The Lockheed Martin EC-121 Warning Star was a military variant of the Lockheed Super Constellation, designed to become an airborne early warning and surveillance aircaft. The EC-121 was used by both the United States Air Force and the United States Navy. The task of the aircraft was to supplement the Distant Early Warning Line (the DEW, was a system of radar stations, based in the northern region of Canada, other stations were based along the North Coast and Aleutian Islands of Alaska, addiitional were at the Faroe Islands, Greenland, and Iceland, with the task to detect Soviet bomber fleets), the EC-121 was used as a signals intelligence (SIGINT) aircraft as well.
The first time the US Navy studied the use of Constellation aircraft as airborne early warning aircraft was in 1949. The first PO-1W designated airborne early warning Constellation was equipped with long range radars, which were mounted on the top and below the fuselage was first flown on 9th June 1949.
The EC-121 Warning Star was first introduced in the year 1954 and was in service until 1978, only a single Electronic Warfare variant remained in active service with the United States Navy, it was retired in 1982.