Antietam - The Bloodiest Day


By Paul Williams

In September 1862, despite having just beaten the Union army at the second battle of Bull Run, Lee knew the Confederacy faced a problem. After 18 months of war, despite winning a series of victories, the southern states remained isolated with neither Britain nor France wiling to give them diplomatic recognition. Virginia itself was exhausted and unlikely to be able to supply further campaigns. The only positive factor was the Union commander, George McLellan, who experience had shown to be cautious to the point of inertia.

To address this, Lee came up with a bold plan to take the war to the Union, launching an invasion of Maryland and threatening Washington itself. This would force McLellan to move north-east to protect the capital, giving Lee time to gather much needed supplies before heading west to the Shenandoah Valley and bringing the Union to battle on ground of his choosing. As well as boosting southern morale, a major victory might persuade the European powers to recognize the CSA and bring Washington to the negotiating table.


On Thursday September 4th, the Army of Virginia crossed the Potomac and headed north for the town of Frederick. From there, Lee intended to split his forces, Longstreet heading northwest into Pennsylvania while the bulk of the army moved to eliminate the Union garrisons at Martinsburg and Harpers Ferry that were blocking his intended supply route back to Virginia.

On Wednesday 10th, Lee’s forces moved from Frederick, Longstreet heading towards Pennsylvania with 3 divisions while the remaining 6 divisions moved to encircle Harpers Ferry.

Lee believed that McLellan would not be ready to advance against him for 3-4 weeks, giving him the time needed to open the supply route, send much needed supplies south and re-unite his forces. However, as soon as reports arrived of Lee’s advance, McLellan issued orders to move north to cover Washington.

On Friday 5th six corps began the march to Frederick, two corps remaining to protect against further confederate attacks. Although McLellan was still unsure of Lee’s plans, his forces continued north, reaching Frederick on Friday 12th.

Harpers Ferry must hold

In a stroke of luck, Union troops searching the abandoned Confederate camp discovered a copy of Lee’s campaign orders, wrapped around a pack of three cigars. On receipt of the orders, McClellan declared “Here is a paper with which if I cannot whip Bobby Lee, I will be willing to go home”. Provided the garrison at Harpers Ferry could hold out for a few daysMcLellancouldmanoeuvrehis forces west across the Catoctin and South Mountains and destroy the separate pieces of Lee’s army individually before they could unite.

At Harpers Ferry, although the garrison commander Col. Miles knew the rebels were on their way he convinced himself that they would attack from the west and concentrated his forces to meet that threat, ignoring the high ground that surrounded the town on all sides.

Late on Friday 12th the first Confederate forces under McClaws approached Harpers Ferry from the north and finding the hills virtually undefended occupied the high ground to the north and east. The next day, Walker and Jackson arrived and completed the encirclement of the town.

So far, Lee was unaware of McLellan’s approach but on Sunday 14th he received intelligence that Union forces had been spotted heading for Turner’s Gap at South Mountain. Immediately he ordered Longstreet and Hill to move to reinforce the units covering the gap and sent word to Jackson to take Harpers Ferry as quickly as possible and then move to rejoin the army.

First encounters – South Mountain

During the morning of Sunday 14th, the first Union troops approached Turner’s gap at South Mountain. Despite initial success, the arrival of reinforcements from Hill’s divisions prevented a breakthrough. Meanwhile, at Fox’s gap the defenders were brushed aside and Union forces moved to turn the Confederate flank at Turner’s gap. Once again Confederate reinforcements under Longstreet arrived in time to prevent a breakthrough. Finally, at 4pm, Union reinforcements broke through the Confederate lines and took Turner’s gap, opening the way through South Mountain, but then halted as darkness fell.

Meanwhile, to the south, Franklin moved to clear Crampton’s Gap, en route to Harpers Ferry but despite breaking through, paused for the night six miles from their objective.

At the Ferry, having received orders from Lee, Jackson began bombarding the town in preparation for an assault. Despite stating that he could hold for 48 hours, Col. Miles lost his nerve and the garrison was ordered to surrender. Jackson immediately paroled the garrison and started the move back to rejoin Lee.

Having lost the passes, Lee was concerned about having to fight with only two thirds of is army and was preparing to order a retreat back to Virginia when word came of the Union surrender. Lee immediately ordered his troops to concentrate at Sharpsburg ready for battle.

An opportunity lost – the Union wait

On Monday 15th and Tuesday 16th , despite having cleared the passes, McLellan spent the day re-organisinghis commands and deciding a plan of attack. Given Lee’s position the main assault by four corps’ was to be against the left flank to try and push Lee back and trap him against the Potomac. A fifth corps would mount a diversionary attack on the other flank while the sixth corps would form a central reserve.

At this stage, McLellan had the advantage, with 50,000 troops against Lee’s 20,000 but the delays allowed Jackson to rejoin Lee and bring the Confederate forces up to 38,000 men. In the only action, late on the 16th, Hooker’s I corps crossed the Antietam creek in readiness for their attack the next day, giving Lee time to realign his left flank to face the Union forces.

