Operation Ripper, also known as the Fourth Battle of Seoul, was a United Nations (UN) military operation conceived by the US Eighth Army, General Matthew Ridgway, during the Korean War. The operation was intended to destroy as much as possible of the Chinese People's Volunteer Army (PVA) and Korean People's Army (KPA) forces around Seoul and the towns of Hongch'on, east of Seoul, and Chuncheon, further north. 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 PVA/KPA forces north of the Han River. The operation was launched on 6 March 1951 with US I Corps and IX Corps on the west near Seoul and Hoengsong and US X Corps and Republic of Korea Army (ROK) III Corps in the east, to reach the Idaho Line, 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. In the middle, the US 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 14–15 March, elements of the ROK 1st Infantry Division and the US 3rd Infantry Division liberated Seoul, marking the fourth and last time the capital changed hands since June 1950. The PVA/KPA 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 PVA/KPA 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, US IX and US X Corps pushed forward methodically, IX Corps against light opposition and X Corps against staunch enemy defenses. Hongch'on was taken on the 15th and Chuncheon secured on the 22nd. The capture of Chuncheon was the last major ground objective of Operation Ripper.
UN forces had advanced north an average of from their start lines. However, while the Eighth Army had occupied their principal geographic objectives, the goal of destroying PVA forces and equipment had again proved elusive. More often than not, the PVA/KPA forces withdrew before they suffered extensive damage. Chuncheon, a major PVA/KPA supply hub, was empty by the time UN forces finally occupied it. As the UN 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.
Background
As Operation Killer had entered its final week with limited results already predictable, Ridgway published plans for another attack, again with the main effort in his central zone, but with all units on the Eighth Army front involved. As in Operation Killer, the primary purposes of the attack, which Ridgway called Operation Ripper, were to destroy PVA/KPA forces and equipment and to interdict their attempts to organize an offensive. A secondary purpose was to outflank Seoul and the area north of the city as far as the Imjin River. Aware of UN commander General Douglas MacArthur’s interest in recapturing Seoul, but preferring to avoid a direct assault across the Han River into the capital (although plans had been prepared for such an operation), Ridgway hoped to gain a position from which he could take Seoul and the ground to the north by a flanking attack from the east or simply by posing a threat that would induce enemy forces to withdraw from that area.
Ridgway published the Ripper plan on 1 March but deferred setting an opening date because of forward area supply shortages, particularly in food, petroleum products, and ammunition. The shortages resulted partially from conscious efforts during February, especially during the Chinese Fourth Phase Offensive in mid-February, to hold down stockpiles in forward dumps as a hedge against losses through forced abandonment or destruction. In addition, as stocks were expended in the Killer advance, the damage to roads, rail lines, bridges, and tunnels caused by the rains and melting ice and snow severely hampered resupply. Before setting a date for the operation Ridgway wanted a five-day level of supplies established at all forward points. The best estimate at the beginning of March was that this level could be reached in about five days.