Battle of Antietam

Background

Robert E. Lee's Army of Northern Virginia—about 55,000 men—entered the state of Maryland on September 3, following their victory at Second Bull Run on August 30. Emboldened by success, the Confederate leadership intended to take the war into enemy territory. Lee's invasion of Maryland was intended to run simultaneously with an invasion of Kentucky by the armies of Braxton Bragg and Edmund Kirby Smith. It was also necessary for logistical reasons, as northern Virginia's farms had been stripped bare of food. Based on events such as the Baltimore riots in the spring of 1861 and the fact that President Lincoln had to pass through the city in disguise en route to his inauguration, Confederate leaders assumed that Maryland would welcome the Confederate forces warmly. They sang the tune "Maryland, My Maryland!" as they marched, but by the fall of 1862 pro-Union sentiment was winning out, especially in the western parts of the state. Civilians generally hid inside their houses as Lee's army passed through their towns, or watched in cold silence, while the Army of the Potomac was cheered and encouraged. Some Confederate politicians, including President Jefferson Davis, believed that the prospect of foreign recognition would increase if the Confederacy won a military victory on Union soil; such a victory might gain recognition and financial support from the United Kingdom and France, although there is no evidence that Lee thought the Confederacy should base its military plans on this possibility.

While McClellan's 87,000-man Army of the Potomac was moving to intercept Lee, two Union soldiers (Cpl. Barton W. Mitchell and First Sergeant John M. Bloss of the 27th Indiana Volunteer Infantry) discovered a mislaid copy of Lee's detailed battle plans—Special Order 191—wrapped around three cigars. The order indicated that Lee had divided his army and dispersed portions geographically (to Harpers Ferry, West Virginia, and Hagerstown, Maryland), thus making each subject to isolation and defeat if McClellan could move quickly enough. McClellan waited about 18 hours before deciding to take advantage of this intelligence and reposition his forces, thus squandering an opportunity to defeat Lee decisively.

There were two significant engagements in the Maryland campaign prior to the major battle of Antietam: Major General Thomas J. "Stonewall" Jackson's capture of Harpers Ferry and McClellan's assault through the Blue Ridge Mountains in the Battle of South Mountain. The former was significant because a large portion of Lee's army was absent from the start of the battle of Antietam, attending to the surrender of the Union garrison; the latter because stout Confederate defenses at two passes through the mountains delayed McClellan's advance enough for Lee to concentrate the remainder of his army at Sharpsburg.

Opposing forces

Union

Major General George B. McClellan's Army of the Potomac, bolstered by units absorbed from John Pope's Army of Virginia, included six infantry corps. The I Corps and XII Corps were units from Pope's force, the II Corps, V Corps, and VI Corps had fought with McClellan and the Army of the Potomac in the Peninsula campaign, and the IX Corps was a newer addition to the Army of the Potomac. The latter corps had seen action in North Carolina and a portion of it had fought with Pope. The VI Corps contingent included a division from the IV Corps. Earlier in the campaign, McClellan had assigned twenty-four new regiments of inexperienced troops to his army to bolster the strength of depleted veteran units. Of these green troops, eighteen regiments, totaling about 15,000 to 16,000 men, accompanied McClellan's army for the march to Antietam. Several thousand more new recruits were added to existing units, so about a quarter of McClellan's army was inexperienced and poorly trained entering the battle. The II, IX, and XII Corps received more of these troops than the other corps.

The I Corps was commanded by Major General Joseph Hooker and contained three divisions. The II Corps was commanded by Major General Edwin Vose Sumner, and contained three divisions. As a whole, the veteran elements of the corps had a reputation as a good fighting unit. The V Corps was commanded by Major General Fitz John Porter. Originally only one division of the corps accompanied McClellan, but a second was later released from the defenses of Washington, D.C. to accompany the Army of the Potomac. A third division of the corps reached McClellan the day of the battle. The VI Corps consisted of two divisions and the IV Corps detachment and was commanded by Major General William B. Franklin. These three divisions were positioned about a four-hour march away from McClellan's main body at the beginning of the battle. The IX Corps contained four divisions and was nominally commanded by Major General Ambrose Burnside, but Burnside temporarily commanded a wing of McClellan's army and active command passed to Major General Jesse Reno until his death at the battle of South Mountain, and then to Brigadier General Jacob D. Cox. The XII Corps was McClellan's smallest corps and contained two divisions. It was commanded by Brigadier General Joseph K. F. Mansfield, who took command only two days before the battle. McClellan's army also contained a cavalry division commanded by Brigadier General Alfred Pleasonton. A 2023 study by the historian D. Scott Hartwig estimates that McClellan had 72,199 men available for combat on September 17, with roughly 14,000 more arriving as reinforcements. Hartwig places I Corps strength at 9,582; II Corps strength at 16,475; V Corps strength at 9,476 with another 7,000 in the third division; 11,862 men in the VI Corps proper with another 7,219 men in the IV Corps detachment; 12,241 in the IX Corps; 8,020 in the XII Corps; and 4,543 in the Cavalry Division. This force was supported by 293 cannons available for duty.

