The corps then marched on the Maryland Campaign, during which time it received a new division of nine month troops headed by Brig. Gen William H. French. At the Battle of Antietam the corps was heavily engaged, its casualties amounting to more than twice that of any other corps on the field. Out of 15,000 effectives, it lost 883 killed, 3,859 wounded, and 396 missing; total, 5,138. Nearly one-half of these casualties occurred in Sedgwick's 2nd Division, in its bloody and ill-planned advance on the Dunker church, an affair that was under Sumner's personal direction; this included units like the 34th New York Volunteer Infantry Regiment on the left flank of the division's 1st Brigade, as well as the 1st Minnesota Volunteer Infantry of later Gettysburg fame. The Irish Brigade, of Richardson's 1st Division, also sustained a terrible loss in its fight at the "Bloody Lane", but, at the same time, inflicted a greater one on the enemy. This allowed Colonel Francis C. Barlow to lead the 61st and 64th New York Volunteer Infantry Regiments to break through the Confederate line. Sedgwick and Richardson were both wounded in the battle; the former eventually recovered and went on to corps command, the latter succumbed to an infection a month and a half after the battle. Oliver Howard succeeded to command of Sedgwick's division, Richardson's division was taken over by Brig. Gen Winfield Hancock, brought over from the VI Corps as the ranking brigadier general in the division, John C. Caldwell, was too inexperienced and junior for the position.