Colin Powell served in a body of the United States Department of Defense.
Chairman of the Joint Chiefs of Staff . The Chairman convenes the meetings and coordinates the efforts of the Joint Chiefs of Staff ( JCS ) , an advisory body within the Department of Defense comprising the Chairman , the Vice Chairman of the Joint Chiefs of Staff , the Chief of Staff of the Army , the Chief of Naval Operations , the Chief of Staff of the Air Force , the Commandant of the Marine Corps , and the Chief of the National Guard Bureau . Colin Powell . His last assignment , from October 1 , 1989 to September 30 , 1993 , was as the 12th Chairman of the Joint Chiefs of Staff , the highest military position in the Department of Defense . The Joint Chiefs of Staff ( JCS ) is a body of senior uniformed leaders in the United States Department of Defense who advise the President of the United States , the Secretary of Defense , the Homeland Security Council and the National Security Council on military matters .