Confederate

General Lee's Army of Northern Virginia was organized into two large infantry wings, commanded by Major Generals James Longstreet and Thomas J. "Stonewall" Jackson. Longstreet's wing was numerically larger than Jackson's. This arrangement was due to Confederate law not allowing the creation of corps. Longstreet's wing contained five divisions, led by major generals Lafayette McLaws and Richard H. Anderson and brigadier generals David Rumph Jones, John G. Walker, and John Bell Hood. Jackson's wing contained four divisions, commanded by major generals Daniel Harvey (D.H.) Hill and Ambrose Powell (A.P.) Hill, and brigadier generals Alexander R. Lawton and John R. Jones. Lee also had a Cavalry Division commanded by Major General J. E. B. Stuart and a unit of reserve artillery led by Brigadier General William Nelson Pendleton. The assignment of units between the wings of Jackson and Longstreet was flexible; at Antietam the two men commanded sectors of the battlefield and divisions fought under the commander whose geographic area they were fighting in.

The Army of Northern Virginia held morale and leadership advantages over McClellan's army, but was poorly supplied, was operating in enemy territory away from its logistical lines, and was more poorly armed. Ammunition supply was made more difficult due to units being armed with mixed types of weapons, and many Confederate soldiers were still armed with smoothbore weapons of shorter range. Many of the cannons issued to the Confederate artillery were obsolete, while the Union had modern guns. The Confederates had about 246 cannon at Antietam, although the exact number of guns issued to some of the Confederate batteries is not known. Lee's army was weakened by disease, and the historian Joseph T. Glatthaar estimates that about one-third to one-half of Lee's army was absent at Antietam due to straggling. The Confederate strength at Antietam is difficult to determine; Hartwig states that a precise figure is indiscernible, but estimates a strength of about 37,600 men.

Prelude to battle

Disposition of armies

Near the town of Sharpsburg, Lee deployed his available forces behind Antietam Creek along a low ridge, starting on September 15. While it was an effective defensive position, it was not an impregnable one. The terrain provided excellent cover for infantrymen, with rail and stone fences, outcroppings of limestone, little hollows and swales. The creek to their front was only a minor barrier, ranging from 60 to 100 feet (18–30 m) in width, and was fordable in places and crossed by three stone bridges each a mile (1.5 km) apart. It was also a precarious position because the Confederate rear was blocked by the Potomac River and only a single crossing point, Boteler's Ford at Shepherdstown, was nearby should retreat be necessary. (The ford at Williamsport, Maryland, was 10 miles (16 km) northwest from Sharpsburg and had been used by Jackson in his march to Harpers Ferry. The disposition of Union forces during the battle made it impractical to consider retreating in that direction.) And on September 15, the force under Lee's immediate command consisted of no more than 18,000 men, only a third the size of the Federal army.

The first two Union divisions arrived on the afternoon of September 15 and the bulk of the remainder of the army late that evening. Although an immediate Union attack on the morning of September 16 would have had an overwhelming advantage in numbers, McClellan's trademark caution and his belief that Lee had as many as 100,000 men at Sharpsburg caused him to delay his attack for a day. This gave the Confederates more time to prepare defensive positions and allowed Longstreet's corps to arrive from Hagerstown and Jackson's corps, minus A.P. Hill's division, to arrive from Harpers Ferry. Jackson defended the left (northern) flank, anchored on the Potomac, Longstreet the right (southern) flank, anchored on the Antietam, a line that was about 4 miles (6 km) long. (As the battle progressed and Lee shifted units, these corps boundaries overlapped considerably.)

