South Korea participated in the Vietnam War as America’s ally on a tremendous scale involving over 300,000 soldiers from 1964-1973. Despite this massive commitment, South Korea’s involvement has attracted little scholarly interest or public attention. The prevailing explanation in relevant historiography often dismisses South Korea’s role as a mercenary exchange taken under U.S. pressure or in pursuit of economic incentives. Alternatively, I argue that the South Korean government had a legitimate national interest in participating in the Vietnam War in pursuit of political, national defense, and economic advancements that were uniquely motivated by concurrent hostilities with North Korea. South Korea’s national interests aligned with the U.S. such that they willingly and effectively contributed to the Vietnam War. By the war’s end, U.S. and South Korean national interests diverged sharply as relations declined, which left South Korea’s wartime role as an embattled and largely forgotten memory in the U.S.