Battle of Seven Pines
Following the Battle of Seven Pines, the regiment was officially transferred to the Army of the Potomac, under General McClellan. The regiment was assigned to the 1st Brigade ("Robinson's Brigade"), of the 3rd Division (Kearney's Division), of the III Corps, commanded by General Samuel P. Heintzelman. Although the commanders of the Brigade, Division, and Corps changed throughout the war, the 20th was never reassigned.