On the evening of September 16, McClellan ordered Hooker's I Corps to cross Antietam Creek and probe the enemy positions. Meade's division cautiously attacked Hood's troops near the East Woods. After darkness fell, artillery fire continued as McClellan positioned his troops for the next day's fighting. McClellan's plan was to overwhelm the enemy's left flank. He arrived at this decision because of the configuration of bridges over the Antietam. The lower bridge (which would soon be named Burnside Bridge) was dominated by Confederate positions on the bluffs overlooking it. The middle bridge, on the road from Boonsboro, was subject to artillery fire from the heights near Sharpsburg. But the upper bridge was 2 miles (3 km) east of the Confederate guns and could be crossed safely. McClellan planned to commit more than half his army to the assault, starting with two corps, supported by a third, and if necessary a fourth. He intended to launch a simultaneous diversionary attack against the Confederate right with a fifth corps, and he was prepared to strike the center with his reserves if either attack succeeded. The skirmish in the East Woods served to signal McClellan's intentions to Lee, who prepared his defenses accordingly. He shifted men to his left flank and sent urgent messages to his two commanders who had not yet arrived on the battlefield: Lafayette McLaws with two divisions and A.P. Hill with one division.

Terrain and its consequences

McClellan's plans were ill-coordinated and were executed poorly. He issued to each of his subordinate commanders only the orders for his own corps, not general orders describing the entire battle plan. The terrain of the battlefield made it difficult for those commanders to monitor events outside of their sectors. Moreover, McClellan's headquarters were more than a mile in the rear (at the Philip Pry house, east of the creek). This made it difficult for him to control the separate corps. This is why the battle progressed the next day as essentially three separate, mostly uncoordinated battles: morning in the northern end of the battlefield, midday in the center, and afternoon in the south. This lack of coordination and concentration of McClellan's forces almost completely nullified the two-to-one advantage the Union enjoyed. It also allowed Lee to shift his defensive forces to meet each offensive.

Battle

Morning phase

The battle opened at dawn (about 5:30 a.m.) on September 17 with an attack down the Hagerstown Turnpike by the Union I Corps under Joseph Hooker. Hooker's objective was the plateau on which sat the Dunker Church, a modest whitewashed building belonging to a congregation of German Baptist Brethren. Hooker had approximately 8,600 men, little more than the 7,700 defenders under Stonewall Jackson, and this slight disparity was more than offset by the Confederates' strong defensive positions. Abner Doubleday's division moved on Hooker's right, James Ricketts's moved on the left into the East Woods, and George Meade's Pennsylvania Reserves division deployed in the center and slightly to the rear. Jackson's defense consisted of the divisions under Alexander Lawton and John R. Jones in line from the West Woods, across the Turnpike, and along the southern end of Miller's Cornfield. Four brigades were held in reserve inside the West Woods.

As the first Union men emerged from the North Woods and into the Cornfield, an artillery duel erupted. Confederate fire was from the horse artillery batteries under Jeb Stuart to the west and four batteries under Colonel Stephen D. Lee on the high ground across the pike from the Dunker Church to the south. Union return fire was from nine batteries on the ridge behind the North Woods and twenty 20-pounder Parrott rifles, 2 miles (3 km) east of Antietam Creek. The conflagration caused heavy casualties on both sides and was described by Colonel Lee as "artillery Hell."

Seeing the glint of Confederate bayonets concealed in the Cornfield, Hooker halted his infantry and brought up four batteries of artillery, which fired shell and canister over the heads of the Federal infantry into the field. A battle began, with considerable melee action with rifle butts and bayonets due to short visibility in the corn. Officers rode about cursing and yelling orders no one could hear in the noise. Rifles became hot and fouled from too much firing; the air was filled with a hail of bullets and shells.

Meade's 1st Brigade of Pennsylvanians, under Brigadier General Truman Seymour, began advancing through the East Woods and exchanged fire with Colonel James Walker's brigade of Alabama, Georgia, and North Carolina troops. As Walker's men forced Seymour's back, aided by Lee's artillery fire, Ricketts's division entered the Cornfield, also to be torn up by artillery. Brigadier General Abram Duryée's brigade marched directly into volleys from Colonel Marcellus Douglass's Georgia brigade. Enduring heavy fire from a range of 250 yards (230 m) and gaining no advantage because of a lack of reinforcements, Duryée ordered a withdrawal.

Midday phase

By midday, the action had shifted to the center of the Confederate line. Sumner had accompanied the morning attack of Sedgwick's division, but another of his divisions, under French, lost contact with Sumner and Sedgwick and inexplicably headed south. Eager for an opportunity to see combat, French found skirmishers in his path and ordered his men forward. By this time, Sumner's aide (and son) located French, described the terrible fighting in the West Woods and relayed an order for him to divert Confederate attention by attacking their center.

French confronted D.H. Hill's division. Hill commanded about 2,500 men, less than half the number under French, and three of his five brigades had been torn up during the morning combat. This sector of Longstreet's line was theoretically the weakest. Hill's men, however, were in a strong defensive position, atop a gradual ridge, in a sunken road worn down by years of wagon traffic, which formed a natural trench.

