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, 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. 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.

The Korean War was fought between North Korea and South Korea from 1950 to 1953. It began on 25 June 1950 when North Korea invaded South Korea and ceased after an armistice on 27 July 1953. North Korea was supported by China and the Soviet Union while South Korea was supported by the United States and US-led United Nations (UN) forces.