In the Maryland Campaign, Slocum's Division made a successful charge up the side of South Mountain at Crampton's Gap, driving the enemy from a strong position; Slocum's loss was 533 (113 killed, 418 wounded, 2 missing). At Antietam, the corps was held in reserve aside from Col. William Erwin's brigade, which participated in the storming of Bloody Lane. Winfield Hancock, who commanded the 1st Brigade of William F. Smith's division, was appointed to command the 1st Division of the II Corps after its commander Maj. Gen Israel B. Richardson fell mortally wounded, as the ranking brigadier in the division, Brig. Gen John C. Caldwell, was considered too junior for division command.