6. The B-52s became conventional bombers over Vietnam in 1965
Following the 1964 Gulf of Tonkin incident the United States began to ramp up its combat involvement in the War in Vietnam. Approximately 74 Stratofortress bombers received modifications to carry conventional bombs. In March, 1965, the United States initiated Operation Rolling Thunder. B-52 involvement in the sustained aerial bombing of targets in Vietnam began in June. On June 18, 1965, 30 B-52s took off from Anderson Air Force Base in Guam, bound for a target zone said to be a Viet Cong concentration north of Saigon. While maneuvering at a refueling rendezvous point, two of the bombers collided in mid-air. Eight crewmen were killed and both bombers lost. Twenty-seven bombers struck the target area, though post-strike analysis revealed that nearly half of the bombs missed the target, which had already been abandoned by the Viet Cong.
In Vietnam the B-52 changed from a high-altitude strategic bomber to a lower altitude conventional strike weapon. Missions out of Guam typically lasted between ten and twelve hours, required refueling, and brought the bomber under anti-aircraft fire from both missiles and guns for the first time. Missions were later added out of Thailand. In late 1965, during the Battle of Ia Drang, B-52s flew close air support missions for the first time. ARVN and American troops attempted to lure North Vietnamese forces into open areas where the B-52s could deliver their massive bomb loads on the enemy. Although several of the heavy bombers were damaged by enemy fire, and several were lost to accidents, not until 1972 was a B-52 shot down in action. During the Vietnam War, B-52 tail gunners were credited with shooting down two enemy MiG 21 aircraft.