Airplane USAF/ USN Lockheed RC-121D Warning Star 19.25" Wood Mode Aircraft The Lockheed aircraft RC-121D, which was also called the Lockheed aircraft, was the United States Air Force and the United States Navy airborne early warning system that supplemented the Distant Early Warning Line. It came with two huge radomes, with one being horizontally located below the fuselage and the other, a vertical one, situated positioned on top of the aircraft. The aircraft was used for gathering intelligence (SIGINT). Introduced in 1984, the US Air Force and the US Navy used the Lockheed ECE-121 as an intelligence aircraft for more than 20 years, before it retired in 1978.