Marine Division until mid-February and the ROK 2nd Division thereafter to destroy the unit in the Pohang-Andong-Yongdok area, the division had maintained a formal organization of a headquarters and three regiments and with a surviving strength of about two thousand had managed by the opening of Operation Ripper to slip north through the Taebaek Mountains to the Irwol Mountain region, northeast of Andong. Easily withstanding further efforts of the ROK 2nd Division to eliminate it, the division by 13 March reached the Chungbong Mountain area, about miles south of Gangneung. As the KPA unit approached the ROK I Corps' rear, General Kim sent two regiments of the ROK 9th Division and a battalion of the Capital Division south to intercept it. The two forces clashed briefly in the Chungbong heights on the morning of the 13th to open what would become a cat-and-mouse affair lasting ten days. Advance to the Buffalo Line During the evening of the 13th General Ridgway ordered the next phase of the advance to begin the following morning. In the west, the 25th Infantry Division was to advance toward a segment of the Buffalo Line bulging above the Seoul-Chunchron road in a zone confined to the west side of the Pukhan River. In the main attack, IX Corps was to make its major effort in the right half of the Corps' zone, sending the 1st Cavalry and 1st Marine Divisions to clear Hongcheon and then to occupy the Buffalo Line above town to block Route 29 leading northwest to Chuncheon and Route 24 running through the Hongcheon River valley to the northeast. Only short advances were required in the western half of the IX Corps' zone, by the 24th Division at the left in conjunction with the I Corps advance and by the ROK 6th Division at the right to protect the flank of the forces attacking Hongcheon. To the east, X Corps and ROK III Corps were to continue toward the Idaho Line while, on the flank, ROK I Corps had only to maintain its forward positions in the coastal slopes while other Corps' forces concentrated on eliminating the KPA 10th Division. Against the continued advance, according to estimates prepared by Eighth Army intelligence as the initial assault concluded, the PVA delaying forces backing away from the 25th Infantry Division and the four divisions of IX Corps were expected to join their parent units in