Following the invasion of South Korea by North Korea, twenty-one member nations of the United Nations (UN) committed themselves to support South Korea which was not yet a member nation...
Sixteen UN nations supplied fighting units and five sent military hospitals and field ambulances. Australia was one of the very first to contribute military personnel from all three services. The single largest UN contributor was the United States of America (USA) which at one stage had 140,000 personnel deployed in direct combat roles in Korea. Great Britain, Canada, France, Belgium, the Netherlands, Colombia, Ethiopia, South Africa, New Zealand, Türkiye, Greece, Thailand, Philippines and Luxembourg sent fighting units. Norway, Sweden, Denmark, India, Italy contributed military hospitals and field ambulances to the cause.
The United Nations Command (UNC) provided the core military and strategic direction for the anti-communist war effort in Korea. The USA provided the high command for the UNC as well as the vast majority of the logistics, air and naval power, artillery and military infrastructure which made possible the continuation of the war despite repeated reverses suffered due to the actions of an aggressive, determined and proficient foe. The British Commonwealth sent the next most numerous of the UN contingents. As well as Commonwealth air and naval units, the 1st British Commonwealth Division, in which Australian infantry battalions served, took part in some of the hardest-fought battles of the war.
In 1950 the armed forces of the Republic of Korea (ROK) numbered 95,000. They were poorly equipped and there was no air force. The army had no experience of combat against regular land forces. The ROK army was overwhelmed by the North Korean invasion and retreated as quickly as it could to the safety of the Pusan defensive perimeter. Recovering there, ROK units participated in the UN counterattacks following Inchon and suffered heavily in the retreat after the Chinese intervention. Organisation, equipment, training and tactical doctrine of the South Koreans were modelled on those of the US military. By August 1951 the ROK Army had grown to 357,430 personnel, the largest single contingent within the UNC. By the end of 1952 it held three-quarters of the front line. In three years of war the ROK army had recovered from catastrophic defeat to become a formidable and stalwart opponent of its communist enemies.