CHAPTER 10

THE FORCES GATHER

SEPTEMBER 15–16, 1862

MCCLELLAN HAS BEEN ROUNDLY CRITICIZED BY HISTORIANS FOR his cautious handling of the opportunity presented by the finding of the lost order. He certainly failed to act as promptly and energetically as he could have. If McClellan had ordered Burnside and Franklin to march on the night of the thirteenth instead of the following morning, Franklin might have relieved Harpers Ferry, and McClellan’s column might have been able to attack and destroy Longstreet’s Divisions while they were marching up from Boonsboro. It could be argued, however, that McClellan’s caution was reasonable given his estimate of enemy strength, even if it is hard for historians who know how wrong McClellan was to accept that judgment.

As a matter of general principle, McClellan ought to have ordered the forward movement sooner and demanded more aggressive action by his front-line commanders. However, a swifter stronger offensive would probably not have produced the decisive results that historians have envisioned. Night marches were especially wearing on troops and tended to produce more than the usual amount of straggling. If Franklin had made his fourteen-mile march to Crampton’s Gap at night, he would have arrived at about 9:00AMwith his force diminished in numbers and physical stamina—to find J. E. B. Stuart’s two brigades of cavalry still in place, supporting McLaws’s infantry. Franklin’s troops would then have had a harder, longer, and costlier fight to clear Crampton’s Gap, and he would have faced the formidable task of storming the length of Elk Mountain with a weakened and weary force. By 4:00 PM on the fourteenth the Har­pers Ferry position was already indefensible, Colonel Miles had decided to surrender, and it is unlikely that an earlier start and a more aggressive drive by Franklin could have prevent Harpers Ferry’s fall.

The case is similar for McClellan’s northern column. An early-­morning breakthrough at Turner’s Gap would not have forced Longstreet to stand, fight, and be destroyed. Rather, it simply would have convinced Lee that he could not delay McClellan long enough for Jackson to rejoin him. He would have had little choice but to withdraw Longstreet’s infantry divisions via the Williamsport fords, following the wagon train and reserve artillery that were already withdrawing from Hagerstown. There was a risk that Hill’s Division would be badly mauled fighting as the rear guard, but the bulk of Lee’s detachment had plenty of time and space to make good its retreat.

Instead, the caution with which McClellan moved actually increased his odds of “bagging” Lee’s army. It tempted Lee to stay in the danger zone, in the hope that he could reunite his army in time to win the victory his strategy demanded. The process by which Lee succumbed to that temptation is a strange blend of tactical acumen, misunderstanding, and outrageous fortune.¹

SHARPSBURG

SEPTEMBER 15, 1862, MIDNIGHT TO NOON

Lee spent a sleepless night, riding in his ambulance from Boonsboro to Sharpsburg ahead of Longstreet’s retreat—an interminable stream of the ambulance trains, walking wounded, stragglers, and refugees from units wrecked or disorganized in the fighting. He issued a series of orders to ensure an orderly retreat to Virginia, among them several dispatches advising McLaws to make a prompt withdrawal northward from Maryland Heights, keeping Elk Mountain between his men and the enemy troops in Pleasant Valley, so that he might rejoin the main army at Sharpsburg,

Then, at 8:00 AM on September 15, Jackson’s dispatch, sent from Harpers Ferry the evening before, finally caught up with Lee. Jackson’s assurance that Harpers Ferry would fall that same day transformed the tactical situation. It might now be possible for Lee to reunite his army at Sharpsburg before McClellan could concentrate against him. Still, the conditions of battle would not be those he had hoped to create. Lee’s original plan called for his whole army to be concentrated west of South Mountain, rested, resupplied, and poised for rapid maneuver, to strike McClellan’s columns as they emerged from the narrow passes and tried to deploy in the Antietam valley. Now the units of Jackson’s force would have to scramble to get to Sharpsburg on time, while Lee would have to concede the initiative to McClellan and improvise a defensive battle plan. Still, the chief purpose of the campaign had been to inflict the most damaging blow possible on the morale and political solidarity of the North, and the only way to do that now was to meet McClellan’s army in battle and defeat it.

Orders went out to Longstreet and Hill to halt and take a defensive position at Sharpsburg, to McLaws and Jackson to come north and join them as soon after the surrender as possible. Then Lee rode out in his ambulance to survey the ground on which he would fight.

