September 9, 1862 – The Confederates resumed their advance as panic began spreading through southern Pennsylvania.
General Robert E. Lee was ready to move his Confederate Army of Northern Virginia north from Frederick, but first he needed to open lines of supply and communications to Virginia. A line through Manassas Junction could be easily disrupted by Federals guarding nearby Washington, so Lee opted to open a line into the Shenandoah Valley. To do this, he needed to capture the 12,000-man Federal garrison at Harpers Ferry, which protected the Baltimore & Ohio Railroad and the Chesapeake & Ohio Canal.
Under Lee’s Special Orders No. 191, Major General James Longstreet would lead three divisions out of Frederick toward Hagerstown, shielded by South Mountain. The rest of the army, split into three commands, would turn and cross the Potomac River, cut the B & O, and advance on Harpers Ferry from three separate directions. The garrison was to be captured within three days, at which time the three commands would join forces and rejoin the main army at either Hagerstown or Boonsboro. From there, the entire army would advance into Pennsylvania.
For the third time in his first three campaigns with the Army of Northern Virginia, Lee would defy military logic by splitting his army in the face of a larger enemy. But this time he would do it in enemy territory. Brigadier General John G. Walker, one of the three commanders slated to go to Harpers Ferry, expressed surprise that Lee would divide his army into so many pieces while Major General George B. McClellan’s Federals approached. Lee asked, “You doubtless regard it hazardous to leave McClellan practically on my line of communication, and to march into the heart of the enemy’s country?” Walker said yes. Lee replied:
“Are you acquainted with General McClellan? He is an able general, but a very cautious one. His enemies among his own people think him too much so. His army is in a very demoralized and chaotic condition, and will not be prepared for offensive operations–or he will not think so–for three or four weeks. Before that time I hope to be on the Susquehanna (River in Pennsylvania).”
Lee’s aide, Colonel Robert H. Chilton, wrote out copies of the order and delivered them to each division commander. Major General Thomas J. “Stonewall” Jackson, who formerly had Major General D.H. Hill’s division under his command, sent a second copy to Hill, who never received the copy written by Chilton. This would produce important consequences.
Lee wrote President Jefferson Davis, “I believe that the enemy are pushing a strong column up the Potomac River by Rockville and Darnestown, and by Poolesville toward Seneca Mills. I hear that the commands of (Edwin) Sumner, (Franz) Sigel, (Ambrose) Burnside, and (Joseph) Hooker are advancing in the direction above mentioned.”
This was true. General William B. Franklin’s corps was near Rockville and Darnestown, General Darius Couch was near Seneca Mills, and Burnside and Hooker were east near Cracklintown. McClellan now knew the Confederates were at Frederick, supposedly 110,000 strong but actually half that number. McClellan reported to General-in-Chief Henry W. Halleck, “They talk of going to Gettysburg and York” in Pennsylvania.
After advancing further and positioning his troops to descend on the Confederate flank, McClellan wrote, “The army is tonight well posted to act in any direction the moment the enemy develops his movements. I am now in condition to-watch him closely, and he will find it hard to escape me if he commits a blunder.”
The Confederates headed out of Frederick on the morning of the 10th. Longstreet’s three divisions and D.H. Hill’s division moved on the National road toward Hagerstown, when Lee suddenly received word that Federals from Pennsylvania were coming their way. Lee’s army was already divided into four sections, but since Hagerstown was the key to his entire plan, he divided it yet again by sending Longstreet to defend the town and Hill to guard the South Mountain passes near Boonsboro. Longstreet, who routinely protested any order that divided the army, told Lee, “General, I wish we could stand still and let the damned Yankees come to us!”
Meanwhile, the other three Confederate commands approached Harpers Ferry. Heading one of the three was Jackson, who led his men west through Turner’s Gap in South Mountain. This route required them to move through Martinsburg, but Jackson learned that Federals guarded that town, forcing him to retrace his route. This delayed part of the advance on Harpers Ferry. Meanwhile, Walker approached Loudoun Heights and General Lafayette McLaws approached Maryland Heights, two points overlooking Harpers Ferry, as planned.
When McClellan learned that Lee had abandoned Frederick, he ordered his Federals to hurry their northwest advance to catch them before they reached Pennsylvania. By the 11th, the Federals were still 15 miles from Frederick, moving an average of just six miles a day while occasionally stopping to loot civilian property.
Lee accompanied Longstreet to Hagerstown, where they found no Federals from Pennsylvania as feared. Pennsylvania Governor Andrew Curtin, terrified that the Confederates may invade his state, called for 50,000 volunteers to defend their homeland.
Anderson, Nancy Scott; Anderson, Dwight, The Generals: Ulysses S. Grant and Robert E. Lee (New York: Vintage Books, 1987), p. 325; Bailey, Ronald H., The Bloodiest Day: The Battle of Antietam (Alexandria, VA: Time-Life Books, 1983), p. 21-24, 39; CivilWarDailyGazette.com; Denney, Robert E., The Civil War Years: A Day-by-Day Chronicle (New York: Gramercy Books, 1992 [1998 edition]), p. 210-11; Fredriksen, John C., Civil War Almanac (New York: Checkmark Books, 2007), p. 205-06; Freeman, Douglas Southall, Lee (Scribner, Kindle Edition, 2008), Loc 4672-96; Krick, Robert K., Historical Times Illustrated Encyclopedia of the Civil War (New York: Harper & Row, 1986, Patricia L. Faust ed.), p. 340-41; Long, E.B. with Long, Barbara, The Civil War Day by Day (New York: Da Capo Press, Inc., 1971), p. 264; McPherson, James M., Battle Cry of Freedom: The Civil War Era (Oxford History of the United States Book 6, Oxford University Press, Kindle Edition, 1988), p. 536; Wert, Jeffry D., Historical Times Illustrated Encyclopedia of the Civil War (New York: Harper & Row, 1986, Patricia L. Faust ed.), p. 19-20