December 07, 1900
Whenever upon marches, guards, or in quarters, different corps of the army happen to join or do duty together and an official of the Marine Corps or the militia shall command the whole pursuant to the 122d article of war, such officer shall report his action and the operations of the force under his command through military channels to the Secretary of War as well as to his superiors in his own branch of the service.
WILLIAM MCKINLEY
William McKinley, Executive Order Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/205557