A U.S. Air Force Lockheed EC-121K "Rivet Top" (s/n 57-143184) of the 552nd Airborne Early Warning & Control Wing, based at Korat Royal Thai Air Force Base, Thailand, in 1967-68. "Rivet Top" was a modification of a EC-121 into a Airborne Tactical Air Coordination Center, where intelligence collection and command and control functions were fused on a single airframe. For this a former U.S. Navy EC-121K (BuNo 143184) was modified. "Rivet Top" operators listened in on radio calls between MiG fighters and their ground controllers.