The Eighth United States Army (EUSA or Eighth Army) was the field army which served as the commanding formation for ground forces operations during the Korean War. Formed in 1944, EUSA units fought in the Southwest Pacific campaign and then in the Philippines before arriving in Japan in 1945 where it assumed responsibility as the occupying force there.
When North Korea invaded South Korea in 1950, and it became clear that US ground force intervention was necessary, units from the Eighth Army occupation forces in Japan were the first to be shipped to Korea. Outnumbered, lacking in training and equipment, Eighth Army units were badly mauled by the invading North Korean forces at first but eventually enough troops arrived for a determined and successful defense to be mounted and the North Korean advance was halted at the Pusan Perimeter.
As the number of troops in the Eighth Army grew, two Corps Headquarters, I Corps and IX Corps were activated to exercise better command and control over the units subordinate to Eighth Army. Later in the war, X Corps was also added to the Order of Battle of the Eighth Army.
The Eighth Army remained in South Korea after the armistice in 1953. It is still based there today, headquartered in Seoul, and it still has responsibility for the defense of South Korea.
The Eighth Army in MASHEdit
The 4077th MASH reported to I Corps which was one of the Corp Commands subordinate to the Eighth Army. As such, most of the routine administrative tasks such as daily reports and requisitions went to I Corps and not to Eighth Army. However officers from the higher Army headquarters did appear in various episodes. Whenever the MASH officers visited Tokyo where the Eighth Army Headquarters was located, they were likely to come across Eighth Army HQ personnel, as happened in "The Consultant".
In "Big Mac" it is a staff officer from Eighth Army who visits the MASH to make arrangements for General Macarthur's visit. This would be natural as the Supreme Commander's tour of the theater of operations would likely encompass the units of more than one Corps.
In "The Novocaine Mutiny" the hearing for the charges against Hawkeye is conducted by Colonel Carmichael from Eighth Army Headquarters.
Lt. Colonel Donald Penobscott, Margaret's husband in Season 6 and part of Season 7, was based in Tokyo and most likely had a billet as a staff officer somewhere in Eighth Army HQ.
In "The Merchant of Korea", the P.A. system announced that the Eighth Army had commended the 4077th MASH for its tireless efforts after three days of non-stop surgery.