For the remainder of the war, corps were added and subtracted from the army. IV Corps was broken up after the Peninsula Campaign, with its headquarters and 2nd Division left behind in Yorktown, while its 1st Division moved north, attached to the VI Corps, in the Maryland Campaign. Those parts of the IV Corps that remained on the Peninsula were reassigned to the Department of Virginia and disbanded on October 1, 1863. Those added to the Army of the Potomac were IX Corps, XI Corps (Sigel's I Corps in the former Army of Virginia), XII Corps (Banks's II Corps from the Army of Virginia), added in 1862; and the Cavalry Corps, created in 1863. Eight of these corps (seven infantry, one cavalry) served in the army during 1863, but due to attrition and transfers, the army was reorganized in March 1864 with only four corps: II, V, VI, and Cavalry. Of the original eight, I and III Corps were disbanded due to heavy casualties and their units combined into other corps. The XI and XII Corps were ordered to the West in late 1863 to support the Chattanooga Campaign, and while there were combined into the XX Corps, never returning to the East.