In the late 1940s Lockheed investigated the idea of adapting the Constellation airliner for patrol and airborne early warning duties. The US Navy tacitly recognized the Constellation's potential as an AEW platform, and in late 1948 it ordered two L-749s with AEW radar (BuNos 124437/124438) designated PO-1W, and the first of the two PO-1Ws flew on June 9, 1949. The PO-1W carried large, long-range search radars in massive radomes above and below the fuselage, and the huge amount of side area possessed by the radomes meant that the PO-1W had bigger vertical stabilizers than those of the L-749. Impressed by flight tests of the PO-1W, in the summer of 1950 Lockheed put forward an AEW version of the L-1049 Super Constellation, the L-1049A, and in 1951 the Navy ordered six L-1049As with the designation PO-2W (BuNos 126512/126513, 128323/128326). When the Navy's Bureau of Aeronautics introduced the W-for-Airborne Early Warning aircraft mission category in 1951, the PO-1W and PO-2W were redesignated WV-1 and WV-2 respectively. Deliveries of the WV-2 to Navy electronic warfare units began in 1953, with 136 more WV-2s (BuNos 131387/131392, 135746/135761, 137887/137890, 141289/141333, 143184/143225, 143226/143230, and 145924/145941*) completed. Although airborne early warning versions of the Super Constellation weren't given an official name, Lockheed dubbed them the Warning Star.
*Twenty-two more WV-2s (BuNos 131393/131399 and 145942/145956) were on the US Navy's order books in addition to the first six WV-2s initially designated PO-2W and the other 136 completed WV-2s, but they were cancelled without being built.
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| Left: The first RC-121C (serial number 51-3836) in flight, 1955 Right: An EC-121D (serial number 53-0128) in flight with two F-104s, 1958 |
Even before the first WV-2s began flying, the US Air Force was shopping for an airborne early warning aircraft of its own, and in 1951 it procured ten L-1049Bs originally ordered by the Navy, designating them RC-121C and assigning serial numbers 51-3836/3845 to these aircraft. The RC-121C first flew in 1952 and deliveries to the USAF began in January 1953. A Navy order for 72 WV-2s was also diverted to the Air Force and given the designation RC-121D. The first flight of the RC-121D took place in May 1954 and the deliveries started the following month, with operational deployment of the RC-121D commencing on December 21. Serial numbers 52-3411/3425, 53-533/556, 53-3398/3403, 54-2304/2308 and 55-118/139 were allocated to the RC-121Ds, and one C-121C (serial number 54-183) was converted to an RC-121D. The RC-121C and RC-121D were redesignated EC-121C and EC-121D respectively in 1955. Like the WV-2, the EC-121C and EC-121D were equipped with dorsal and ventral radomes to house the AN/APS-45 height finder and AN/APS-20 search radar respectively, and they could carry a crew of 18 (two pilots, two navigators, two weapons controllers, two flight engineers, one radio operator, two crew chiefs, five radar operators, and two radar technicians). However, in contrast to the EC-121C, the EC-121D had the wingtip tanks of the WV-2 and utilized select equipment changes. The EC-121C and EC-121D were tasked with providing complementary early warning radar coverage to the North Pacific and North Atlantic barriers by flying orbits 300 miles (480 km) offshore from the continental US in what were termed "contiguous barriers", and coverage orbits overlapped those of land-based early warning radars. Three R7V-1s (BuNos 128436, 128438/128439, 131638) acquired by the US Air Force in 1954 were designated TC-121G and reserialled 54-4050/4052 and 54-4058 after being modified to traincrews to fly the EC-121C and EC-121D (serial number 54-4051 would later be converted to a VIP transport and redesignated VC-121G). Two RC/EC-121Cs were lost in accidents, one ditching in San Pablo Bay near San Francisco on November 21, 1953, and another crashing during a flight in rainy weather in Marysville, California, on March 22, 1961, and after the latter accident the remaining EC-121Cs were converted to AEW crew training aircraft and redesignated TC-121C. In 1962, 42 EC-121D airframes and seven ex-USN WV-2s (the latter reserialled 55-5262/55-5268) were redesignated EC-121H after being modified with the SAGE (Semi-Automatic Ground Environment) electronic suite for the AEW role and upgraded new dorsal and ventral radomes housing the APS-103 and APS-95 search radars respectively. The designation EC-121J was assigned to two EC-121Ds (serial numbers 52-3416 and 55-137) modified with additional electronic equipment in the early 1960s, and the US Air Force also acquired three examples of the EC-121P anti-submarine variant of the EC-121K for avionics testing, referring to them as the JEC-121P.
