Lockheed Constellation EC-121D

The Air Force began receiving its Warning Stars in October 1953, through diversions from Navy contracts, all of them derived from the L-1049 Super Constellation. Alongside ten RC-121Cs that ended up as trainers came 74 EC-121Ds: 73 newly built between 1953 and 1955 and one converted from a C-121C. They were first designated RC-121D; airframe 52-3418, for instance, was delivered in October 1954 as an RC-121D and became an EC-121D in 1962.

The layout matched the Navy's WV-2: an AN/APS-45 height-finder in the dorsal radome and an AN/APS-20 search radar in the ventral one, later replaced by the AN/APS-103 and AN/APS-95, though not at the same time. The usual crew was 18: six officers (two pilots, two navigators and two weapons controllers) and twelve enlisted men, among them two flight engineers, a radio operator, two crew chiefs, five radar operators and two radar technicians.

Until Vietnam, the mission was to complement the early warning coverage of the Pacific and Atlantic barriers. EC-121Ds flew orbits about 480 km off the continental coast, overlapping those of the land-based radars, in what were called 'contiguous barriers'. In the east, the 551st Airborne Early Warning and Control Wing at Otis, Massachusetts, operational from 21 December 1954, started with EC-121Cs and moved on to the EC-121D and then the EC-121H. Its Pacific counterpart, the 552d at McClellan, California, became operational on 1 July 1955. After the Cuban Missile Crisis of 1962 it also controlled the 966th squadron at McCoy, Florida, which watched Cuban airspace and tracked U-2 flights on Gold Digger missions. That experience over Cuba produced the skills later put to use in Asia.

When Rolling Thunder began, North Vietnamese radar could see almost any American strike aircraft above about 1,500 m, while the Crown radar ships and the Nakhon Phanom site left gaps. At the request of Seventh Air Force the Big Eye Task Force was formed: five EC-121Ds and a hundred support personnel of the 552d deployed to Tainan, Taiwan, and four aircraft went on to Tan Son Nhut, near Saigon.

The EC-121D had been designed to detect aircraft over the sea, and ground clutter spoiled its picture over land. The crews applied a technique learned off Cuba: flying 15 to 91 m above the water, they bounced the signal of the ventral APS-95 off the surface and detected aircraft at medium altitude out to 240 km. They worked in pairs, one in the Alpha orbit, a wave-top racetrack about 48 km offshore, the other in the Bravo orbit at about 3,000 m and farther out as a spare. The practical range of some 160 km covered Hanoi and the MiG base at Phúc Yên, but most contacts lay beyond the 110 km reach of the APS-45 height-finder, and the system could neither direct an intercept nor tell which flight was under attack.

Missions began on 21 April 1965 under the callsigns Ethan Alpha and Ethan Bravo. After refuelling at Da Nang, the aircraft ran in at wave-top height and spent five hours on station, with useless air conditioning, the heat of the electronics and the threat of MiGs; F-104 Starfighters escorted them, and if the escort failed to show, the mission was cancelled. On 10 July 1965, in the first airborne-controlled interception, an EC-121 warned two F-4Cs that went on to shoot down two MiG-17s.

In May 1966, after a Chinese protest over an F-105 that had chased a MiG into its territory, the task force also had to watch the border, and a third orbit over Laos, Ethan Charlie, was opened, flown regularly from 24 August and daily from 13 October 1966. In February 1967 the threat of Viet Cong attacks moved the group to Thailand; in March it was renamed College Eye and passed through Ubon and Udon before settling at Korat in October.

The EC-121Ds also controlled escorts and MiGCAPs, relayed radio traffic to the Da Nang centre, guided search and rescue and helped fighters locate tankers. The leap came with the QRC-248 interrogator, developed to follow Cuban MiGs: the Quick Look testbed confirmed in January 1967 that the North Vietnamese used the same transponder, and by May every College Eye carried it, with low-level detection beyond 282 km. Active interrogation was finally authorised on 6 October, and on 4 December the Alpha orbit was dropped until July 1972.

On 24 October 1967, over the Gulf of Tonkin, EC-121D 53-0555, nicknamed 'Triple Nickel' for its serial, guided an American fighter by radar into position to destroy a MiG-21: the first time a weapons controller aboard an airborne radar aircraft had directed a successful attack on an enemy aircraft. It was retired to the Air Force Museum in 1971.

From 1 March 1968 the callsigns became Ethan 01 to 04, and on 19 April Ethan 03 began directing C-130 flareships and A-26s over the Ho Chi Minh Trail. In July the force was cut to four EC-121Ds and the Rivet Top aircraft, and in October 1968 it became Detachment 1 of the 552d; deployments stopped in June 1970. That November, two EC-121Ds with the SEAOR-62 electronics, not yet operational as EC-121Ts, supported the Son Tay prisoner rescue attempt as Frog 01 and 02. When the detachment returned to Korat as Disco in late 1971, it flew EC-121Ts, largely converted from EC-121Ds. Between 1965 and 1973 the EC-121s flew 13,921 combat missions and more than 98,000 accident-free hours, helped shoot down 25 MiGs and rescue 80 airmen, and no Big Eye, College Eye or Disco aircraft was lost.

Of the 74 EC-121s, 42 were upgraded to EC-121H from 1962, and in 1969 fifteen of the remaining EC-121Ds joined seven EC-121Hs in becoming EC-121Ts. Five EC-121Ds were turned into psychological warfare broadcasters, forerunners of the EC-130 Commando Solo; two became EC-121Js and four EC-121Qs for Gold Digger missions. The 551st was inactivated in 1969 and the 552d, cut to a one-squadron group in 1974, in April 1976. 'Triple Nickel' is displayed restored indoors at Dayton, and 52-3418, later converted to an EC-121T, at the Combat Air Museum in Topeka.