It was time for McClellan to do something.
Frederick, the town in Maryland where McClellan’s headquarters was located, was about 40 miles northwest of Washington. The National Road came up from Washington, passed through Frederick, and then continued northwest towards Hagerstown for about 25 miles. From there, there are good roads dropping south into Virginia and the Shenandoah, other roads lead west into Ohio, and some go into Pennsylvania. About halfway between Frederick and Hagerstown lays South Mountain. It is not a mountain, per se, but rather a long, curving ridge that starts by the Potomac next to Harper’s Ferry and runs far into Pennsylvania and passes west of Gettysburg. From McClellan’s point of view, South Mountain was on the horizon – a dark, long curtain that separated the Union army and the Confederates. It was a veil on the far side of which lay the full power of the Confederacy, fully shielded from the prying eyes of the Federals.
McClellan had been getting some reports from his cavalry – but not in detail. The only news he knew was that the Confederate army was out there somewhere, doing something, scaring the Union population. He tried to send out his cavalry, but Jeb Stuart and his cavalry had each gap of South Mountain carefully guarded, and it would take much more than just a cavalry division to drive him away.
Of course, a general attack by McClellan’s main body would send Stuart scurrying away, but the Union commanding general thought that move dangerous. He might end up in the wrong place, leaving Lee the complete opportunity to go pouncing on rich Northern towns in Pennsylvania unopposed. Unless he knew where Lee’s army was and what he was doing, he would stay put. Lee had all the advantage up until September 13, 1862.
But now with one paper, that advantage passed from Lee to McClellan. He now held in his hands Special Orders No. 191, which was just written four days ago, detailing where the Confederate Army was and what it was doing. Right now, it was in the act of chewing up Harper’s Ferry. Stonewall Jackson’s command plus A. P. Hill’s division were detached and sent via a roundabout route across the Potomac to West Virginia to come up on Harper’s Ferry from the southwest, to occupy Bolivar Heights. John G. Walker’s division also crossed the Potomac to come up to the town from the east to occupy Loudon Heights – a little mountain that rises up from the Shenandoah’s eastern shore just south of the junction of the Shenandoah and the Potomac rivers, and which overlooks the little town of Harper’s Ferry. Two other Confederate divisions under Lafayette McLaws were to descend on Harper’s Ferry from the north and occupy Maryland Heights – a ridge that is just north of where the Shenandoah river joins the Potomac. From there, McLaws’s men could fire right down into the heart of the Union defenses at Harper’s Ferry. The rest of the army – Lee himself, Longstreet’s two divisions, D. H. Hill’s rear-guard division, the reserve artillery, and the supply trains – would wait at Boonsboro, a little town just beyond South Mountain, which the National Road passes through. With Harper’s Ferry captured, the army was to reunite again – either at Boonsboro or at Hagerstown, 12 miles up the road.
And there it was, everything, right on McClellan’s headquarters desk. The fog of war which always hinders an army commander’s ability to see the enemy had suddenly been lifted, and McClellan knew the Rebel army’s plan as well as if he was Robert E. Lee himself. When Brigadier General John Gibbon of the “Black Hat” Brigade visited McClellan’s headquarters that evening, McClellan waved the paper in front of him and said, “Now I know what to do! Here is a paper with which, if I cannot whip Bobby Lee, I will be willing to go home!”
Harper’s Ferry was doomed at the start. It was right at the bottom of a bowl – Harper’s Ferry was on all sides dominated by higher ground – and when the Confederates got to the edge, there was no stopping them. McClellan had ordered the garrison to get out while the getting was good, but General-in-Chief Henry Halleck had countermanded that order and told the garrison to stay put. McClellan had been confused – why would Halleck want to do that? But now, unintentionally, Halleck had set a trap and Lee had stumbled right into it. For by spending precious time trying to do away with the Harper’s Ferry, McClellan was being handed the greatest opportunity for any Union general in the entire war.
The reason was that Lee’s army was in complete disarray. He had divided his army into four parts, the closest part to McClellan heavily outnumbered. Lee had based his whole strategy on the fact that McClellan was extremely cautious, but with his own orders in the enemy’s hands, that weight of that fact had diminished.
“[McClellan] was closer to [Lee’s] scattered pieces than those pieces were to each other. Lee was entirely at his mercy. There was nothing to keep the Army of the Potomac from breaking through the mountain wall and stamping out those separated segments of Lee’s army one at a time. The Army of Northern Virginia could be destroyed, which would win the war overnight.”
-Bruce Catton, Mr. Lincoln’s Army
McClellan would have to move very fast. The orders were four days old already, and the Union high command had figured out long ago that the Confederate army could do a good deal of marching in four days. If McClellan wanted to take advantage of his opportunity at all, he would have to do it fast.
