From the wiki: “With the end of the war, the Air Transport Command found itself in limbo. Senior USAAF authorities considered ATC to be a wartime necessity that was no longer needed, and expected its civilian personnel, including former airline pilots, to return to their peacetime occupations. Senior ATC officers, on the other hand, thought that ATC should be developed into a national government operated airline, an idea that was soundly opposed by the airline industry. While the war had firmly established the necessity of a troop carrier mission, most military officers believed the role performed by ATC should be provided by contract carriers.
“When the United States Air Force was established as a separate service in 1947, the Air Transport Command was not established as one of its missions. The ATC commander and his staff took it upon themselves to convince the new civilian leadership of the newly created Department of Defense (DOD) (and Secretaries of the Army and Air Force) that ATC had a mission. They seized upon testimony by former Troop Carrier Command commander Major General Paul Williams that the Air Force should have a long-range troop deployment capability, and began advocating that ATC transports could be used to deploy troops. Williams had been pressing for the development of a long-range troop carrier airplane when he made his statement.
“The DOD believed it should have its own air transport service and decided that ATC should become the Military Air Transport Service, supported by the USAF, even though not listed as a formal military mission. When the ATC commander wrote a mission statement for the proposed new command he inserted ‘deployment of troops’ as a mission, although the change had never been formally requested, the Secretary of the Air Force either allowed it to remain or overlooked it when signing the mission statement.”