After the war, the few military Constellations built (designated C-69) were retrofitted by Lockheed for use in the post-war airline industry as the L-049.

It was then that the United States Air Force (USAF) signed a contract with Lockheed for ten L-749A aircraft designated the C-121A.

The United States Navy (USN) had also placed an order for two AWACS versions of the L-749A designated the PO-1W (later WV-1).

The C-121A versions differed from the L-749 only through having a reinforced floor to handle cargo, and a large aft loading door.

Dwight Eisenhower and General Douglas MacArthur both used the C-121A as their personal VIP transports.

The Navy reduced the number of available seats to fit room for life rafts on overseas flights.

Two modified R7V-1 aircraft were used on Antarctic supply missions while conducting tests and observations at the same time.

Unlike its Naval equivalent, the C-121C featured square cabin windows instead of round ones.

Other features of the C-121C included an Auxiliary Power Unit, Turbo-compound R-3350s, and the ability to carry 75 passengers, 72 fully equipped troops, or 47 stretchers.

One former C-121C flies today with the Historical Aircraft Restoration Society of Australia, and the other flew until 2016 with the Super Constellation Flyers Association of Switzerland.