12 May 1965 – Operation Rolling Thunder was the codename for an American bombing campaign whereby U.S. military aircraft attacked targets throughout North Vietnam from March 1965 to October 1968. Before Operation Rolling Thunder started the North Vietnamese knew it was coming.
On 12 May 1965, President Johnson halted the bombing of North Vietnam under Operation Rolling Thunder in an attempt to induce the North Vietnamese to negotiate a peace agreement. North Vietnam instead said the bombing halt was only “an effort to camouflage American intensification of the war”. (1)
About 643,000 tons of bombs were dropped on North Vietnam from 1965 to 1968, and nearly 900 U.S. aircraft were lost during Operation Rolling Thunder. The operation continued, with occasional suspensions, until President Johnson, under increasing domestic political pressure, halted it on October 31, 1968.
Source: (1) Wikipedia, History.net