16 U.S.C. § 412 : US Code - Section 412: Camps for military instruction; regulations for militia

Search 16 U.S.C. § 412 : US Code - Section 412: Camps for military instruction; regulations for militia

The Secretary of the Army is authorized, within the limits of
appropriations which may from time to time be available for such
purpose, to assemble, at his discretion, in camp at such season of
the year and for such period as he may designate, at such field of
military maneuvers, such portions of the military forces of the
United States as he may think best, to receive military instruction
there.
The Secretary of the Army is further authorized to make and
publish regulations governing the assembling of the National Guard
or militia of the several States upon the maneuvering grounds, and
he may detail instructors from the Regular Army for such forces
during their exercises.