Phase 1:Dunkers Church and the Cornfield

At 05:30 on Wednesday September 17th the battle started with Hooker’s I Corps advancing towards Dunkers Church. As the troops advanced, they encountered stiff confederate resistance from a large cornfield but with the assistance of artillery, by 6:45 had cleared the cornfield and were on the verge of breaking through the Confederate flank. Fortuitously, Lee had moved Hood’s Texan brigade to meet the Union threat and at 7 am, they launched a furious counter-charge forcing I Corps back through the cornfield to their original position.

Although Hood’s troops continued to press forward, they were forced to halt their advance when confronted by reinforcements from Mansfield’s XII Corps brought up to support Hooker.

For two hours the battle raged back and forth with both sides feeding in additional troops as required and it was estimated afterwards that the cornfield had been taken and lost at least 15 times. Meanwhile, on the Union left flank, General Greene from XII Corps had managed to break through the line in the East Woods and take Dunkers Church but was unable to press forward beyond this point.

Finally, with the Confederates still holding the west woods, I Corps badly mauled and XII Corps totally disorganized, by 9am the fighting died down with approximately 4,000 casualties on each side but no clear victor.

Phase 2: Sumner’s Advance

To the south of Mansfield’s forces, Sumner’s II Corps had been awaiting orders to advance and support the ongoing attack around Dunker’s church. When these finally arrived at 7:30am, two divisions started to advance but it was not until 9am that Sedgwick’s division of 5,400 men was able to start its attack, by which time the Confederates had stopped the initial assault and were able to move troops across to meet the new threat.  

Advancing in a compact linear formation, the Union division was unable to react when attacked from three sides by Early, Walker and McClaw’s divisions and having suffered over 2,000 casualties in less than 30 minutes was forced to retreat.

Meanwhile, French’s division, which was meant to accompany Sedgwick into the attack, had lost contact and headed south towards the centre of the Confederate line. Facing French was D H Hills division which, despite having taken casualties during the earlier action was strongly entrenched in a sunken road.

At 9:30am, French began a series of brigade sized assaults against the Confederate position but despite three separate attacks, the Union were unable to break through, suffering 1,750 casualties in under an hour.

On both sides reinforcements were sent to the area, Lee committing his last reserve, the 3,400 men of Anderson’s division, while the 4,000 men of Richardson’s division moved to support French.

Arriving first, Richardson launched a fresh assault on the Confederate line lead by Meagher’s Irish Brigade. Although this assault initially failed, Caldwell’s brigade, moving forward in support, spotted a weak point in the Confederate line, a small knoll which allowed them to enfilade the sunken lane, turning it from a fortress into a trap.

As Confederate units attempted to maneuver to meet this new threat, Col. Lightfoot misinterpreted his orders to wheel and instead ordered his regiment to turn round and march to the rear. Believing that the same order also applied to them, five other regiments followed Lightfoot’s lead and withdrew from their position. Despite the arrival of Anderson’s division, the Confederate troops continued to retreat towards Sharpsburg leaving a massive gap in Lee’s centre.

Richardson attempted to exploit this gap, but his division was driven back by Confederate artillery and a counter-attack by D. H. Hill and was forced to take cover behind a ridge facing the sunken road.

Nearby, the 12,000 men of Franklin’s VI Corps had now arrived and were in a position to advance into the gap but Sumner as senior Corps’ commander ordered him to hold his position. Richardson appealed to the commander in chief but after listening to the arguments from both sides, McLellan agreed with Sumner and a second opportunity to break through the Confederate line was lost.

Between 9:30am and 1:00pm, the assaults on the sunken lane had cost 5,600 casualties including 2,600 Confederates and lead to the 700 metre long road being known as bloody lane.    

Phase 3: Burnside’s Bridge

Under McLellan’s original plan, Burnside’s IX Corps to the south of the line was meant to make a diversionary attack in support of the main assault by Hooker to pin down the Confederate troops covering Sharpsburg and prevent Lee from reinforcing his left flank.

However, despite being ready since dawn, Burnside had been instructed to await explicit orders before advancing and was forced to sit and do nothing while the battle erupted to hi north.

When the orders finally arrived at 10:00am the Confederate forces facing him had been severely depleted as Lee drew off units to face the Union threat in the north and centre of his line. To reach the rebel positions Burnside would have to cross the Antietam creek and, because of its proximity to Sharpsburg, Burnside chose to make his main assault via the southernmost of the three bridges, Rohrbach’s bridge, later renamed Burnside’s bridge.

Facing Burnside’s 11,000 men were a small force of 550 troops under General Toombs. Although grossly outnumbered they were positioned in 100 foot high bluffs with a clear view of the approach to the bridge and were well supported by artillery.

While a small Union force moved along the creek looking for a ford, the first assault was launched by Cook’s Ohio brigade but was soon pinned down by rebel fire and forced to withdraw. At 11am, a second brigade under Sturgis advanced in column of fours but under heavy rebel fire again failed to take the bridge. It was now 12am and increasingly urgent orders were despatched from McLellan's HQ urging Burnside to take the bridge regardless of cost.

