The Lockheed EC-121 Warning Star was a US Air Force/US Navy 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-121's were also used for intelligence gathering (SIGINT). It was introduced in 1955 and retired from service in 1978, although a single specially-modified EW aircraft remained in service with the U.S. Navy until 1982. The US Navy versions when initially procured were designated WV-2 and WV-3. Warning Stars of the U.S. Air Force served during the Vietnam War as both electronic sensor monitors and as a forerunner to the E-3 Sentry AWACS. U.S. Air Force aircrews adopted the civil nickname, "Connie" (diminutive of Constellation) as reference.