Lake Changjin (Korean: 장진호), known widely in the West as Chosin Reservoir (Japanese: 長津湖), is a lake located in Changjin County, North Korea.

The Battle of the Chosin Reservoir took place about a month after the People's Republic of China entered the Korean War and sent the People's Volunteer Army (PVA) 9th Army[a] to infiltrate the northeastern part of North Korea.

On 27 November 1950, the Chinese force surprised the US X Corps commanded by Major General Edward Almond at the Chosin Reservoir area.

Between 27 November and 13 December, 30,000[2] United Nations Command troops (later nicknamed "The Chosin Few") under the field command of Major General Oliver P. Smith were encircled and attacked by about 120,000[3] Chinese troops under the command of Song Shilun, who had been ordered by Mao Zedong to destroy the UN forces.

The UN forces were nevertheless able to break out of the encirclement and to make a fighting withdrawal to the port of Hungnam, inflicting heavy casualties on the Chinese.