18 JUN--This Day in US Military History

1965 – For the first time, 28 B-52s fly-bomb a Viet Cong concentration in a heavily forested area of Binh Duong Province northwest of Saigon.

Such flights, under the aegis of the Strategic Air Command (SAC), became known as Operation Arc Light. The B-52s that took part in the Arc Light missions had been deployed to Andersen Air Force Base in Guam and more bombers were later deployed to bases in Okinawa and U-Tapao, Thailand. In addition to supporting ground tactical operations, B-52s were used to interdict enemy supply lines in Vietnam, Cambodia, and Laos, and later to strike targets in North Vietnam.
Releasing their bombs from 30,000 feet, the B-52s could neither be seen nor heard from the ground as they inflicted awesome damage. B-52s were instrumental in breaking up enemy concentrations besieging Khe Sanh in 1968 and An Loc in 1972. Between June 1965 and August 1973, 126,615 B-52 sorties were flown over Southeast Asia. During those operations, the Air Force lost 29 B-52s: 17 from hostile fire over North Vietnam and 12 from operational causes.

https://thisdayinusmilhist.wordpress.com/2005/06/19/june-18/