Sharpsburg was a small country town, a dozen square blocks of wood-frame houses on a plateau of rolling ground west of Antietam Creek. It was a junction where the roads from Hagerstown to the north and Boonsboro to the northeast met the roads running west to the Potomac crossings and south to the Harpers Ferry pontoon bridge. It was an obvious point of concentration for the troops retreating from Turner’s Gap and Hagerstown and for troops marching north from Harpers Ferry. It also offered a short and easy retreat via the Shepherdstown fords in case of defeat. The plateau was not sharply or steeply elevated above the valley of Antietam Creek, but it offered substantial advantages for an army on the defensive. There were only a few points by which an enemy approaching from the east could cross the creek, and most of these could be swept by artillery. The plateau was high enough to allow the defenders to see and fire on attacking columns as they advanced, and it was broken by thick woodlots, small rises of ground and sunken roads that offered the defenders concealment and protection from enemy fire.

Lee and his engineers sketched a compact arc of infantry and artillery positions, and as Longstreet’s troops reached Sharpsburg they took their designated places in the line. By 11:00 AM all of Hill’s and Longstreet’s troops were in position and had been joined by Colquitt’s Brigade and other units recalled from their duty of guarding fords or wagon trains. When stragglers from Hagerstown and Turner’s Gap came in, Lee would have between fifteen and eighteen thousand troops in line and—more significantly—over a hundred artillery pieces.

Although that line was thin and the reserves minimal, the position was a very strong one for the defense. Its right, or southern, flank was anchored on a high, steep ridge that overlooked the southernmost bridge over the Antietam. It appeared that this flank could only be turned by a frontal assault in overwhelming strength, something not likely to occur in the near term. The main line of defense ran north along a ridge of high ground, from which gunners could cover a Federal crossing by the Middle Bridge. The end of the ridge was marked by the Roulette Farm, and here the Confederate line was “refused,” or turned at a right angle, to defend against a Federal sweep around the northern flank.

Although there was no continuous ridgeline on this front, the ground still offered advantage to the defense. The cavalry division of Fitzhugh Lee held Nicodemus Hill, which was at the extreme left of the line, and close enough to the Potomac River to block an end run around that flank. “Fitz” Lee was a nephew of Robert E. Lee, a recently promoted Brigadier General at age twenty-seven, rated as one of Stuart’s most skilled subordinates.

Midway between Nicodemus Hill and the Roulette Farm was another hillock on which stood a little wooden church of the Dunker religious sect. This high ground was the central strongpoint of the north-facing Confederate line, and Lee posted several batteries of the reserve artillery force here to augment the defense’s firepower. The guns were commanded by Colonel Stephen D. Lee, a slender, dark-bearded twenty-nine-year-old South Carolinian whose abilities would eventually earn him command of an army.

The infantry line north of the Dunker Church was about two-thirds of a mile forward of Colonel Lee’s guns. It was anchored on the left in a long woodlot, known as the West Woods, and on the right by the smaller East Woods. Between these two woods was a broad swath of open ground, forming a natural corridor down which the Yankee attack was likely to come. The Hagerstown Pike ran down along the west side of this corridor, and much of the ground east of the pike was taken up by a large cornfield enclosed by a “worm fence”: a zigzag structure of long wooden rails laid between wooden crosspieces. A Federal column attacking down the pike would have to run a gauntlet of flank fire from the two woods, and frontal fire from infantry in the cornfield and the artillery posted at the church.

The Dunker Church could also be attacked by a force advancing down the Smoketown Road, a country lane that slanted down from the northeast to meet the Hagerstown Pike in front of it. But this road ran right through the East Woods, which would have to be cleared before an assault could be mounted from this direction.

The Confederate position as a whole formed a four-mile arc, running from the Rohrbach, or Lower, Bridge at the southern end to Nicodemus Hill at the northwestern extremity. The setup gave Lee the advantage of moving his reserves and shifting his troops along interior lines—shorter routes than those McClellan would have to use to go around the outside of the arc. While this tactical advantage offset somewhat the weakness of Lee’s infantry force, his chief reliance was in Jackson’s speed and McClellan’s sloth.²

At noon he received word from Jackson that Harpers Ferry was being surrendered.

HARPERS FERRY, DAWN TO NOON

Jackson had opened his batteries as soon as targets could be discerned through the light morning mist. Plunging fire from Maryland Heights hit the Federal infantry line that defended the town side of the pontoon bridge. Bolivar Heights was raked from the rear by Walker’s guns on Loudon Heights and heavy bombardment on the front and flank from Jackson’s artillery. Federal gunners replied sporadically and ineffectively, but mostly huddled in their entrenchments along with the infantry. Below Bolivar Heights Jackson’s infantry was slowly clawing its way through the abatis. But the artillery dominated the field, and after two hours of bombardment Colonel Miles concluded that honor had been served. A rider with a white flag showed himself on the ridgeline and the ceasefire call ran left and right along Jackson’s front. Some of his artillerymen decided to unload their pieces by firing a last shot at the Yankees. One of these exploded next to Colonel Miles, ripping a deep wound in his leg. He was carried to a hospital, where he would die the next day. In his stead, General White, who had abnegated his rank to subordinate himself to Miles, surrendered the post.

