The following Union Army units and commanders were the initial structure on April 4, 1862 of the Union Department of the Potomac during the Peninsula campaign of the American Civil War.
This list includes units deployed to the Virginia Peninsula, and those that remained in the Washington area.
The following units were the initial organization of the Army of the Potomac on the peninsula.
Maj Granville O. Haller, Commandant of General Headquarters
Professor Thaddeus S.C. Lowe BG Edwin Sumner, Commanding Ltc Joseph H. Taylor, Adjutant First Division
The Third Division under BG Louis Blenker was detached in early April and transferred to the Mountain Department BG Samuel P. Heintzelman, Commanding Cpt Chauncey McKeever, Chief of Staff First Division
BG Daniel Butterfield Cpt Charles Griffin Second Division
BG Erasmus D. Keyes, Commanding Ltc Charles C. Suydam First Division
BG John Davidson Cpt Romeyn B. Ayres Third Division
BG Innis N. Palmer Col Guilford D. Bailey W.F.
On April 4, the First Corps was renamed the Department of the Rappahannock, with authority to include the District of Columbia, Maryland between the Potomac and Patuxent, and Virginia between the Blue Ridge and the Fredericksburg & Richmond Railroad.
MG Irvin McDowell, Commanding Ltc Edmund Schriver, Chief of Staff Unattached cavalry Sharpshooters First Division
BG John Newton Cpt Edward R. Platt Second Division
BG Edward Ord Cpt Truman Seymour Third Division
On April 4, the Fifth Corps was renamed the Department of Shenandoah with authority over Maryland between the Blue Ridge and Flintstone Creek, Virginia between the Blue Ridge and the modern-day border with West Virginia.
MG Nathaniel P. Banks, Commanding Cpt Louis H. Pelouze, Acting Assistant Adjutant General Unattached Infantry First Division
Col George Henry Gordon Cpt Clermont L. Best Second Division
Col Erastus B. Tyler Cpt Joseph C. Clark Cavalry
Shields' Division was transferred to the Department of the Rappahannock on May 10, 1862 BG James S. Wadsworth, Commanding Railroad Guards Col Dixon S. Miles On March 22, the Middle Department was created with authority over Pennsylvania, New Jersey, Delaware, and the Eastern Shore of Maryland and Virginia, as well as the Maryland counties of Cecil, Hartford, Baltimore, and Anne Arundel.
MG John A. Dix, Commanding Maj Daniel Tompkins Van Buren, Chief of Staff and Acting Assistant Adjutant General Cavalry Artillery Infantry The Department of Virginia constituted an area 60 miles from Fort Monroe.
McClellan had received permission to absorb it into his army as a division of the First Corps, but it was rescinded shortly after he arrived on the Peninsula.