Opposing forces Confederate Further information: Antietam Confederate order of battle General Lee's Army of Northern Virginia was organized into two large infantry corps.<8> The First Corps, under Maj. Gen. James Longstreet, consisted of the divisions of: * Maj. Gen. Lafayette McLaws (brigades of Brig. Gens. Joseph B. Kershaw, Howell Cobb, Paul J. Semmes, and William Barksdale). * Maj. Gen. Richard H. Anderson (brigades of Cols. Alfred Cumming, W.A. Parham, and Carnot Posey, and Brig. Gens. Lewis A. Armistead, Roger A. Pryor, and Ambrose R. Wright). * Brig. Gen. David R. Jones (brigades of Brig. Gens. Robert A. Toombs, Thomas F. Drayton, Richard B. Garnett, James L. Kemper, and Cols. Joseph T. Walker and George T. Anderson). * Brig. Gen. John G. Walker (brigades of Colonel Van H. Manning and Brig. Gen. Robert Ransom, Jr.). * Brig. Gen. John Bell Hood (brigades of Cols. William T. Wofford and Evander M. Law). * Independent brigade under Brig. Gen. Nathan G. "Shanks" Evans. The Second Corps, under Maj. Gen. Thomas J. "Stonewall" Jackson, consisted of the divisions of: * Brig. Gen. Alexander R. Lawton (brigades of Col. Marcellus Douglass, Brig. Gen. Jubal A. Early, Col. James A. Walker, and Brig. Gen. Harry T. Hays). * Maj. Gen. A.P. Hill (the Light Division — brigades of Brig. Gens. Lawrence O'Bryan Branch, Maxcy Gregg, James J. Archer, and William Dorsey Pender, and Cols. John M. Brockenbrough and Edward L. Thomas). * Brig. Gen. John R. Jones (brigades of Cols. A.J. Grigsby, E.T.H. Warren, Bradley T. Johnson, and Brig. Gen. William E. Starke). * Maj. Gen. D.H. Hill (brigades of Brig. Gens. Roswell S. Ripley, Robert E. Rodes, Samuel Garland, Jr., George B. Anderson, and Col. Alfred H. Colquitt). The remaining units were the Cavalry Corps, under Maj. Gen. J.E.B. Stuart, and the reserve artillery, commanded by Brig. Gen. William N. Pendleton. The Second Corps was organized with artillery attached to each division, in contrast to the First Corps, which reserved its artillery at the corps level.

