Corporal Hamilton and his Company A of the 5th PA Reserves fought in a sharp, fierce action charging up steep, rocky terrain at South Mountain. They then marched along with the rest of Seymour's First Brigade of Pennsylvania Reserve regiments in Meade's 3rd Division of Hooker's I Corps to Sharpsburg. On the early evening of Sept. 16th, they came down the Smoketown Road to the East Woods, bordering on the north east and east side of the cornfield to be become infamous the next day.
(The edge of the East Woods)
The 5th PA Reserves formed the extreme left of the I Corps. There was heavy skirmishing that night, and Col. Fisher reconnoitered the ground to the east of the woods, coming into contact with the 4th Alabama in the darkness. Early the next morning, Sept. 17th, the 5th advanced through the east edge of the East Woods, driving out any Confederates and supporting the left of the 13th PA (the "Bucktail" regiment). Moving just to the east of the Smoketown Road, the 5th emerged at the south-east corner of the East Woods.
According to Ezra Carmen, the 5th PA Reserves "lining up behind the fence, opened fire upon Trimble's Brigade, in line across the plowed field near the Mumma grave-yard, 300 yards distant. The fighting was severe, the Confederates suffering most, being on open ground, while the Pennsylvanians had the cover of trees."
At this point the Bucktails ran out of ammunition and pulled back to be relieved by the 2nd Reserves. Col. Fisher saw the 13th pull back but not the 2nd coming into the line. Apparently, believing his right was gone, leaving the 5th exposed now on the right as well as left, Fisher led his regiment back through the East Woods and out of action for the rest of the day.