The Battle of Cedar Mountain was also fought by this corps, alone and unassisted; and, although defeated by the overwhelming force of the enemy, the record shows that the two divisions did some of the best fighting of the war there.

In that battle the divisions were commanded by Generals Williams and Christopher C. Augur; loss, 302 killed, 1,320 wounded, and 594 missing; total, 2,216, out of less than 6,000 engaged.

Nathaniel Banks was relieved of command and replaced by Joseph K. Mansfield, an old Regular Army veteran with 40 years of service.

Its depleted columns had been strengthened by the accession of five new regiments of volunteers fresh from the North, three of which were composed of Pennsylvanians enlisted for nine months only.

The corps now numbered 12,300 present for duty, including the non-combatants; it contained 22 regiments of infantry and three batteries of light artillery.

The vacancy caused by the death of General Mansfield was filled by the appointment of Maj. Gen. Henry W. Slocum, a division commander of the VI Corps, who had already achieved a brilliant reputation by his services on in the Peninsula Campaign, and at the successful storming of Crampton's Gap.

On the afternoon of July 2 the corps was ordered by army commander George G. Meade to disengage from Culp's Hill and reinforce the Union line on its extreme left flank, near Little Round Top.

To this must be added the losses suffered in the 14 regiments from the brigades of William Smith, Junius Daniel, and Edward A. O'Neal, which were sent to Johnson's support.

After the Gettysburg Campaign, the Army of the Potomac pursued Robert E. Lee into Virginia, the XII Corps joining in the pursuit, pushing forward until it reached the Rappahannock.

While encamped there, on September 23, 1863, the XI and XII corps were detached from the army and ordered to Tennessee as a reinforcement for William Rosecrans, besieged in Chattanooga.

On the night of October 27, his division bivouacked in Lookout Valley, in an advanced and isolated position, where he was attacked at midnight by a part of James Longstreet's command.

General George H. Thomas, commanding the Army of the Cumberland, stated in his official report that "the repulse by Geary's Division of greatly superior numbers who attempted to surprise him, will rank among the most distinguished feats of arms of this war."

This action of the War Department was based on the small sizes of the two corps: the XI had been extremely damaged at Gettysburg and the XII had always been the smallest in the army.