 Mize was subsequently transferred to Washington, D.C., where he serves at Headquarters Marine Corps as a special plans officer, Armed Forces Special Weapons Project, Defense Atomic Support Agency.While in this capacity, he was promoted to the rank of lieutenant colonel in July 1960 and ordered to the Marine Corps Schools, Quantico in order to attend the Senior course, which he completed in June 1961.He then rejoined 3rd Marine Division under the command of major general Donald M. Weller and served as assistant operations officer until October 1962.