Howard Hughes was one of the driving forces behind the design of the Lockheed Constellation commercial transport. During WWII, the USAAF purchased 22 early model Constellations which were designated as C-69s. At the end of the war, the USAAF decided to standardize on the Douglas C-54 as its four-engined transport of choice, and promptly declared most of the C-69s as surplus. Production of the basic design was turned over to the civil market, which lead to the famous Constellation series of airliners.
The C-121A was the military variation of commercial Model 749 Constellation. Between 1948 and 1955 the USAF ordered 150 C-121As for use as cargo/passenger carriers, executive transports, and airborne early warning aircraft. As a troop carrier, they could carry a maximum of 44 passengers.
Fifty-five percent of the Super Constellations built by Lockheed were delivered to the U.S. Navy and Air Force. A majority of the aircraft were used for electronic reconnaissance and airborne early warning. In the mid-1960s, the Air Force sent the first EC-121 "Warning Star" to Southeast Asia to maintain radar surveillance over North Vietnam and then later to warn of MiG attacks and alert American pilots who were straying over Chinese territory.
Most C-121As were later converted into the VC-121A VIP transport configuration for use by top brass officials such as Generals MacArthur and Eisenhower. The lone VC-121E Constellation (#53-7885) was named "Columbine III" and was used throughout the Eisenhower Administration as Air Force One.
All C-121As were phased out of service by 1968.