Zais attended the United States Army Command and General Staff College, and was also a graduate of the Armed Forces Staff College, and the National War College. He was promoted to brigadier general on June 1, 1964; major general on May 1, 1967; and lieutenant general on August 1, 1969. He was named Commanding General, Allied Land Forces South-Eastern Europe, Izmir, Turkey, effective August 1973 following his promotion to general on July 13 the month prior.