The Battle of Chosin Reservoir, also known as Battle of Changjin Lake (simplified Chinese: 长津湖之战; pinyin: Cháng Jīn Hū Zhī Zhàn), was a battle in the Korean War in which 30,000 United Nations (UN) troops (nicknamed "The Frozen Chosin" or "The Chosin Few") under the command of American General Ned Almond faced approximately 150,000 Chinese troops of the People's Volunteer Army 9th Army Group under the command of Song Shi-Lun. The name Chosin is the Japanese rendition of the Korean place name Changjin. The name stuck due to the Japanese names given to locations listed on maps used by UN forces.
Shortly after the People's Republic of China entered the conflict, large numbers of Chinese soldiers swept across the Yalu River, encircling the UN forces in the northeastern part of North Korea at the Chosin Reservoir. A brutal battle in freezing weather followed. Although they inflicted enormous casualties on the Chinese forces, the UN troops were forced to evacuate North Korea after they withdrew from the reservoir to the port of Hungnam.
The events of the Chosin Battle, which had a decisive impact on the future course of the war, were fought in the seventeen day period between November 27 and December 13, 1950:
the defense of Hagaru-ri,
the defense of Yudam-ni,
the effort of the 5th and 7th Marines to break through from Yudam-ni to Hagaru-ri,
the fight of RCT 31, east of Changjin
the 1st Marines / Task Force Dog seizure of hill 1081 in the vicinity of Chinhung-ni on 9 December and reconstruction of the MSR bridge and
the withdrawal to Hungnam through the protective lines of Task Force Dog, 3rd Infantry Division at Chinhung-ni.