On this day in 1972, the U.S. Air Force started using the B-52 Bombers on northern Vietnam at the peak of the Vietnam and Cold Wars. The Bombers struck within the vicinity of Vihn, approximately 145 Miles from the Demilitarized Zone. It was then later publicly acknowledged that the target priority was the SAM-2 Missile Sites, which made flying over northern Vietnam increasingly more hazardous. U.S. Officials said that Hanoi’s defense system was “one of the most sophisticated air defenses in the history of air warfare.” The defenses were made up of advanced radar and highly accurate lethal air-defense missiles.