December 1970, with about 20 Batcats on hand at any time. The wing activated in December 1970 and the 554th RS relocated to Nakhon 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 USA. The final Batcat mission was in December 1971. The last remaining administrative and support personnel returned to Otis AFB in January 1972. Variants USN variants WV-1. 2 prototypes, L-749A Constellation, designated PO-1W before 1952 EC-121K (WV-2). Main USN variant, designated PO-2W before 1952; 244 ordered, 142 produced (the rest to USAF). JC-121K. One modified EC-121K used as a US Army avionics testbed NC-121K. Unknown number modified as special mission aircraft YEC-121K. One modified avionics testbed EC-121L (WV-2E). One modified WV-2, testbed for rotating radar dome with an AN/APS-70 radar EC-121M (WV-2Q). ELINT collection variant, 13 modified WV-2 WC-121N (WV-3. Weather reconnaissance variant, 8 modified WV-2 EC-121P. Unknown number modified from EC-121K as anti-submarine variant JEC-121P. 3 EC-121P used by the USAF USAF variants RC-121C: 10 produced, initial USAF variant JC-121C: 2 converted from C-121C and 1 TC-121C as avionics testbeds TC-121C: 9 RC-121C modified before 1962 as crew trainers EC-121D: 73 produced 1953–55 as main USAF variant and 1 converted from C-121C, originally designated RC-121D EC-121D Quick Look: 1 testbed for QRC-248 IFF transponder interrogator EC-121H: 42 USAF upgrades in 1962, 35x EC-121D and 7x WV-2s transferred from the Navy EC-121J: 2 USAF EC-121D modified with upgraded electronics EC-121M Rivet Top: 1 EC-121D testbed for Rivet Gym cryptologic linguist electronics suite, originally designated EC-121K EC-121Q: 4 EC-121D modified with upgraded electronics for USAF Gold Digger missions EC-121R: 30 EC-121K / EC-121P transferred to USAF in 1966–1967 and converted to Batcat sensor signal processor EC-121S: 5 converted for Pennsylvania Air National Guard from USAF C-121 transports EC-121T: Final USAF variant. A total of 22 T's were converted from 15x EC-121D and 7x EC-121H. XW2V-1: Proposed naval development with new features such as 4 Allison T56-A8 turboprop engines, L-1649A Starliner wings and Bomarc missiles for defense. None built; was designated L-084 due to the large differences from its predecessors. Operators USAF Active duty 551st AEWCW – Otis AFB, Massachusetts 960th AEWCS 961st AEWCS 962d AEWCS 552d AEWCW – McClellan AFB, California 963d AEWCS 964th AEWCS 965th AEWCS 553d RW – Korat RTAFB, Thailand 553d RS 554th RS 966th