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| Left: EC-121Ds (serial number 53-3400 in the foreground) at Khorat Royal Thai Air Force Base, Thailand, in 1968. (Courtesy of US Air Force) Right: An EC-121R on a surveillance mission over Southeast Asia on January 15, 1969. (Courtesy of US Air Force) |
After the October 1962 missile crisis, four EC-121Ds of the 966th Airborne Early Warning and Control Squadron based at McRoy AFB near Orlando Florida, were fitted with upgraded electronics and given the designation EC-121Q, and they monitored activities in Cuban airspace and tracked U-2 overflights of Cuba as part of Operation Gold Digger. After the start of Operation Rolling Thunder in March 1965, EC-121s began providing radar early warning and limited airborne control of USAF fighter squadrons fighting North Vietnamese MiGs, and the Big Eye Task Force stationed at the Tan Son Nhut Air Base in Saigon, South Vietnam, was set by the USAF's 552nd Airborne Early Warning and Control Wing to provide support for EC-121Ds making orbits around the Gulf of Tonkin. The first time that the EC-121 successfully used airborne-control interception in the Vietnam War occurred on July 10, 1965, when it provided warning to a pair of F-4C Phantom II jet fighters, which led the F-4Cs to shoot down two North Vietnamese MiG-17s. The Big Eye Task Force relocated to Thailand in 1967 due to the threat of attacks on Tan Son Nhut AB by the Viet Cong and changed its name to the College Eye Task Force, and in April of that year all EC-121s operating with the College Eye Task Force were fitted with QRC-248 IFF transponder interrogators. Back in January 1967, as part of Project Quick Look, the NC-121D (originally designated GRC-121D), which had been built as a WV-2 with BuNo 143226 before being transferred to the US Air Force and given the new serial number 56-6956, was used as a testbed for the QRC-248 system. Beginning in July 1967, the Air Force EC-121s fitted with the QRC-248 system orbited airspace over Laos to provide airborne control of US military aircraft going after Viet Cong activities along the Ho Chi Minh trail. In August 1967, one WV-2 (EC-121K after 1962) originally operated by the Navy with BuNo 143184 and designated EC-121M (not to be confused with the EC-121M ELINT version of the EC-121K) after being acquired by the US Air Force began operational testing of the top-secret Rivet Gym electronics suite (consisting of voice communications intercept stations manned by Vietnamese-speaking intelligence specialists) under Project Rivet Top. After being moved to Korat Royal Thai Air Force Base along with the College Eye Task Force in October 1967, the Rivet Top prototype undertook AEW operations over the Gulf of Tonkin beginning in April 1968, and the EC-121s assigned to the College Eye Task Force were fitted with the Rivet Gym electronics suite the following month. The EC-121R (nicknamed "Batcat") was an EC-121 iteration with ground sensors to detect enemy activities along the Ho Chi Minh trail, and 28 EC-121K/P aircraft and two examples of the WC-121N (WV-3 before 1962) weather reconnaissance aircraft were modified to EC-121Rs after being acquired by the US Air Force in 1966-1967 and assigned serial numbers 67-21471/21500. Painted in the tree-color Southeast Asia camouflage scheme and lacking radomes, the EC-121Rs were deployed to Thailand as part of Operation Igloo White and undertook eavesdropping activities over the Ho Chi Minh trail from October 1967 to December 1971.
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Left: An EC-121T (serial number 53-548) (built as an RC/EC-121D) on display at the Yanks Air Museum in Chino, California, photographed by me on July 27, 2022. |
The Warning Star that I've seen at the Yanks Air Museum is an example of the last USAF variant of the EC-121, the EC-121T. In the summer of 1970, 22 EC-121D/H aircraft and one EC-121J were fitted with improved electronic systems, namely a digital data receiver, and they were redesignated EC-121T. Many of the EC-121Ts had the dorsal radome and radar removed, but others retained it. On November 12, EC-121Ts began arriving in Thailand from McClellan AFB in California to provide an integrated tactical data display with real-time inputs in support of Operation Kingpin, a mission to rescue US prisoners of war presumably held at the Son Tay prison in Hanoi. The EC-121T would provide radar early warning to jet fighters during the last years of the Vietnam War, especially during Operations Linebacker and Linebacker II, and EC-121Ts with callsign Disco provided radar support while orbiting Laotian airspace and the Gulf of Tonkin in 1971-1972. The last Disco EC-121T mission was flown on August 15, 1973, and the EC-121s stationed at Khorat RTAFB were withdrawn from Southeast Asia on June 1, 1974. The EC-121T was retired from service on March 28, 1975, while the TC-121G would follow suit in June.
In late 1975, the US Air Force began withdrawing the EC-121 from operational service as it prepared to take deliveries of the new jet-powered Boeing E-3 Sentry. All remaining EC-121s were transferred to the US Air Force Reserve's 79th AEWCS at Homestead AFB in Miami-Dade County, Florida, in early 1976, and they continued monitoring Soviet military activities in Cuba until October 1978, when they were retired, ending the quarter-century career of the USAF's Warning Stars.
References:
Breffort, D., 2006. Lockheed Constellation: From Excalibur to Starliner, Civilian and Military Variants. Paris, France: Histoire and Collections.
Michel, M.L., 1997. Clashes: Air Combat Over North Vietnam 1965–1972. Annapolis, MD: Naval Institute Press.
Winchester, J., 2001. Lockheed Constellation. St. Paul, MN: MBI Publishing.
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