This organization comprised the troops occupying the defenses of Washington. It was organized February 2, 1863, with Major-General S. P. Heintzelman in command. He was succeeded by Major-General C. C. Augur, who was in command at the time of Early's invasion in July, 1864.
At that time the Confederate troops advanced within the limits of the city of Washington, and a severe battle was fought at Fort Stevens, in the outskirts of the city. In this battle the principal part of the fighting devolved upon the Sixth Corps; but prior to its arrival, Hardin's Division of the Twenty-second Corps held the skirmish line and the outer line of works, confronting Early's advance. Hardin's troops were under fire and became engaged at various points on the line, their losses amounting to 73, killed and wounded.
The roster of the corps was continually changing, as the Department was being continually drawn upon for reinforcements for the field, thereby preventing anything like a continuous organization. At one time, the corps was commanded by Major-General Jno. G. Parke, while among its various division commanders were Generals Hardin, De Russy and Hascall.