To avoid the possible entrance of Chinese or Soviet forces into the conflict, Washington tightly controlled these bombing operations. Limitations imposed included no bombing in the "sanctuaries" around Hanoi (the capital of North Vietnam), Haiphong (North Vietnam's main port), and a buffer zone along the Chinese border. Moreover, many types of targets remained off limits early in the campaign, including enemy airfields, surface-to-air missile (SAM) sites and petroleum facilities.
In July 1965, the US had its first SAM loss in Southeast Asia when a Soviet-built SA-2 SAM shot down a USAF F-4 Phantom. The U.S. began flying IRON HAND missions against the rapidly expanding missile sites, which the North Vietnamese concentrated in the Hanoi-Haiphong sanctuary. The Hanoi-Haiphong SAM sites were initially placed off limits for fear of killing Soviet or Chinese technicians working there. By the end of the year, U.S. reconnaissance aircraft had located 56 multiple-launcher SAM sites.
Planners hoped to use bombing halts to encourage Hanoi to discuss a political settlement. The first ROLLING THUNDER bombing halt lasted six days during May 1965. On Dec. 24, 1965, President Johnson declared another bombing halt that lasted until Jan. 30, 1966. Hanoi used these pauses to rebuild its strength, repair damage and send more troops and supplies to the battle zone. So, when ROLLING THUNDER missions resumed, U.S. aircrews not only had to attack new targets, but also those previously destroyed and repaired during the bombing halts.
In September 1966 North Vietnam sent up MiG-21 interceptors in force for the first time. They flew from five undamaged air bases not previously attacked because of U.S. policy. By the end of the year, ROLLING THUNDER had progressed northward, finally reaching the Hanoi area.
Early in 1967, Washington approved ROLLING THUNDER targets closer to Hanoi. By this time, North Vietnam fielded about 100 MiG fighters, and US aircraft losses mounted. Finally, in April U.S. aircrews received permission to attack four of the five MiG airfields. By the end of 1967, the U.S. aircrews downed 75 MiGs at a cost of 25 US aircraft in air-to-air combat.
On March 31, 1968, President Johnson ordered another bombing halt north of the 20th parallel, hoping once again to bring North Vietnam's leaders to the peace table. As before, North Vietnam continued to move troops into South Vietnam. With operations against North Vietnam halted, the US doubled its air operations south of the 20th parallel, concentrating on enemy troops and supplies crossing the DMZ.
After several months of discussion at Paris, on Oct. 31, 1968, Johnson ordered a complete halt to all air, naval, and artillery bombardment of North Vietnam, and the ROLLING THUNDER campaign came to an end.