High Quality Content by WIKIPEDIA articles! The Lockheed EC-121 Warning Star was a United States Navy and United States Air Force airborne early warning radar surveillance aircraft. A military version of the Lockheed Constellation, it was designed to serve as an airborne early warning system to supplement the Distant Early Warning Line, using two large radomes, a vertical dome above and a horizontal one below the fuselage. EC-121s were also used for intelligence gathering (SIGINT).