When the 1st Infantry Division deployed to Vietnam in 1965, additional maneuver battalions were required; thus two infantry battalions from the 2nd Brigade, 5th Infantry Division, at Fort Devens, Massachusetts, were relieved and assigned to "The Big Red One."^[14] In September 1965, the 2nd Brigade, 5th Infantry Division was moved, minus personnel, to Fort Carson, Colorado, and refilled there. The remaining personnel at Fort Devens formed the basis of the 196th Infantry Brigade.

By 1968 the division was stationed at Fort Carson, Colorado, as a mechanized formation.^[15] 1st Brigade, 5th Infantry Division was dispatched to Vietnam after the Tet Offensive to replace a U.S. Marine Corps unit. The brigade, consisting of one battalion each of infantry, mechanized infantry, and armor, served there from July 1968 until 1971. Combat units included 1st Battalion, 11th Infantry; 1st Battalion, 61st Infantry (Mechanized); 1st Battalion, 77th Armor; A Troop, 4th Squadron, 12th Cavalry; and 5th Battalion, 4th Artillery.(Society of the Fifth Division) On 22 August 1971, the colors of 1st Brigade, 5th Infantry Division were cased and the brigade was inactivated at Fort Carson. Its final assignment was to III Corps, with the mission of reinforcing Europe if a general war was to break out there.^[16] In September 1969 the 4th Brigade, 5th Infantry Division was activated at Fort Carson, although, on the later return of 4th Infantry Division home from Vietnam in December 1970, the 4th Division replaced the 5th Division at Fort Carson, whereupon the 5th Division was inactivated.