French launched a series of brigade-sized assaults against Hill's improvised breastworks at around 9:30 a.m.. The first brigade to attack, mostly inexperienced troops commanded by Brigadier General Max Weber, was quickly cut down by heavy rifle fire; neither side deployed artillery at this point. The second attack, more raw recruits under Colonel Dwight Morris, was also subjected to heavy fire, but managed to beat back a counterattack by the Alabama Brigade of Robert Rodes. The third, under Brigadier General Nathan Kimball, included three veteran regiments, but they also fell to fire from the sunken road. French's division suffered 1,750 casualties (of his 5,700 men) in under an hour.

Reinforcements were arriving on both sides, and by 10:30 a.m. Robert E. Lee sent his final reserve division—some 3,400 men under Major General Richard H. Anderson—to bolster Hill's line and extend it to the right, preparing an attack that would envelop French's left flank. But at the same time, the 4,000 men of Major General Israel B. Richardson's division arrived on French's left. This was the last of Sumner's three divisions, which had been held up in the rear by McClellan as he organized his reserve forces.

Leading off the fourth attack of the day against the sunken road was the Irish Brigade of Brigadier General Thomas F. Meagher. As they advanced with emerald green flags snapping in the breeze, a regimental chaplain, Father William Corby, rode back and forth across the front of the formation shouting words of conditional absolution prescribed by the Roman Catholic Church for those who were about to die. The mostly Irish immigrants lost 540 men to heavy volleys before they were ordered to withdraw.

Afternoon phase

The action moved to the southern end of the battlefield. McClellan's plan called for Major General Ambrose Burnside and the IX Corps to conduct a diversionary attack in support of Hooker's I Corps, hoping to draw Confederate attention away from the intended main attack in the north. However, Burnside was instructed to wait for explicit orders before launching his attack, and those orders did not reach him until 10 a.m. Burnside was largely passive during preparations for the battle. The IX Corps had a clumsy command structure - Burnside had earlier commanded one wing of the Union army, composed of the I and IX Corps. Despite the I Corps being detached from Burnside's control, he still acted as if he were a wing commander. Orders for the IX Corps went to Burnside, who then passed them on directly to Jacob Cox. Cox had assumed temporary command of the corps after the death of Reno at South Mountain.

Burnside had four divisions (12,500 troops) and 50 guns east of Antietam Creek. Facing him was a force that had been greatly depleted by Lee's movement of units to bolster the Confederate left flank. At dawn, the divisions of Brig. Gens. David R. Jones and John G. Walker stood in defense, but by 10 a.m. all of Walker's men and Colonel George T. Anderson's Georgia brigade had been removed. Jones had only about 3,000 men and 12 guns available to meet Burnside. Four thin brigades guarded the ridges near Sharpsburg, primarily a low plateau known as Cemetery Hill. The remaining 400 men—the 2nd and 20th Georgia regiments, under the command of Brigadier General Robert Toombs, with two artillery batteries—defended Rohrbach's Bridge, a three-span, 125-foot (38 m) stone structure that was the southernmost crossing of the Antietam. It would become known to history as Burnside's Bridge because of the notoriety of the coming battle. The bridge was a difficult objective. The main road leading to it was exposed to enemy fire, but a farm lane allowed a more protected approach to around 250 yards (230 m) from the bridge. The bridge was dominated by a steep bluff on the west bank, and trees and an old quarry provided cover for defenders. The Confederates also strengthened their position with breastworks made from logs and fence rails.

Historians question why Burnside spent so much time at the bridge on Antietam Creek when the creek could have been forded "at a variety of places out of enemy range". The commanding terrain across the sometimes shallow creek made crossing the water a comparatively easy part of a difficult problem. Burnside concentrated his plan instead on storming the bridge while simultaneously crossing a ford McClellan's engineers had identified a half mile (1 km) downstream, but when Burnside's men reached it, they found the banks too high to negotiate. While Colonel George Crook's Ohio brigade prepared to attack the bridge with the support of Brigadier General Samuel Sturgis's division, the rest of the Kanawha Division and Brigadier General Isaac Rodman's division struggled through thick brush trying to locate Snavely's Ford, 2 miles (3 km) downstream, intending to flank the Confederates.

Aftermath

Casualties

The battle was over by 5:30 p.m. On the morning of September 18, Lee's army prepared to defend against a Federal assault that never came. After an improvised truce for both sides to recover and exchange their wounded, Lee's forces began withdrawing across the Potomac that evening to return to Virginia. Losses from the battle were heavy on both sides. The Union had 12,410 casualties with 2,108 dead. Confederate casualties were 10,316 with 1,547 dead. This represented 25% of the Federal force and 31% of the Confederates. Overall, both sides lost a combined total of 22,727 casualties in a single day, almost the same amount as the number of losses that had shocked the nation at the two-day Battle of Shiloh five months earlier.

