The C-121A versions differed from the L-749 only through having a reinforced floor to handle cargo, and a large aft loading door. Although originally intended for cargo transport duties, they were usually fitted out with 44-seat passenger transport interiors. The aircraft also consisted of a five-man crew with four relief crew members on standby. All C-121As were assigned to the Atlantic division of the Military Air Transport Service (MATS). The aircraft would later see service in the Berlin Airlift. Dwight Eisenhower and General Douglas MacArthur both used the C-121A as their personal VIP transports. In 1950, six of the C-121A Constellations were modified as VIP transports and redesignated VC-121A. The last C-121As were retired in 1968.