In April 1964, the division switched from "Air Mail" B-47 / KC-97 to "Reflex" B-52 / KC-135 alert forces, again with aircraft and crews furnished in deployed status from U.S. based SAC wings. In 1965, it became heavily involved in Arc Light and Young Tiger operations in the Far East and SE Asia (SEA). Strategic Air Command wings in the U.S. furnished the aircrews and aircraft for these operations. The first elements of the 3rd Air Division to enter combat in SEA were the tanker forces under Young Tiger. In June 1965, Arc Light B-52s struck suspected Viet Cong targets in South Vietnam, commencing the first SAC combat missions. B-52s began striking targets in North Vietnam on 11 April 1966; the initial attack against the Mu Gia Pass marked the largest single bomber raid since World War II. By late 1969, most Arc Light operations staged from U-Tapao Royal Thai Navy Airfield, Thailand, while others were mounted from Kadena Air Base, Okinawa and Andersen. Andersen AFB remained the primary base for SAC deployed forces from the U.S., however, and aircraft and crews were sent from Guam to Kadena and U Tapao for combat missions.