Minus its leader, von Gilsa's regiment served in the brigade of Julius Stahel under Maj. Gen. Franz Sigel in the Second Battle of Bull Run. When Sigel's command became XI Corps, Army of the Potomac in late 1862, the De Kalbs were in First Brigade of Stahel's First Division. Von Gilsa, after recuperating, became brigade commander in this period. Following the Battle of Antietam, he assigned the De Kalb Regiment to take part in a reconnaissance led by Sigel into Virginia.