((a)) The President shall assign for instruction of the National Guard such members of the Regular Army or the Regular Air Force as he considers necessary.
((b)) The Secretary of the Army may detail members of the Regular Army to attend an encampment, maneuver, or other exercise, for field or coast-defense instruction of the Army National Guard. Similarly, the Secretary of the Air Force may detail members of the Regular Air Force to attend exercises for field or coast-defense instruction of the Air National Guard. Members so detailed shall instruct the members of the National Guard at the exercise, as directed by the Secretary concerned, or as requested by the governor or commanding officer of the National Guard there assembled.