The Eighth Army ordered a complete withdrawal to the Imjin River, south of the 38th Parallel. On 1 January 1951, PVA troops attacked the Eighth Army's defensive line at the Imjin River, forcing them back and allowing the PVA to capture Seoul. The PVA offensive was finally blunted by the 2nd Infantry Division on 20 January at Wonju. Following the establishment of defenses south of Seoul, General Matthew B. Ridgway ordered US I, IX and X Corps to conduct a general counteroffensive against the PVA/KPA, Operation Thunderbolt. Taking up the offensive in a two-prong attack in February 1951, the Division repulsed a powerful PVA counter-offensive in the epic battles of Chipyong-ni and Wonju. The UN front was saved and the general offensive continued.