Operation Ripper, also known as the Fourth Battle of Seoul, 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, 50 miles (80 km) east of Seoul, and Chuncheon, 15 miles (24 km) 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.

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 skilful 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.