September 16, 1862 – General Robert E. Lee concentrated his Confederate Army of Northern Virginia near Sharpsburg as Major General George B. McClellan’s Federal Army of the Potomac approached.
Following his defeat at South Mountain, Lee led the Confederates under Major Generals James Longstreet and D.H. Hill west to Sharpsburg, a hamlet among various hills and ridges between Antietam Creek and the Potomac River. Lee planned to concentrate the forces at hand before returning to Virginia, but he changed his mind when he received word that Major General Thomas J. “Stonewall” Jackson’s Confederates captured Harpers Ferry. Lee read the message and said, “That is indeed good news. Let it be announced to the troops.”
Lee had just 18,000 men, but he relied on Jackson and the rest of the Confederates at Harpers Ferry to hurry and join his army at Sharpsburg, which would give him close to 45,000. Then, pointing to the hills outside Sharpsburg, Lee told his staff, “We will make our stand on those hills.”
Lee needed to make a stand in Maryland. Retreating without a fight would demoralize the Confederacy and possibly even destroy hopes of foreign recognition. Lee was confident that, like in the Seven Days Battles, McClellan would fold in the face of aggression, having never waged an offensive battle in the war thus far.
Even with all his 45,000 men, Lee still had a very small army to face McClellan’s 90,000 Federals closing in. But Lee counted on McClellan’s usual cautiousness, and he would not be disappointed. McClellan’s troops slowly began crossing Antietam Creek, east of Sharpsburg, on the afternoon of the 15th. The entire army was across by nightfall, gathering in the hills opposite the Confederates. As Lee guessed, McClellan was in no hurry to attack.
McClellan received varying accounts of the fight at South Mountain, with some reporting that Lee had been wounded and others claiming that the entire Confederate army had been pushed back into Virginia. McClellan wired General-in-Chief Henry W. Halleck, “Lee last night stated publicly that he must admit they had been shockingly whipped.”
McClellan then boasted to his old adversary, former General-in-Chief Winfield Scott, “R.E. Lee in command. The rebels routed, and retreating in disorder.” Scott replied, “Bravo, my dear general! Twice more and it’s done.” President Abraham Lincoln read this message and replied to McClellan, “God bless you and all with you. Destroy the rebel army if possible.”
But to McClellan’s surprise, the Confederates were not retreating. They were holding their ground in the hills around Sharpsburg. McClellan did not order any reconnaissance to determine the enemy’s strength, otherwise he might have learned that the Confederates were hopelessly outnumbered and vulnerable to annihilation (which he should have already known since he had a copy of Lee’s Special Orders No. 191). McClellan vowed to attack the next day.
McClellan wrote his wife on the morning of the 16th, boasting that he “no doubt delivered Penna & Maryland.” Writing to Halleck, McClellan could “ascertain that some of the enemy are still there,” but he would not attack until he learned how many there were. He wrote Major General William B. Franklin, commanding VI Corps, “I think the enemy has abandoned the position in front of us, but the fog is so dense that I have not yet been able to determine.”
Reports continued arriving at McClellan’s headquarters stating that Lee was returning to Virginia. He shared these with Halleck, who responded, “I think you will find that the whole force of the enemy in your front has crossed the river. I fear now more than ever that they will recross at Harper’s Ferry or below, and turn your left, thus cutting you off from Washington.”
As McClellan spent the day guessing how many enemy troops he faced, two of Jackson’s divisions and Brigadier General John G. Walker’s Confederate division arrived to reinforce Lee at Sharpsburg. The troops had marched through the night to hurry there. Lee directed Jackson to take positions on the left, while Walker took the extreme right. Longstreet and D.H. Hill would hold the center and right. A.P. Hill’s division remained at Harpers Ferry, 17 miles away, paroling Federal prisoners and collecting captured supplies. That night, Lee ordered those men to hurry and join the main force as well.
The Confederates could see the enormous Federal army gathering in the hills across the fields; Longstreet called it “an awe-inspiring sight.” Lee’s army remained vastly outnumbered, but the Federals only threatened him with a light artillery barrage. Lincoln, trying to gather all the information he could, wired Pennsylvania Governor Andrew Curtin, “What do you hear from Gen. McClellan’s army?”
About 60,000 Federals had arrived by the end of the 16th, with the rest en route. The Federal army was short of medical supplies and personnel, having left most of their equipment and ambulances on the Virginia Peninsula. Hospital tents were also a rare commodity, prompting the army’s medical director, Jonathan Letterman, to commandeer homes and barns in the vicinity and prepare them to receive wounded troops.
McClellan finally drafted a plan of attack around 2 p.m., or 24 hours after arriving in the Confederates’ front. The plan called for each of the six corps commanders to report directly to McClellan rather than operate within the three wings he had created before leaving Washington. This decentralized the command structure at a time when centralization could have been much more effective.
The attack, which McClellan had said would happen on the 16th, was postponed until the morning of the 17th. Three corps would overwhelm the Confederate left, with a fourth corps in the center joining in once the left was turned. A fifth corps would move against the right to secure the Potomac River crossing, thus cutting off Lee’s escape, and the last corps would remain in reserve.
Major General Joseph Hooker’s I Corps was to begin the attack. Hooker’s Federals advanced west and took up assault positions around 4 p.m. They briefly exchanged fire with Confederates under General John Bell Hood, which indicated to Lee that McClellan would focus on that sector of the field. Rain fell during the evening as troops on both sides readied themselves for the fight.
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