Much has been documented about US soldiers' involvement in the Korean War. In this memoir, one officer details the little-known events of the battle of the Koto-ri Pass in North Korea in 1950. Chosin Reservoir narrates the role of the First Platoon, Battery A, Fiftieth AAA Battalion, X Corps, US Army, in facilitating the withdrawal of the First Marine Division from the Chosin Reservoir. Providing firsthand insight into the realities of war, author Merrill Harper, a retired lieutenant colonel of the US Army, tells the story of how one army officer and three enlisted men were able to break up a ten thousand man Chinese ambush on Koto-ri Pass, killing 7,500 Chinese and running the rest over the next mountains within six hours. In addition to chronicling the war-related events in North Korea in 1950, Harper, a soldier who was wounded twenty-four times, discusses his career leading up to the battle and shares other details from his twenty-two years of service in the military.