Union Further information: Antietam Union order of battle Lincoln with McClellan and staff at the Grove Farm after the battle. Notable figures (from left) are 5. Alexander S. Webb, Chief of Staff, V Corps; 6. McClellan;. 8. Dr. Jonathan Letterman; 10. Lincoln; 11. Henry J. Hunt; 12. Fitz John Porter; 15. Andrew A. Humphreys; 16. Capt. George Armstrong Custer. Lincoln with McClellan and staff at the Grove Farm after the battle. Notable figures (from left) are 5. Alexander S. Webb, Chief of Staff, V Corps; 6. McClellan;. 8. Dr. Jonathan Letterman; 10. Lincoln; 11. Henry J. Hunt; 12. Fitz John Porter; 15. Andrew A. Humphreys; 16. Capt. George Armstrong Custer. Maj. Gen. George B. McClellan's Army of the Potomac, bolstered by units absorbed from John Pope's Army of Virginia, included six infantry corps.<9> The I Corps, under Maj. Gen. Joseph Hooker, consisted of the divisions of: * Brig. Gen. Rufus King (brigades of Col. Walter Phelps and Brig. Gens. Abner Doubleday, Marsena R. Patrick, and John Gibbon). * Brig. Gen. James B. Ricketts (brigades of Brig. Gen. Abram Duryée, Col. William A. Christian, and Brig. Gen. George L. Hartsuff). * Brig. Gen. George G. Meade (brigades of Brig. Gen. Truman Seymour and Col. Thomas F. Gallagher). The II Corps, under Maj. Gen. Edwin V. Sumner, consisted of the divisions of: * Maj. Gen. Israel B. Richardson (brigades of Brig. Gen. John C. Caldwell, Brig. Gen. Thomas F. Meagher, and Col. John R. Brooke). * Maj. Gen. John Sedgwick (brigades of Brig. Gens. Willis A. Gorman, Oliver O. Howard, and Napoleon J.T. Dana). * Brig. Gen. William H. French (brigades of Brig. Gen. Nathan Kimball, Col. Dwight Morris, and Brig. Gen. Max Weber). The V Corps, under Maj. Gen. Fitz John Porter, consisted of the divisions of: * Maj. Gen. George W. Morell (brigades of Col. James Barnes, Brig. Gen. Charles Griffin, and Col. T.B.W. Stockton). * Brig. Gen. George Sykes (brigades of Lt. Col. Robert C. Buchanan, Major Charles S. Lovell, and Col. Gouverneur K. Warren). * Brig. Gen. Andrew A. Humphreys (brigades of Brig. Gen. Erastus B. Tyler and Col. Peter H. Allabach). The VI Corps, under Maj. Gen. William B. Franklin, consisted of the divisions of: * Maj. Gen. Henry W. Slocum (brigades of Col. Alfred T.A. Torbert, Col. Joseph J. Bartlett, and Brig. Gen. John Newton). * Maj. Gen. William F. "Baldy" Smith (brigades of Brig. Gens. Winfield S. Hancock and William T. H. Brooks and Col. William H. Irwin). * A division from the IV Corps under Maj. Gen. Darius N. Couch (brigades of Brig. Gens. Charles Devens, Jr., Albion P. Howe, and John Cochran). The IX Corps, under Maj. Gen. Ambrose E. Burnside, consisted of the divisions of: * Brig. Gen. Orlando B. Willcox (brigades of Cols. Benjamin C. Christ and Thomas Welsh). * Brig. Gen. Samuel D. Sturgis (brigades of Brig. Gens. James Nagel and Edward Ferrero). * Brig. Gen. Isaac P. Rodman (brigades of Cols. Harrison S. Fairchild and Edward Harland). * Kanawha Division, under Brig. Gen. Jacob D. Cox (brigades of Cols. Hugh Ewing and George Crook). The XII Corps, under Maj. Gen. Joseph K. Mansfield, consisted of the divisions of: * Brig. Gen. Alpheus S. Williams (brigades of Brig. Gens. Samuel W. Crawford and George H. Gordon). * Brig. Gen. George S. Greene (brigades of Lt. Col. Hector Tyndale, Col. Henry J. Stainrook, and Col. William B. Goodrich). * Cavalry division of Brig. Gen. Alfred Pleasonton (brigades of Maj. Charles J. Whiting and Cols. John F. Farnsworth, Richard H. Rush, Andrew T. McReynolds, and Benjamin F. Davis).

Lincoln with McClellan and staff at the Grove Farm after the battle. Notable figures (from left) are 5. Alexander S. Webb, Chief of Staff, V Corps; 6. McClellan;. 8. Dr. Jonathan Letterman; 10. Lincoln; 11. Henry J. Hunt; 12. Fitz John Porter; 15. Andrew A. Humphreys; 16. Capt. George Armstrong Custer.

Battle Overview of the Battle of Antietam. Overview of the Battle of Antietam. 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, and 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.<10> 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 over 100,000 men 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.)

Overview of the Battle of Antietam.

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 the Confederates under Hood near the East Woods. After darkness, artillery fire continued as McClellan continued to position his troops. 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.<11> 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. 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, and McClellan's headquarters were more than a mile in the rear (at the Philip Pry house, east of the creek), making it difficult for him to control the separate corps. Therefore, the battle progressed the next day as essentially three separate, mostly uncoordinated battles: morning in the northern end of the battlefield, mid-day 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 and allowed Lee to shift his defensive forces to meet each offensive.

