Executive Order—President's General War Order No. 3
Ordered, That no change of the base of operations of the Army of the Potomac shall be made without leaving in and about Washington such a force as in the opinion of the General in Chief and the commanders of all the army corps shall leave said city entirely secure.
That no more than two army corps (about 50,000 troops) of said Army of the Potomac shall be moved en route for a new base of operations until the navigation of the Potomac from Washington to the Chesapeake Bay shall be freed from enemy's batteries and other obstructions, or until the President shall hereafter give express permission.
That any movements as aforesaid en route for a new base of operations which may be ordered by the General in Chief, and which may be intended to move upon the Chesapeake Bay, shall begin to move upon the bay as early as the 18th day of March instant, and the General in Chief shall be responsible that it so move as early as that day.
Ordered, That the Army and Navy cooperate in an immediate effort to capture the enemy's batteries upon the Potomac between Washington and the Chesapeake Bay.
Abraham Lincoln, Executive Order—President's General War Order No. 3 Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/202517