Which Warning Star was called "Triple Nickel," and why is it historic?

Within the EC-121 Warning Star family, the early-warning aircraft derived from the Super Constellation, US Air Force aircraft 53-0555 earned the nickname "Triple Nickel" for the three fives in its serial number (53-555). It was an EC-121D assigned to College Eye, the radar aircraft deployment that monitored airspace during the Vietnam War.

That day, while operating over the Gulf of Tonkin, the Triple Nickel's crew picked up a North Vietnamese fighter, a MiG-21, on radar and guided a US fighter into attack position. The MiG-21 was shot down. It was the first time a weapons controller aboard a radar aircraft had successfully directed an attack against an enemy aircraft, a mission that decades later would become routine for AWACS.

The aircraft was retired in 1971 and transferred to the Air Force museum. Today it is displayed, fully restored and under cover, at the National Museum of the United States Air Force, at Wright-Patterson base near Dayton, Ohio, as a testament to the early days of airborne air control.

The EC-121 family kept evolving afterward: in 1969 some EC-121D aircraft were upgraded to EC-121T, the last operational variant, which served in 1972 as an AWACS prototype in Southeast Asia.

The Triple Nickel was not an isolated case. The Air Force eventually had 74 EC-121 aircraft, of which 42 were converted into EC-121H from 1962 onward, while others carried out very different missions in the same conflict: in 1966 Lockheed converted 30 Navy Super Constellations into EC-121R, intended to monitor sensors along the Ho Chi Minh trail.