The Warning Star is a US Air Force/US Navy airborne early warning radar surveillance aircraft manufactured by Lockheed, designed to serve as an airborne early warning system to supplement the Distant Early Warning Line.
The RC-121D is the designation of EC-121D before 1962. The USAF operated three wings of EC-121s between 1954 and 1978. Its primary mission until the Vietnam War was to provide complementary early warning radar coverage to the Pacific and Atlantic barriers by flying orbits 300 miles offshore of the continental United States. The initial deployment of EC-121Cs began with the 551st Airborne Early Warning and Control Wing based at Otis Air Force Base, Massachusetts. The EC-121 Warning Star became operational on December 21, 1954 and was subsequently upgraded to EC-121D and later EC-121H. The EC-121s were used extensively in support of Operation Rolling Thunder and Operation Linebacker/Linebacker II, to provide radar early warning and limited airborne control of USAF fighter forces engaging MiG interceptors. The EC-121s were designed to detect aircraft flying over water and ground clutter caused interference with their radar pictures.
The RC-121D has a typical flight crew of 6, with 11-25 radar crew. It has a maximum speed of 299 mph and a range of 4,250 mi.
An RC-121D is currently on display at the Chanute Air Museum in Rantoul, IL.