The USAF received 10 RC-121C and 74 EC-121D Warning Stars also based on the L-1049 beginning with diversions from the Navy contracts in October 1953. The 10 RC-121Cs became trainers, designated TC-121C. Between 1966 and 1969, 30 retired USN EC-121s were transferred to USAF and converted in EC-121Rs as "sensor-monitoring" aircraft. Of the 74 EC-121s, 42 were converted to the EC-121H upgrade beginning in 1962 and in 1969, 15 of the remaining EC-121Ds and 7 of the EC-121Hs were further upgraded into the final operational variant, the EC-121T, serving as an AWACS prototype in Southeast Asia in 1972. Five EC-121Ds were modified to be broadcasting aircraft for psychological warfare operations, the predecessors of the EC-130 Commando Solo.