 Phase III of the offensive began on 17 August and involved attacks in I , II , and III Corps . Significantly , during this series of actions only North Vietnamese forces participated . The main offensive was preceded by attacks on the border towns of Tây Ninh , An Lộc , and Loc Ninh , which were initiated in order to draw defensive forces from the cities . A thrust against Da Nang was preempted by the U.S. Marines on 16 August . Continuing their border @-@ clearing operations , three North Vietnamese regiments asserted heavy pressure on the U.S. Special Forces camp at Bu Prang , in Quang Duc Province , five kilometers from the Cambodian border . The fighting lasted for two days before the North Vietnamese broke it off ; the combat resulted in the deaths of 776 North Vietnamese , 114 South Vietnamese , and two Americans . 
