With the exception of First Bull Run the 20th participated in all of the major battles and many of the smaller battles fought by the Army of the Potomac. Their baptism of fire occurred at Ball's Bluff on October 21, 1861. Other battles included the Seven Days, Antietam, Fredericksburg, Chancellorsville, Gettysburg, the Wilderness, Spotsylvania Court House the Siege of Petersburg and the Appomattox Campaign.