The Battle of Unsan (), also known as the Battle of Yunshan (), was a series of engagements of the Korean War that took place from 25 October to 4 November 1950 near Unsan, North Pyongan province in present-day North Korea. As part of the People's Republic of China's First Phase Campaign, the People's Volunteer Army (PVA) made repeated attacks against the Republic of Korea Army (ROK) 1st Infantry Division near Unsan beginning on 25 October, in an attempt to take advancing United Nations Command (UNC) forces by surprise. In an encounter with the United States military, the PVA 39th Corps attacked the unprepared U.S. 8th Cavalry Regiment in Unsan on 1 November, resulting in one of the most devastating U.S. losses of the war.
Background
By October 1950, the UNC forces had successfully broken out of the Pusan Perimeter in the extreme south of Korea and the begun a northward advance liberating South Korea and then advancing through North Korea towards the Sino-Korean border, chasing the retreating North Korean Korean People's Army (KPA). The U.S. 1st Cavalry Division entered Pyongyang on 19 October, while the ROK were rushing towards the Yalu River in all directions. As part of the Thanksgiving Offensive to end the war, Major General Frank W. Milburn, commander of U.S. I Corps, ordered the ROK 1st Infantry Division to secure the Sui-ho Dam on the Yalu River by advancing through Unsan.
Alarmed by the rapid collapse of the KPA and UNC military forces approaching the Chinese border, Chairman Mao Zedong ordered the People's Liberation Army North East Frontier Force to be reorganized into the People's Volunteer Army (PVA) for the upcoming intervention in Korea. Despite Mao's determination to save North Korea from capitulation, the Chinese military leadership expressed doubts on the ability of the Chinese army to fight against the more modernized U.S. forces. As a compromise, Mao authorized the First Phase Campaign, a bridgehead building operation with limited offensives against only the South Korean forces while avoiding contacts with the U.S. forces. Under strict secrecy, the PVA entered Korea on 19 October.
Prelude
Locations and terrain
Unsan is a town in northwest Korea, and it is located from the Ch'ongch'on River mouth on the Korean west coast. Because of the hilly terrain at the Sino-Korean Border, Unsan is one of the few access points into the Yalu River area. The town is surrounded by hills to the north, the Nammyon River to the west and the Samtan River to the east. At the south of the town, a road junction controls the road from Unsan to Ipsok while a ridge dubbed "Bugle Hill" controls the road between Unsan and Yongsan-dong. Those two roads formed the only retreat routes for the UN forces at Unsan.
Forces and strategy
Acting on Milburn's instruction, the ROK 1st Infantry Division advanced north on 24 October with the ROK 6th Infantry Division on its right and the U.S. 24th Infantry Division on its left, and by the morning of 25 October, the ROK 1st Infantry Division had captured Unsan. But with the UNC forces spread thinly across Korea, a gap was left between the U.S. 24th Division and ROK 1st Division, leaving the ROK left flank unprotected.
Upon noticing the thinly held UNC frontline, the Chinese decided to launch a pincer movement against the South Koreans at Unsan. As part of the First Phase Campaign, the PVA 120th Division of the 40th Corps was at first to block and hold the ROK 1st Infantry Division at Unsan. Simultaneously, the bulk of the 40th Corps, together with the PVA 38th Corps and one division from the 42nd Corps, would attack and destroy the ROK 6th and 8th Infantry Divisions at the east of Unsan. Finally, the PVA 39th Corps would destroy the ROK 1st Infantry Division by infiltrating the gap between U.S. 24th Division and the ROK 1st Infantry Division west of Unsan. Undetected by UNC intelligence, the 120th Division arrived at the blocking position on 24 October, with its 360th Regiment heavily fortified the hills north of Unsan. To obscure troop movements and to prevent UNC air raids, the Chinese also started several forest fires around the end of October.