On August 20, 1861, Major General George McClellan issued General Orders, No. 1 (Army of the Potomac) announcing that he was assuming command of the newly-created Army of the Potomac.
General Orders, No. 1
Headquarters Army of the Potomac
Washington, August 20, 1861.
In accordance with General Order, No. 15, of August 17th, 1861, from the Headquarters of the Army, I hereby assume command of the Army of the Potomac, comprising the troops serving in the former Departments of Washington and Northeastern Virginia, in the Valley of the Shenandoah, and in the States of Maryland and Delaware.
The organization and command into divisions and brigades will be announced hereafter.
The following named officers are attached to the Staff of the Army of the Potomac:
Major S. Williams, Assistant Adjutant General.
Captain A.V. Colburn, Assistant Adjutant General.
Col. T.M. Key, Aid-de-Camp.
Captain N.B. Sweitzer, 1st Cavalry, Aid-de-Camp.
Captain Edward McK. Hudson, 14th Infantry, Aid-de-Camp.
Captain Lawrence A. Williams, 10th Infantry, Aid-de-Camp.
Major A.J. Mayer, Signal Officer.
Major H.F. Clarke, Chief Commissary.
Surgeon C.S. Tripler, Medical Director.
Major J.G. Barnard, Chief Engineer.
Major J.N. Macomb, Chief Topographical Engineer.
Captain C.P. Kingsbury, Chief of Ordnance.
Brigadier General Geo. Stoneman, Volunteer service, Chief of Cavalry.
Brigadier General W.F. Barry, Volunteer service, Chief of Artillery.
Geo. B. McClellan
Major General U.S. Army