During the Vietnam War some 30 EC-121s were modified from U.S. Navy WV-2 and WV-3 early warning Constellations for use with ground sensors to detect enemy troop movements along the Ho Chi Minh Trail, and 25 were deployed to Southeast Asia, at Korat Royal Thai Air Force Base, as a part of Operation Igloo White. The resulting EC-121R configuration was nicknamed the Batcat. Two Batcats were lost during the war, with the loss of 22 crewmen, one in a takeoff accident during a thunderstorm on 25 April 1969, the other on 6 September 1969, in a landing accident. Four Thai civilians on the ground were also killed in the second crash.
Batcat EC-121s were camouflaged in the standard three-color Southeast Asia scheme while the College Eye/Disco early warning aircraft were not. BatCat missions were 18 hours in length, with eight hours on station at one of 11 color-coded orbits used during their five-year history, three of which were over South Vietnam, six over Laos, one over Cambodia, and one over the Gulf of Tonkin.
EC-121Rs were operated by the 553rd and 554th Reconnaissance Squadrons of the 553rd Reconnaissance Wing, between 19 October 1967 and 15 December 1970, with approximately 20 Batcats on hand at any one time. The Wing was inactivated 15 December 1970, and the 554th RS relocated toNakhon Phanom RTAFB to fly QU-22 sensor monitors nicknamed "Baby Bats". Initially with 11 aircraft, the 553rd RS continued operations for another year, gradually returning aircraft and crews to the United States. The final Batcat mission was flown 5 December 1971. The last remaining administrative and support personnel returned to Otis Air Force Base, Massachusetts, in January 1972.
