Vietnam War

The 4th Infantry Division deployed from Fort Lewis to Camp Holloway, Pleiku, Vietnam on 25 September 1966 and served more than four years, returning to Fort Carson, Colorado on 8 December 1970. Two brigades operated in the Central Highlands/II Corps Zone, but its 3rd Brigade, including the division's armor battalion, was sent to Tây Ninh Province northwest of Saigon to take part in Operation Attleboro (September to November 1966), and later Operation Junction City (February to May 1967), both in War Zone C. After nearly a year of combat, the 3rd Brigade's battalions officially became part of the 25th Infantry Division in exchange for the battalions of the 25th's 3rd Brigade, then in Quảng Ngãi Province as part of the division-sized Task Force Oregon.

Throughout its service in Vietnam the division conducted combat operations ranging from the western Central Highlands along the border between Cambodia and Vietnam to Qui Nhơn on the South China Sea. The division experienced intense combat against People's Army of Vietnam regular forces in the mountains surrounding Kontum in the autumn of 1967. The division's 3rd Brigade was withdrawn from Vietnam in April 1970 and deactivated at Fort Lewis. In May the remainder of the division conducted cross-border operations during the Cambodian Incursion. The division then moved to An Khe. The "Ivy Division" returned from Vietnam on 7 December 1970, and was rejoined in Fort Carson by its former 3rd Brigade from Hawaii, where it had re-deployed as part of the withdrawal of the 25th Infantry Division. One battalion remained in Vietnam as a separate organization until January 1972.