 In late September heavy monsoon rains had swollen the Ben Hai River, forcing remnants of the PAVN 320th Division and independent regiments north across the river, but military intelligence indicated that some groups had been trapped in the south by the rising water.On 26 September Companies B, C, and D, 11th Infantry moved out from positions at C-2 and C-2 Bridge.In coordination with the ARVN 2nd and 3rd Battalions, 2nd Regiment, and the 3rd Marines, the companies moved to a position west of Con Thien and then attacked north across the southern boundary of the DMZ, toward the Dong Be Lao mountain complex.