100th Pennsylvania Infantry

"The Battle of South Mountain was a victory for Orlando Willcox's men. Welsh's Brigade, with the Roundheads, attacked a strong Confederate line at Fox's Gap and were successful in driving the enemy from the field. The assault was made over difficult terrain, requiring an advance over steep uphill country."

"The Battle of Antietam on September 17, 1862 proved to be the single-most bloodiest day in the Civil War. The Roundheads were assigned as skirmishers for Welsh's Brigade, and succeeded in driving the Confederates before them into the outskirts of the village of Sharpsburg. The arrival of A.P. Hill's Confederates forced the withdrawal of the entire Ninth Corps back to the Antietam ... Because the 100th Pennsylvania regiment was assigned as skirmishers rather than as part of an assaulting brigade, it was fortunately not as severe a battle for them compared to other regiments. Only two men were killed or mortally wounded in this battle."
(from Gavin)

Initial Strength: not known; Killed in Action (KIA): 9; Wounded (WIA): 32;

Detail Map #7: Burnside Attacks the Lower Bridge (10 am-1 pm)
Detail Map #12: Burnside's Ninth Corps Climbs Toward Sharpsburg (3-4 pm)
Detail Map #13: AP Hill's Division Hits Burnside's Flank (4-5 pm)

Tablet #56: Ninth Army Corps - 15 Sep, 7 AM to 16 Sep, 3 PM
Tablet #62: Willcox's Division, Ninth Army Corps - 16 Sep, 9 PM to 18 Sep, 6 PM
Tablet #122: Army of the Potomac - 17 Sep, 10 AM to 17 Sep, 6 PM
Tablet #99: Willcox's Division, Ninth Army Corps - 17 Sep, 2 PM to 18 Sep, 9 AM
Tablet #70, cont: Ninth Army Corps - 17 Sep, 3 PM to 17 Sep, 5 PM
Tablet #70: Ninth Army Corps - 17 Sep, 7 AM to 17 Sep, 3 PM
Tablet #57: Ninth Army Corps - 17 Sep, 7 AM to 17 Sep, 5 PM
Tablet #64: Welsh's Brigade, Willcox's Division - 17 Sep, 7 AM to 18 Sep, 5 PM

Source: Gavin, William Gilfillan, History of the 100th Pennsylvania Volunteer Regiment, The Roundhead Regiment, Morningside Books, 1989 - portions extracted online at the 100th Pennsylvania site.