da kuma iyawa, musamman don ɗaukar kaya wanda ba zai dace da kowane jirgin sama na yanzu ba. Waɗannan karatun sun haifar da buƙatun farko don CX-Heavy Logistics System (CX-HLS) a watan Maris na 1964 don jirgin sama mai ɗaukar nauyin 180,000 fam (81,600 kg) da saurin Mach 0.75 (500 ko 800 km / h), da kuma ba tare da tanadi ba 5,000 nautical miles (9,300 km) tare da nauyin nauyin 115,000 fam (52,200 kg). Ya kamata a yi amfani da nauyin da ya kai 17 feet (5.18 m) da 13.5 feet (30 m) da 100 feet (100 m) tare da ƙofofi a gaban da kuma baya.
Boeing, Douglas, da kuma Lockheed