During his army career, Sullivan served as: Assistant Commandant, United States Army Armor School at Fort Knox, Kentucky from November 1983 to July 1985; Deputy Commandant, United States Army Command and General Staff College at Fort Leavenworth, Kansas from March 1987 to June 1988; Commanding General, 1st Infantry Division (Mechanized) at Fort Riley, Kansas from June 1988 to July 1989; Deputy Chief of Staff for Operations and Plans; and Vice Chief of Staff of the United States Army from 1990 to 1991. His overseas assignments included four tours in Europe, two in Vietnam and one in Korea.