The Union troops were disgusted and humiliated rather than demoralized by their situation. Most felt they had not been beaten in a fair fight but let down by the military nincompoops who had commanded them. They passed disparaging remarks about the ragged, filthy, and hungry Rebel soldiers who looted their camps. Then General Jackson rode by in his scruffy rumpled uniform: “Boys,” said one Federal soldier, “he isn’t much to look at, but if we’d had him we wouldn’t have been caught in this trap.”³

However, Jackson and his men still had a great deal of work to do if the Rebels were going to realize the fruits of the victory. There were 11,300 Federal soldiers who had to be paraded, disarmed, counted, and lined up to sign the parole papers that would forbid their fighting or aiding their own army in any way until they were properly exchanged for Confederate prisoners or parolees. Soldiers on both sides were, in general, scrupulous in observing the terms of their parole.

Then the surrendered troops had to be mustered under guard, supplied with rations, and marched off without interfering with Confederate operations. While that was going on Confederate units had to be detailed to occupy the town and to secure the captured supplies to prevent or at least limit the spontaneous looting that always broke out whenever these chronically underfed and ill-clothed troops seized a Federal depot. The captured matériel—clothes and shoes, weapons and ammunition, food and forage—had to be sorted and piled, and Jackson’s officers had to organize a system for distributing the goods where they were most needed. Thousands of men needed new footgear or replacement for worn-out clothing, regiments armed with smoothbore muskets (or not armed at all) had to be reequipped with Yankee rifles. Everyone was ravenously hungry. The army had been on field rations since early August, a lean diet even when the rations were delivered, which they often were not. The green fruit and uncooked corn they had eaten in Maryland had not slaked their hunger and had played havoc with their bowels.

Jackson sent a dispatch to notify Lee of his triumph and to ask whether Lee wished him to rush as many troops as possible immediately to Sharpsburg. Assuming Lee did want that reinforcement, Jackson proposed leaving A. P. Hill’s Light Division behind to finish paroling the prisoners. Hill’s units had undertaken the hardest part of the siege operation, and most of Jackson’s two hundred casualties had come from Hill’s command. This was the dispatch Lee received at noon, some three hours after it was sent. He did not hesitate long. Although no copy survives of his response to Jackson, he evidently ordered Jackson to send all divisions but A. P. Hill’s to Sharpsburg as soon as possible. The two remaining divisions of Jackson’s Corps could march straight north and cross the Potomac by either the Shepherdstown or Boteler’s Ford. ­Walker’s Division would have to pass around or through Harpers Ferry to follow them. McLaws, however, was still in an awkward position, with the Federal VI Corps blocking the direct northern route through Pleasant Valley. He would have to disengage from those Federal troops and find another route to Sharpsburg. If these elements marched that afternoon, Lee thought they could be in Sharpsburg by nightfall. Since McClellan did not appear to be mounting a vigorous pursuit, Lee anticipated having most of his army concentrated to face McClellan in battle on September 16.⁴

LEE WAS RIGHT about the slow pace of McClellan’s advance, but he overestimated the speed and efficiency with which Jackson’s Divisions would move to his aid. The work of managing the surrender and resupplying his divisions proved tedious and time-consuming. It took most of the day before the divisions of Lawton and J. R. Jones disengaged from their fighting positions, resupplied with food and ordnance, and took the road northward. The weather was stiflingly hot and humid, and the men were dead tired. As part of Jackson’s command they had marched farther and harder than any units in the army. In addition to the two long flank marches they had made during the Second Bull Run campaign a month earlier, they had just completed a march of some seventy-five miles from Frederick to Harpers Ferry, crossing several high ridges and fording the Potomac in the process. They had been either marching or fighting every day since September 11. To get to Sharpsburg at daybreak on the sixteenth, they would have to make a grueling sixteen-mile night march that would leave them worn-out and weakened by straggling.

The commands of Walker and McLaws were also ordered to Sharpsburg on the fifteenth. They too had to dismantle their fighting positions on the heights, march down to the town for resupply, then work their way through the streets crowded by supply wagons, quartermaster details, and other units coming in for supply, to find their way north. McLaws’s command could not begin its movement until he was certain that the Federal corps in Pleasant Valley was not planning to assault his defense line on Elk Mountain. He had to disengage carefully, pull back along the rough terrain atop the ridge, then cross the pontoon bridge into Harpers Ferry before turning north behind Walker. As a result the divisions of Walker, Anderson, and McLaws would not be ready to march north till the morning of September 16. The only units from Harpers Ferry that arrived in time to take up fighting positions on the fifteenth were Stuart’s two cavalry brigades, which had missed the action at Crampton’s Gap.

