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 2 MiG-17s.