U-Tapao based B-52s flew in support of US Marines in the Battle of Khe Sanh in early-1968. Under "Operation Niagara" waves of six B-52s, attacking every three hours, dropped bombs as close as from the perimeter of the outpost. A total of 2,548 B-52 sorties were flown in support of the defense of Khe Sanh, dropping a total of 54,129 tonnes (59,542 tons) of bombs. U-Tapao based B-52s also bombed the southernmost part of North Vietnam near the Vietnamese Demilitarized Zone.