((a)) The Headquarters, Marine Corps, shall furnish professional assistance to the Secretary, the Under Secretary, and the Assistant Secretaries of the Navy and to the Commandant of the Marine Corps.
((b)) Under the authority, direction, and control of the Secretary of the Navy, the Headquarters, Marine Corps, shall—
((1)) subject to subsections (c) and (d) of , prepare for such employment of the Marine Corps, and for such recruiting, organizing, supplying, equipping (including research and development), training, servicing, mobilizing, demobilizing, administering, and maintaining of the Marine Corps, as will assist in the execution of any power, duty, or function of the Secretary or the Commandant;
((2)) investigate and report upon the efficiency of the Marine Corps and its preparation to support military operations by combatant commanders;
((3)) prepare detailed instructions for the execution of approved plans and supervise the execution of those plans and instructions;
((4)) as directed by the Secretary or the Commandant, coordinate the action of organizations of the Marine Corps; and
((5)) perform such other duties, not otherwise assigned by law, as may be prescribed by the Secretary.