Operation Ripper, also known as the Fourth Battle of Seoul, was a United Nations military operation conceived by the commander US Eighth Army, General Matthew Ridgway, during the Korean War. The operation was intended to destroy as much as possible of the Chinese communist People's Volunteer Army and North Korean military around Seoul and the towns of Hongch'on, 50 miles (80 km) east of Seoul, and Ch'unch'on, 15 miles (24 km) further south. The operation also aimed to bring UN troops to the 38th parallel. It followed upon the heels of Operation Killer, an eight day UN offensive that concluded February 28, to push Communist forces north of the Han River. The operation was launched on March 6, 1951 with the US I Corps and IX Corps on the west near Seoul and Hoengsong and US X Corps and ROK III Corps in the east, to reach "Line Idaho", an arc with its apex just south of the 38th Parallel in South Korea.
Operation Ripper was preceded by the largest artillery bombardment of the Korean War. On the middle, the U.S. 25th Infantry Division quickly crossed the Han and established a bridgehead. Further to the east, IX Corps reached its first phase line on 11 March. Three days later the advance proceeded to the next phase line. During the night of March 14–15, elements of the South Korean 1st Infantry Division and the US 3rd Infantry Division liberated Seoul, marking the fourth and last time the capital would have changed hands since June 1950. The Communist forces were compelled to abandon it when the UN approach to the east of the city threatened them with encirclement.
Following the recapture of Seoul the communist forces retreated northward, conducting skillful delaying actions that utilized the rugged, muddy terrain to maximum advantage, particularly in the mountainous US X Corps sector. Despite such obstacles, Operation Ripper pressed on throughout March. In the mountainous central region, the US IX and US X Corps pushed forward methodically, the IX Corps against light opposition and the X Corps against staunch enemy defenses. Hongch'on was taken on the 15th and Ch'unch'on secured on the 22nd. The capture of Ch'unch'on was the last major ground objective of Operation Ripper.
UN forces had advanced north an average of 30 miles (48 km) from their start lines. However, while the US Eighth Army had occupied their principal geographic objectives, the goal of destroying Chinese forces and equipment had again proved elusive. More often than not, the communist forces withdrew before they could receive extensive damage. Ch'unch'on, a major communist supply hub, was empty by the time UN forces finally occupied it. As the U.N. troops ground forward, they were constantly descending sharp slopes or ascending steep heights to attack enemy positions that were sometimes above the clouds. By the end of March, US forces reached the 38th parallel.
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