For the 3rd assault, a brigade under Colonel Ferrero was ordered forward, supported by enfilade fire from two newly arrived batteries. With this additional support, and with the rebels running low on ammunition, at 1pm Toombs decided to withdraw his men to a new line half a mile back as the Federal troops finally began to cross the bridge.

Although the way now lay open for a full assault on Lee’s weakened centre, but any further advance was delayed as fresh units were brought up. By 2:30pm Burnside was finally ready to resume his advance but the delay had allowed Lee to move up A P Hill’s division, just arrived from Harper’s Ferry. Burnside managed to advance to within 200 yards of Sharpsburg, forcing the Confederates to abandon their position on Cemetery Hill, but at 3:30, 2,000 men from Hill’s division launched an attack on the Federal left flank and, despite still having more than twice as many troops as the Confederate, Burnside pulled his units back to the west bank of the Antietam creek.

Although beaten back, Burnside know that he still outnumbered the Confederate forces facing him and asked McLellan to send more men to mount a fresh assault and take Sharpsburg. Despite having both the V and VI Corps as yet uncommitted, McLellan had lost his nerve and refused to approve any reinforcements and at around 5:30 pm the guns fell silent.

The Aftermath

By the end of the battle it was estimated that both sides had suffered over 22,700 casualties, including around 3,650 men killed and a further 1,700 men missing, making it the bloodiest battle ever fought on American soil.

Despite the arrival of further reinforcements on the 18th, McLellan refused to renew the attack and that night the Confederate forces pulled out and began their march back to Virginia. On the 19th, discovering Lee has pulled out, McLellan despatched some cavalry and infantry to determine his location but, apart from sending troops to reoccupy Harpers Ferry, did nothing to pursue.

Despite McLellan’s failure to pursue Lee as his army withdrew, the battle was technically a strategic Union victory. This gave President Lincoln the positive circumstances he wanted in order to issue his emancipation proclamation which was duly published 7 days later.

By changing the tone of the war from a battle over state rights to a fight to free the southern slaves, the Union managed to switch opinion in both Britain and France, preventing the Confederacy from gaining the recognition and support they needed in order to hold off the Union forces and bring Lincoln to the negotiating table.

For McLellan, despite direct orders from Lincoln in early October to advance, he refused and it was not until October 26th that the vanguard of his army crossed the Potomac in pursuit of a now refreshed and reinforced Lee.

For Lincoln this was the final straw and on November 5th, orders were issued relieving McLelland and passing control of the army to General Burnside.

So who lost the battle?

Despite Lee making a series of tactical blunders in splitting his forces and being brought to battle with his back to the Potomac, the Union forces failed time and time again to exploit the opportunity through a series of failures by various commanders. Looking at the battle, there are a number of key points at which the Union let a decisive victory slip through their hands.

Firstly was the failure of Colonel Miles to adequately defend Harpers Ferry against Jackson, and of Franklin to advance to the garrisons relief on the 14th after clearing Crampton’s Gap. This failure allowed Jackson to parole the defenders and march back to rejoin Lee before the battle began, undermining McLellans plan to destroy the various elements of Lee’s force separately.

Secondly, there was McLellan’s decision to do nothing for two days after taking the mountain passes on the 14th. While a certain amount or re-organisation and planning was required following the day’s battles, Lee’s forces were still widely dispersed when the Union arrived and an attack on the forces in place at Sharpsburg on the 15th or even the 16th would have had a good chance of destroying half of Lee’s army before the forces from Harpers Ferry could return.

Thirdly, there was the delay in launching Burnside’s diversionary attack until 10am by which time the main assaults had largely been drive off with the help of reinforcements moved from the troops facing Burnside’s inactive command. If this attack had been launched at 7am or 8am, while the main attacks by Hooker and Sumner were underway, Lee would have been unable to withdraw forces and it is likley that the Confederate left flank would have given way, forcing Lee into a difficult fighting retreat with a river to his back.

Finally, there was the refusal of McLellan to commit additional troops to complete tactical victories, firstly by Franklin at 1pm in the centre, and secondly by Burnside at 5pm in the south. In both cases, McLellan had plenty of troops available to exploit the opportunity but, partly due to cautionary advice from his staff, chose not to act.

For Lee, Antietam was not his finest hour having originally divided his forces due to an underestimation of the speed with which the Union would react, and then found himself with his back to the river facing a vastly superior force, Luckily for him the Union command was not fit for purpose and with his instinct for how the battle was going Lee was able to switch his forces around to meet each attack and prevent a break through.

Unfortunately this was not enough for the Confederacy and despite the huge butchers bill on the day Antietam marked a significant turning point in the civil war. After Antietam and Lincoln’s subsequent emancipation proclamation the southern states would be unable to count on international recognition and while both sides would continue fighting for another two and a half years, the ultimate outcome was rarely in doubt.

Game Played by Paul Willaims and Stephen Dunn

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