The Joint Staff assists the Chairman of the Joint Chiefs of Staff in accomplishing his responsibilities for: the unified strategic direction of the combatant forces; their operation under unified command; and for their integration into an efficient team of land, naval, and air forces. The "Joint Staff" is composed of approximately equal numbers of officers from the Army, Navy and Marine Corps and Air Force. In practice, the Marines make up about 20 percent of the number allocated to the Navy. Since its establishment in 1947, statute has prohibited the Joint Staff from operating or organizing as an overall armed forces general staff; therefore, the Joint Staff has no executive authority over combatant forces. The Chairman of the Joint Chiefs of Staff (CJCS) is the highest-ranking military officer in the United States Armed Forces and is the principal military advisor to the President, the National Security Council, and the Secretary of Defense. U.S. Army Gen. Mark A. Milley is the 20th Chairman of the Joint Chiefs of Staff. The Joint Chiefs of Staff consist of the Chairman, the Vice Chairman, 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. The collective body of the Joint Chiefs of Staff (JCS) is headed by the Chairman (or the Vice Chairman in the Chairman's absence), who sets the agenda and presides over JCS meetings. Responsibilities as members of the Joint Chiefs of Staff take precedence over duties as the Chiefs of Military Services. The Chairman of the Joint Chiefs of Staff is the principal military adviser to the President, Secretary of Defense, and the National Security Council (NSC), however, all JCS members are by law military advisers, and they may respond to a request or voluntarily submit, through the Chairman, advice or opinions to the President, the Secretary of Defense, or NSC.