Which country, after the US, contributed the most troops to the Vietnam War?

After the United States, South Korea contributed the most troops to the Vietnam War. The Republic of Korea deployed roughly 320,000 personnel to South Vietnam between 1964 and 1973, making it the largest foreign military contributor after the United States.

South Korea initially sent a mobile surgical hospital and Taekwondo instructors in 1964. Combat forces followed in 1965, including the Capital Division, known as the Tiger Division, and the 9th Infantry Division, known as the White Horse Division. South Korean Marines, often called Blue Dragons, also served in combat.

The deployment strengthened the U.S.–South Korean alliance and brought Seoul substantial American economic and military support. More than 5,000 South Korean personnel were killed, while nearly 11,000 were wounded. South Korean units also remain part of difficult historical discussions about alleged civilian massacres in Vietnam.

Australia, Thailand, the Philippines, and New Zealand also supported South Vietnam, but each sent far fewer troops. The key distinction is cumulative deployment over the war, not the number of soldiers present at one particular moment.