Zais' assignments included Assistant Division Commander, 1st Infantry Division, United States Army, Vietnam, 1966; Director of Individual Training, Office, Deputy Chief of Staff for Personnel, United States Army, Washington, D.C., 1966–68. In that role he was instrumental in originating the concept that resulted in the creation of the noncommissioned Officer candidate program. During this time he led the army liaison team responsible for the involvement of Federal troops in suppressing the April 1968 Baltimore riot; Commanding General, 101st Airborne Division (then designated as Airmobile), Vietnam, 1968–69. He led the 101st Airborne Division in the Battle of Hamburger Hill against the People's Army of Vietnam. He then became the Commanding General, XXIV Corps, Vietnam, 1969–70.
