Antietam at 150
Brown, John S., Army
September 17 marks the 150th anniversary of the Battle of Antietam, the bloodiest single day in American history. The battlefield, not far from Washington, D.C., still retains much of its original character. The campaign remains a case study in operational maneuver and the battle a testimony to courage under fire.
In the July issue we discussed Union GEN George B. McClellan's Peninsular Campaign and its inglorious end. Learning that McClellan was withdrawing his army by sea from the peninsula, Confederate GEN Robert E. Lee broke away and hastened to defeat Union forces in northern Virginia before McClellan could rejoin them. These were commanded by MG John Pope, a capable general but no match for Lee and his brilliant principal subordinates, Thomas J. (Stonewall) Jackson and James Longstreet. In a series of masterful maneuvers, the Confederate generals turned Pope's flank, forced him into a battle to recover his lines of communications and handed him a stinging defeat at the Second Battle of Bull Run (Second Manassas).
Union forces fell back on Washington, D.C., where they were absorbed into a larger whole that included McClellan's returning Peninsular veterans. Pope was exiled to St. Paul, Minn., there to take command of the Northwest Department. McClellan assumed command of the combined forces and did a commendable job of reorganizing, retraining and reinvigorating them. McClellan was at his best when not on the field of battle. President Abraham Lincoln had appointed Henry W. Halleck as his General in Chief in July 1862, but Halleck assumed a role as military advisor to the President rather than attempt the direct exercise of field or strategic command.
As capable as McClellan's reconstruction of the Army of the Potomac was, Union mobilization practices embodied a flaw that would continue to haunt commanders on the battlefield. Rather than placing a priority on bringing veteran regiments back up to full strength after combat losses, the Union favored raising entirely new units. Among the perceived advantages, this practice reduced the burdens of administering existing units at a distance - and offered additional command positions with consequent opportunities for patronage. During this period only 50,000 recruits replaced combat losses, whereas 420,000 went into totally new units. As a result, regiments with combat experience withered, and regiments without combat experience continued to be thrown into battle underprepared.
Lee knew he could not rest on his laurels after Second Bull Run, nor was he inclined to. On September 4 he invaded Maryland, both to retain the initiative and in the hope that Marylanders could be induced to join the Confederacy. Maryland was a slave-holding state, and sentiment for the South there was strong. The invasion offered opportunities to sever vital Union east-west rail communications, seize the critical depot of Harpers Ferry, W. Va., move the fighting away from Virginia, and operate against such major northern cities as Baltimore, Philadelphia, and Washington, D.C. Lee's aspirations were Union nightmares. McClellan alleged he did "not despair of saving the capital" but nevertheless considered it prudent to ship the "family silver" elsewhere.
On September 13 McClellan was handed a copy of Lee's Special Order No. 191. One of his soldiers had found it in an abandoned Confederate campsite and recognized its importance. This intelligence coup revealed that the Confederates would be strung out from Harpers Ferry - where Jackson was besieging a garrison of 12,000 - to Hagerstown, Md., and beyond. Little blocked McClellan's approach from Washington through Fredericksburg, Va., to cut across this line of communications. McClellan acted on this intelligence windfall, but the next day rather than immediately.
Lee, meanwhile, recognizing that critical intelligence had been compromised, speedily threw blocking forces into Turner's Gap and Crampton's Gap in Maryland while withdrawing the rest of his army in the direction of Sharpsburg on the Potomac River. …