But it was actually better for McClellan than it seemed. It had been believed by Lee that since everyone was moving by the 10th that on the 12th, Jackson would be positioned on Bolivar Heights, McLaws would be firing his cannons down from Maryland Heights, and Walker would at least have infantry on Loudon Heights. But it was not so. No, not even Jackson’s vaunted foot cavalry could march that fast. Only now, on the 13th, was Jackson even in sight of the Union garrison at Harper’s Ferry, and it would take another day to get deployed. Only now was McLaws fighting his way up Maryland Heights, and only now was Walker climbing up Loudon Heights. Longstreet and the rest of the army was sent up to Hagerstown to deal with an imaginary threat from the north, leaving Boonsboro unprotected. The only unit left near the Union army was the division of D. H. Hill, which was so war-torn that it barely measured more than five thousand. Lee’s army was supposed to be united at Boonsboro by now, but it was not at all united – rather, it was scattered across the map. Now was the time for McClellan to strike.
So he made his preparations. His main objective was simple: Just get across South Mountain while Lee’s army was still scattered, overwhelm his fragments one by one, and then turn south and relieve Harper’s Ferry. In the end, some 14,000 fresh troops would be added to the almighty strength of the Army of the Potomac.
Only two of all the roads which crossed South Mountain really mattered right now. The first, the National Road, went from Frederick and passed through a gap, Turner’s Gap, in the ridge, and then went on to Boonsboro and Hagerstown. The other was one that branched off to the south and west, crossed the mountain at Crampton’s Gap, and emerged on the other side just five miles northeast of Harper’s Ferry. If he smashed through quickly at Turner’s gap, the army would descend on what McClellan thought to be Lee’s main force, but what was only three divisions. At the same time, a drive through Crampton’s Gap would overwhelm McLaws’s two divisions and open the back door through which the Harper’s Ferry garrison could escape.
Conveniently located some miles east of Crampton’s Gap was William B. Franklin’s VI Corps of two divisions, plus Couch’s division of the IV Corps – some eighteen thousand men in all. McClellan deemed this force large enough to destroy McLaws and to come and rescue the Harper’s Ferry troops. So Franklin was instructed to make a racket with his artillery, even though there was nothing to shoot at, to let the commander at Harper’s Ferry know that help was on its way.
Meanwhile, the rest of the army, about seventy thousand men, would go straight through Turner’s Gap and attack Lee’s main body. He got this force up and ready.
So in the evening of the 13th, the advance guard of the army – General Cox’s Ohio division of Jesse L. Reno’s IX Corps was moving along well. Reno himself, in high spirits, was urging the Ohioans across the Cacoctin range, a small ridge that sits right in between Frederick and South Mountain. By dark, Cox’s division was across and bedding down near the village of Middletown. Rebel pickets on South Mountain notified D. H. Hill in Boonsboro that quite a lot of Yankees were coming up to Turner’s Gap. Federal cavalry skirmished with Confederate patrols in the valley and on the slope of South Mountain and sent back reports that the only substantial forces at Turner’s Gap were cavalry.
McClellan, meanwhile, was laboring over orders for the rest of the army – chiefly for Franklin’s corps. The VI Corps was at a place called Buckeystown, some six miles south of Frederick and 12 miles east of Crampton’s Gap. McClellan told him the details of his South Mountain plan – he told him how he found Special Orders 191 and explained the positions of the Confederates. Reno and the rest of the army was at Turner’s Gap and would smash through in the morning. Franklin was to start “at daybreak in the morning” for Crampton’s Gap. When he got through, his priority was to “cut off, destroy or capture McLaws’ command and relieve the Union troops at Harper’s Ferry.” After that, depending on time, he would either move north to Boonsboro and rejoin the rest of the army, or move west to Sharpsburg and cut off Lee’s retreat. At the end of the letter, to make himself clear, McClellan said: “My general idea is to cut the enemy in two and beat him in detail.”
That was all well and good. But although the orders gave Franklin a perfect idea of what he needed to do and a clear image of everything ahead of him, nowhere in the letter did it explain the extreme urgency of the moment. For the door of good fortune for McClellan was beginning to swing shut. McClellan didn’t just have a strategic advantage – he had the power to destroy Lee’s entire army. So every minute spent sitting around was a minute wasted. And Franklin did a good deal of sitting around. In the orders, it said for him to march at daybreak in the morning, but what if Franklin had marched that evening, come up to Crampton’s Gap, and be at ready to attack in the morning? That would have been a thousand times better.
But Franklin was no man to exceed expectations. He did just what he was ordered to do, which was to march in the morning. He was a good, loyal, and capable general, but a general who did note have that extraordinary little ‘spark’ that generals like Hancock or Hooker or Kearny had. So on the morning of September 14, Franklin’s corps broke camp at daybreak just as ordered, and started off on the 12-mile march to Crampton’s Gap. No one knows how history would have been changed had Franklin gotten off to an early start.
On the other side of Crampton’s Gap, there is a neat little open area two or three miles wide named Pleasant Valley, to the west side of which is a ridge which looks not unlike a camel, named Elk Mountain. The southern end of Elk Mountain is called Maryland Heights, which looks down on Harper’s Ferry, on Miles’s garrison. And that is where the biggest surrender of U. S. troops during the entire Civil War occurred.
Source: The Army of the Potomac: Mr. Lincoln’s Army – Bruce Catton