Joint Chiefs of Staff, U.S. statutory agency, created in 1949 within the Dept. of Defense. The chairman is the principal military adviser to the President, the National Security Council, and the Secretary of Defense. Members include the chairman, appointed by the President with Senate approval; the chief of staff, U.S. army; the chief of naval operations; the chief of staff, U.S. air force; the commandant of the U.S. Marine Corps, and a vice chairman who manages the Joint Staff. The chief of space operations will become a member in Dec. 2020. The Joint Chiefs prepare military plans and direct unified and other combat commands under the Secretary of Defense.