I Corps formed a part of General John Pope's Army of Virginia, and with it the regiment participated in the Northern Virginia Campaign's First Battle of Rappahannock Station, August 22–24. Under command of Major William Henkel, the regiment actively engaged in the Second Battle of Bull Run, August 29–30, and suffered 57 casualties: 14 killed, 32 wounded (including those mortally), and 11 missing. Henkel was severely wounded, but remained on the field for three hours after he was hit. The command of the regiment devolved to Captain Frederick Braun.