water and detect aircraft at medium altitudes out to 150 miles. Operating in pairs, one Big Eye EC-121 flew a 50-mile race track pattern approximately 30 miles offshore (Alpha orbit), with the orbit's center at . The second one flew a track at 10,000 feet (Bravo orbit) farther from the coast, acting as a spare for the Alpha EC-121. This provided a practical detection range of 100 miles, enough to cover the Hanoi urban area and the main MiG base at Phúc Yên. A major disadvantage of this arrangement, however, was that most MiG contacts were beyond the 70-mile range of the Big Eye's APS-45 Height Finder radar, so that they were unable to provide this data to USAF strike forces. Furthermore, technical shortcomings in the EC-121D's systems precluded either controlling a fighter intercept or identifying a specific flight under attack. The missions from Tan Son Nhut AB began 21 April 1965, using callsigns Ethan Alpha and Ethan Bravo, which became standard. After refueling at Danang Air Base, Ethan Alpha made a wave-top approach to its orbit station, where it remained for 5 hours. Because of the threat of MiG interception, EC-121s were protected by a Lockheed F-104 Starfighter MiGCAP. If, for any reason, the MiGCAP could not rendezvous, the EC-121s cancelled their mission. Airco systems aboard the EC-121 were virtually useless in this profile, and the heat produced by the electronics, combined with the threat of being shot down, made Alpha orbit missions in particular very stressful. On 10 July 1965, in its first airborne-controlled interception, an EC-121 provided warning to a pair of USAF F-4C fighters, resulting in the shooting down of two MiG-17s. The Big Eye Task Force remained at Tan Son Nhut until February 1967, when the threat of Viet Cong ground attacks prompted a move to Thailand. College Eye In March 1967, Big Eye was renamed College Eye Task Force (CETF) and relocated at Ubon Royal Thai Air Force Base. Because of the complexity of the aircraft and its systems along with the large support group it required, CETF was not welcome at the relatively small Thai bases. It moved to Udon RTAFB in July and to its final station at Korat RTAFB in October 1967. Seven of 26 EC-121s deployed from Otis AFB and arrived at Korat, on the 19th. From April 1965 to early 1966 and beginning again in late 1967, the EC-121Ds