The Dunker Church at Antietam

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 the Dunker Church sat, a modest whitewashed building belonging to a local sect of German Baptists. 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.<12> 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 the Miller Cornfield. Four brigades were held in reserve inside the West Woods.<13> 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 Col. 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 four batteries of 20-pounder Parrott rifles, 2 miles (3 km) east of Antietam Creek. The conflagration caused heavy casualties on both sides and was described by Col. Lee as "artillery Hell."<14> 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, covering the field. The artillery and rifle fire from both sides acted like a scythe, cutting down cornstalks and men alike.

Assaults by the I Corps, 5:30 to 7:30 a.m.

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, covering the field. The artillery and rifle fire from both sides acted like a scythe, cutting down cornstalks and men alike.

Dead Confederate soldiers from Starke's Louisiana Brigade, on the Hagerstown Turnpike, north of the Dunker Church. Photograph by Gardner

Meade's 1st Brigade of Pennsylvanians, under Brig. Gen. 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. Brig. Gen. 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.<13> The reinforcements that Duryée had expected—brigades under Brig. Gen. George L. Hartsuff and Col. William A. Christian—had difficulties reaching the scene. Hartsuff was wounded by a shell, and Christian dismounted and fled to the rear in terror. When the men were rallied and advanced into the Cornfield, they met the same artillery and infantry fire as their predecessors. As the superior Union numbers began to tell, the Louisiana "Tiger" Brigade under Harry Hays entered the fray and forced the Union men back to the East Woods. The casualties received by the 12th Massachusetts Infantry, 67%, were the highest of any unit that day.<15> The Tigers were beaten back eventually when the Federals brought up a battery of 3-inch ordnance rifles and rolled them directly into the Cornfield, point-blank fire that slaughtered the Tigers, who lost 323 of their 500 men.<16> ...the most deadly fire of the war. Rifles are shot to pieces in the hands of the soldiers, canteens and haversacks are riddled with bullets, the dead and wounded go down in scores. Captain Benjamin F. Cook of the 12th Massachusetts Infantry, on the attack by the Louisiana Tigers at the Cornfield<17> While the Cornfield remained a bloody stalemate, Federal advances a few hundred yards to the west were more successful. Brig. Gen. John Gibbon's 4th Brigade of Doubleday's division (recently named the Iron Brigade) advanced down the turnpike, pushing aside Jackson's men. They were halted by a charge of 1,150 men from Starke's brigade, leveling heavy fire from 30 yards (30 m) away. The Confederate brigade withdrew after being exposed to fierce return fire from the Iron Brigade, and Starke was mortally wounded.<18> The Union advance on the Dunker Church resumed and cut a large gap in Jackson's defensive line, which teetered near collapse. Although the cost was steep, Hooker's corps was making steady progress. Confederate reinforcements arrived just after 7 a.m. The divisions under McLaws and Richard H. Anderson arrived following a night march from Harpers Ferry. Around 7:15, General Lee moved George T. Anderson's Georgia brigade from the right flank of the army to aid Jackson.

