In 1968, US forces in Vietnam were faced with their biggest battles yet: On January 31,1968, Viet Cong and NVA forces violated the Tet cease-fire and launched the Tet Offensive all across South Vietnam. US Army and Marines plus ARVN units, fought 80,000 enemy in bloody battles as they attacked over 100 cities including every provincial capital, and Saigon itself. US and ARVN forces repelled the communists in weeks, after inflicting very heavy losses on VC/NVA forces.Simultaneously the NVA surrounded the US Marine base and airfield at Khe Sanh. NVA artillery, rockets, and mortar fire were placed on Khe Sanh with the intention of inflicting another Dien Bien Phu on the Americans. Instead President Johnson ordered "Operation Niagara", one of the heaviest air bombing campaigns in history, in order to destroy the enemy and keep the base in American hands.