The attack rippled down the line, leaving trampled cornfields and burning farmhouses in its wake. In among the broken stalks of a harvest that would never be gleaned lay scattered the bodies of the fallen. It was September 17, 1862, and before the sun went down along the banks of Antietam Creek more than 4,000 men would be dead.
It was late morning now and much of the killing and maiming was still to come. The men of Brigadier General Thomas F. Meagher's Irish Brigade of the First Division of the Army of the Potomac's II Corps dropped their excess equipment and double-quicked across the Roulette farm towards a sunken lane full of Rebels. After dismantling a fence under artillery fire and brushing aside retreating Yankees, the Irishmen pushed forward rapidly, attempting to close the distance between them and the enemy. The closer Meagher's men got, the more effective their .69-caliber smoothbore muskets, loaded with "buck-and-ball" cartridges, would be.
Before reaching the main Confederate position, the brigade encountered Colonel Carnot Posey's Mississippi brigade, which had left the relative security of the road to pursue a retreating Union regiment. The Irishmen leveled their muskets and blasted Posey's men with buckshot and bullets, shooting the Sixteenth Mississippi Infantry to shreds and routing the rest of Posey's command. Pushing within thirty yards of the Grayback line, the Irish Brigade slugged it out in a standup fight. The Irish took heavy casualties, but held their formation until they ran out