At 7 a.m., Hood's division of 2,300 men advanced through the West Woods and pushed the Union troops back through the Cornfield again. The Texans attacked with particular ferocity because as they were called from their reserve position they were forced to interrupt the first hot breakfast they had had in days. They were aided by three brigades of D.H. Hill's division arriving from the Mumma Farm, southeast of the Cornfield, and by Jubal Early's brigade, pushing through the West Woods from the Nicodemus Farm, where they had been supporting Jeb Stuart's horse artillery. Hood's men bore the brunt of the fighting, however, and paid a heavy price—60% casualties—but they were able to prevent the defensive line from crumbling and held off the I Corps. When asked by a fellow officer where his division was, Hood replied, "Dead on the field."<19> Hooker's men had also paid heavily but without achieving their objectives. After two hours and 2,500 casualties, they were back where they started. The Cornfield, an area about 250 yards (230 m) deep and 400 yards (400 m) wide, was a scene of indescribable destruction. It was estimated that the Cornfield changed hands no fewer than 15 times in the course of the morning.<20> Hooker called for support from the 7,200 men of Mansfield's XII Corps. ... every stalk of corn in the northern and greater part of the field was cut as closely as could have been done with a knife, and the slain lay in rows precisely as they had stood in their ranks a few moments before. Maj. Gen. Joseph Hooker<21> Assaults by the XII Corps, 7:30 to 9:00 a.m. Assaults by the XII Corps, 7:30 to 9:00 a.m. Half of Mansfield's men were raw recruits, and Mansfield was also inexperienced, having taken command only two days before. Although he was a veteran of 40 years' service, he had never led large numbers of soldiers in combat. Concerned that his men would bolt under fire, he marched them in a formation that was known as "column of companies, closed in mass," a bunched-up formation in which a regiment was arrayed ten ranks deep instead of the normal two. As his men entered the East Woods, they presented an excellent artillery target, "almost as good a target as a barn." Mansfield himself was felled by a sniper's bullet and died later in the day. Alpheus Williams assumed temporary command of the XII Corps.<22>

Assaults by the XII Corps, 7:30 to 9:00 a.m.

The new recruits of Mansfield's 1st Division made no progress against Hood's line, which was reinforced by D.H. Hill's divisions under Colquitt and McRae. The 2nd Division of the XII Corps, under George Sears Greene, however, broke through McRae's men, who fled under the mistaken belief that they were about to be trapped by a flanking attack. This breach of the line forced Hood and his men, outnumbered, to regroup in the West Woods, where they had started the day.<15> Greene was able to reach the Dunker Church, Hooker's original objective, and drove off Stephen Lee's batteries. Federal forces held most of the ground to the east of the turnpike. Hooker attempted to gather the scattered remnants of his I Corps to continue the assault, but a Confederate sharpshooter spotted the general's conspicuous white horse and shot Hooker through the foot. Command of his I Corps fell to General Meade, since Hooker's senior subordinate, James B. Ricketts, had also been wounded. But with Hooker removed from the field, there was no general left with the authority to rally the men of the I and XII Corps. Greene's men came under heavy fire from the West Woods and withdrew from the Dunker Church. In an effort to turn the Confederate left flank and relieve the pressure on Mansfield's men, Sumner's II Corps was ordered at 7:20 a.m. to send two divisions into battle. Sedgwick's division of 5,400 men was the first to ford the Antietam, and they entered the East Woods with the intention of turning left and forcing the Confederates south into the assault of Ambrose Burnside's IX Corps. But the plan went awry. They became separated from William H. French's division, and at 9 a.m. Sumner, who was accompanying the division, launched the attack with an unusual battle formation—the three brigades in three long lines, men side-by-side, with only 50 to 70 yards (60 m) separating the lines. They were assaulted first by Confederate artillery and then from three sides by the divisions of Early, Walker, and McLaws, and in less than half an hour Sedgwick's men were forced to retreat in great disorder to their starting point with over 2,200 casualties.<23> Sumner has been condemned by most historians for his "reckless" attack, his lack of coordination with the I and XII Corps headquarters, losing control of French's division when he accompanied Sedgwick's, failing to perform adequate reconnaissance prior to launching his attack, and selecting the unusual battle formation that was so effectively flanked by the Confederate counterattack. Historian M.V. Armstrong's recent scholarship, however, has determined that Sumner did perform appropriate reconnaissance and his decision to attack where he did was justified by the information available to him.<24> The final actions in the morning phase of the battle were around 10 a.m., when two regiments of the XII Corps advanced, only to be confronted by the division of John G. Walker, newly arrived from the Confederate right. They fought in the area between the Cornfield in the West Woods, but soon Walker's men were forced back by two brigades of Greene's division, and the Federal troops seized some ground in the West Woods. The morning phase ended with casualties on both sides of almost 13,000, including two Union corps commanders.<25> Mid-day