Several generals died as a result of the battle, including major generals Joseph K. Mansfield and Israel B. Richardson and Brigadier General Isaac P. Rodman on the Union side, and brigadier generals Lawrence O. Branch and William E. Starke on the Confederate side. Confederate Brigadier General George B. Anderson was shot in the ankle during the defense of the Bloody Lane. He survived the battle but died later in October after an amputation. Six generals on each side were wounded. All were brigadiers except Union Major General Hooker and Confederate Major General Richard H. Anderson.

Antietam saw the most casualties for a single-day battle during the war, and has been described as the bloodiest day in all of American history. The battle ranks in the top ten in terms of total casualties in American Civil War battles. One source has the battle ranked fifth, falling behind Gettysburg, Chickamauga, Chancellorsville, and Spotsylvania Court House. Another source ranks Antietam eighth with the additional battles of the Wilderness, Shiloh, and Stones River ranked higher. Among those assisting the undersupplied army surgeons during (and after) the battle was Clara Barton, who brought a wagonload of medical supplies to the battlefield. She later founded the American Red Cross disaster relief organization.

Reactions and significance

President Lincoln was disappointed in McClellan's performance. He believed that McClellan's overly cautious and poorly coordinated actions in the field had forced the battle to a draw rather than a crippling Confederate defeat. The president was even more astonished that from September 17 to October 26, despite repeated entreaties from the War Department and the president himself, McClellan declined to pursue Lee across the Potomac, citing shortages of equipment and the fear of overextending his forces. General-in-Chief Henry W. Halleck wrote in his official report, "The long inactivity of so large an army in the face of a defeated foe, and during the most favorable season for rapid movements and a vigorous campaign, was a matter of great disappointment and regret." Lincoln relieved McClellan of his command of the Army of the Potomac on November 5, effectively ending the general's military career. He was replaced on November 9 by General Burnside.

Casualties were comparable on both sides, although Lee lost a higher percentage of his army. While Lee had successfully held off repeated Union assaults, he withdrew from the battlefield first, the technical definition of the tactical loser in a Civil War battle. In a strategic sense, despite being a tactical draw, Antietam is considered a turning point of the war and a victory for the Union because it ended Lee's strategic campaign (his first invasion of Union territory). American historian James M. McPherson summed up the importance of the Battle of Antietam in his book, Crossroads of Freedom:

No other campaign and battle in the war had such momentous, multiple consequences as Antietam. In July 1863 the dual Union triumphs at Gettysburg and Vicksburg struck another blow that blunted a renewed Confederate offensive in the East and cut off the western third of the Confederacy from the rest. In September 1864 Sherman's capture of Atlanta electrified the North and set the stage for the final drive to Union victory. These also were pivotal moments. But they would never have happened if the triple Confederate offensives in Mississippi, Kentucky, and most of all Maryland had not been defeated in the fall of 1862.

The results of Antietam were also politically magnified since the battle's outcome allowed President Lincoln to issue the preliminary Emancipation Proclamation on September 22, which gave Confederate states until January 1, 1863, to end their rebellion or else lose their slaves. Although Lincoln had intended to do so earlier, Secretary of State William H. Seward, at a cabinet meeting, advised him to wait until the Union won a significant victory so as to avoid the perception that it was issued out of desperation.

Battlefield preservation

The battle is commemorated at Antietam National Battlefield. Conservation work undertaken by Antietam National Battlefield and private groups, has earned Antietam a reputation as one of the nation's best preserved Civil War battlefields. Few visual intrusions mar the landscape, letting visitors experience the site nearly as it was in 1862.

Antietam was one of the first five Civil War battlefields preserved federally, receiving that distinction on August 30, 1890. Over 300 tablets have been placed to mark the spots of individual regiments and of significant phases in the battle. The battlefield was transferred to the Department of the Interior in 1933. The Antietam National Battlefield now consists of approximately 3,000 acres.

The American Battlefield Trust and its partners have acquired and preserved 488 acres of the Antietam Battlefield as of January 2024. In 2015, the Trust saved 44.4 acres in the heart of the battlefield, between the Cornfield and the Dunker Church, when it purchased the Wilson farm for about $1 million. The preservation organization has since removed the postwar house and barn that stood on the property along Hagerstown Pike and returned the land to its wartime appearance.