Upon the return from Mine Run, the corps, went into winter-quarters at Brandy Station. On March 23, 1864, tile order was issued for the discontinuance of the Third and First Corps. Unjust and ill-advised, it awoke a feeling of indignation and bitter resentment that has never been forgotten by the men. The wearers of the diamond badge gloried in the record of their corps; on all occasions they proudly avowed their connection with it; they considered it second to none, and gazed with pride on the historic names emblazoned on their flags. All this, however, counted for naught at the War Department; the order was enforced, and the war-worn regiments marched away to fight under other banners; the old corps lived only in the story of its deeds that nightly were recounted around the camp-fires of its veterans. The First and Second Divisions were transferred entire to the Second Corps, and, with Generals Birney and Mott in command, became respectively the Third and Fourth Divisions of that corps. The men were allowed to retain the old diamond-shaped, flannel badges on their caps, a prudent concession under the circumstances. The Third Division was transferred entire to the Sixth Corps, where, under command of General Ricketts, it became the Third Division of that corps.
（Army of the Potomac.)
- Siege of Yorktown -- Lee's Mills -- Williamsburg -- Seven Pines -- Fair Oaks -- Oak Grove -- Seven Days battle -- Malvern Hill -- Antietam.
Organized under General Orders No. 101, March 13, 1862, by which the First, Second, and Third Corps were also created. It was formed by the divisions of Couch, Smith, and Casey, with General E. D. Keyes in command of the corps. The returns for March 31, 1862, show that the Fourth Corps then numbered, in the aggregate, 37,910, with 60 pieces of artillery; of this number, there were 32,919 present for duty. The corps moved to the Peninsula in March, 1862, with General McClellan's Army, taking part in the siege operations at Yorktown, and participating in the battle of Williamsburg, where it sustained a slight loss only. On May 18th, General Wm. F. Smith's Division was detached and assigned to the newly formed Sixth Corps, leaving the Fourth Corps to consist of the divisions of Generals Couch and Casey. After this reduction, it numbered on May 31st, 25,317 present and absent, with 17,132 present for duty; the artillery numbered 38 guns. At the battle of Seven Pines (Fair Oaks) the full force of the Confederate attack was directed on an advanced position held by Casey's Division, which stood its ground for an hour, inflicting a severe loss on the enemy, and not retiring until sufficient supports had arrived to save the day. Couch's Division was also hotly engaged, the losses in the corps aggregating 384 killed, 1,747 wounded, and 466; missing; total, 2,597 out of less than 12,000 engaged. Over half the loss at Fair Oaks fell on the Fourth Corps. During the Seven Days Battle, the corps guarded the trains during their withdrawal to the new base of supplies, but Couch's Division took a prominent part in the battle of Malvern Hill, losing over 600, killed or wounded there. When the army was ordered to abandon its position before Richmond, the Fourth Corps was divided. Couch's (1st) Division accompanied the Army of the Potomac on the Maryland campaign, some of the regiments becoming slightly engaged at Antietam. After that battle, Couch's Division was transferred, entire, to the Sixth Corps, becoming the Third Division of that corps, with General John Newton commanding the division. General Couch was promoted to the command of the Second Corps.