The military version of the Lockheed L-1049 Super Constellation was used to serve as an airborne early warning system to supplement the Distant Early Warning Line, using 2 large radomes (a vertical dome above and a horizontal one below the fuselage). It replaced the TBM-3W used by the USN. Some EC-121s were also used for "Signal Intelligence" gathering (SIGINT). The EC-121 was introduced in 1954 and phased out in 1978, although a single specially modified EW aircraft remained in USN service until 1982.