An integral part of the Igloo White sensor system for detecting enemy activity on the Ho Chi Minh Trail was the EC-121R Bat Cat aircraft. Lockheed Air Services converted thirty surplus US Navy EC-121K and EC-121P aircraft to EC-121R configuration in 1966-1967. The 553rd RW was formed at Otis AFB, Massachusetts in February 1967 to operate the aircraft. The Wing deployed to Korat in October 1967 and was tasked with the collection of electronic intelligence information. Normally the aircraft orbited over South Vietnam, Laos or even North Vietnam for about eight hours while its seven-man combat information crew tuned into radio transmissions from air-dropped sensors. A variety of these sensors were used with names like Acoubuoy, Spikebuoy, Adsid and Acousid and they relayed acoustic and seismic information from the nearby movement of trucks and people on the Ho Chi Minh Trail. The information received from these sensors could be relayed to the Task Force Alpha centre at Nakhon Phanom or it could be analysed on board the EC-121Rs by its mission crew of radio and electronic specialists. The information thus received was used for the targeting of air strikes on sections of the Trail which were known to be active. By mid-1970 the number of EC-121Rs at Korat had been reduced from the original 27 to nine aircraft and the Wing was inactivated on 15 December 1970.