On that same afternoon, McClellan’s infantry appeared in strength on the high ground east of Antietam Creek. Instead of having all but one of his divisions in line, as he had hoped, Lee had barely half of his army with him. Moreover, whether he knew it or not, the army itself had lost so heavily to straggling that its total strength was less than two-thirds what it had been at the start of the campaign. He ordered Longstreet to keep his skirmishers active, harassing the Union brigades as they took position. Longstreet had his artillery keep up sporadic but persistent firing, making great display of the number of batteries ranged all along the line. Longstreet had over a hundred guns, the normal complement for a much larger force than the eighteen thousand or so gathered around Sharpsburg, and they created an exaggerated impression of strength.

MCCLELLAN TRIUMPHANT

SEPTEMBER 15, MIDNIGHT TO 4:00 PM

McClellan knew he had won an important victory on September 14, but as dark closed down he was uncertain of its dimensions and consequences. At 9:40 PM he telegraphed Halleck, briefly characterizing the storming of Turners and Fox’s gaps. “It has been a glorious victory,” he concluded, but “I cannot yet tell whether the enemy will retreat during the night or appear in increased force in the morning.” It was possible that the gaps had been defended by a mere detachment and that the main body of Lee’s northern wing, which McClellan rated at forty to fifty thousand, was concentrating at Boonsboro for a counterstroke.⁵

He was up early on the morning of the fifteenth but remained at headquarters, where he could receive reports from Hooker, who was leading the advance force at Turner’s Gap, and from Franklin’s detachment at Crampton’s Gap. At 8:00 AM he was able to telegraph Halleck that Franklin had carried Crampton’s Gap “after a severe engagement,” and that the enemy on his own front had “disappeared during the night” and seemed to be retreating. He had ordered Franklin to pursue but did “not yet know where [the enemy] will next be found.” He clearly believed that the forces he had engaged on the fourteenth were “The Corps of D. H. Hill and Longstreet.” What is not clear is whether he literally supposed Hill’s command was a full army corps, or was using the term generically to refer to a substantial body of troops. It certainly would have been consistent with his estimate of Lee’s Boonsboro wing to rate Hill’s Division at double its actual strength.

Further reports from Hooker allowed him to telegraph Halleck at 8:30 AM that Lee’s force was in full retreat, “making for Shepherdstown in a perfect panic, & that Genl Lee last night stated publicly that he must admit they had been shockingly whipped.” It was information with no better authority than “some citizens from Boonsboro,” but McClellan was prepared to believe it. Shortly after this he received a report from one of his young staff officers, the dashing but not yet legendary Captain George Armstrong Custer, that Lee himself had been wounded in the action and D. H. Hill killed. The confusion was likely due to a civilian’s having seen Lee riding in an ambulance, because of the earlier injury to his hands; and there was a dead general, but it was Brigade Commander Garland, not D. H. Hill. Custer also reported a civilian’s statement that Lee had estimated his loss on the fourteenth as fifteen thousand troops. This was evidence of “a glorious & complete victory,” and McClellan was issuing orders for “hurrying everything forward to . . . press their retreat to the utmost.”⁶

For once, McClellan did seem actually to be hurrying. He ordered Hooker to lead the pursuit toward Boonsboro, with XII Corps following, and Burnside to clear IX Corps from the road so that fresh units from the II and V Corps could pass. After sending his last telegrams at 10:00 AM, McClellan would ride forward himself and discover that Burnside’s troops were just breaking camp, delaying the relief column. He impatiently ordered Burnside out of the way, and in his annoyance began entertaining doubts about his old friend’s military abilities.

At this point, McClellan was so enthusiastic about his prospects that he took time to send a personal telegram to Winfield Scott, informing his old commander that he had defeated a large enemy force, “occupying a strong mountain pass,” which was now “routed and retreating in disorder” with himself in close pursuit. He also wanted Scott to know that this “signal victory” had been won over an army with “R E Lee in command”—Lee, who had always been Scott’s favorite. To his wife he wrote, “If I can believe one tenth of what is reported, God has seldom given an army a greater victory than this.”

In fact, a substantial discount was warranted. Actual Confederate losses at South Mountain were about 2,300 out of 18,000 engaged, a rate of nearly 15 percent—a very serious loss to the northern wing of Lee’s army, which reduced its effective strength to approximately 15,000. If Lee had actually had the 40,000-plus troops with which McClellan credited him, a loss of 15,000 (upwards of 33 percent) would have been catastrophic. The passes through South Mountain would have been carpeted with bodies and the haul of prisoners in the thousands. McClellan could see for himself that this was not the case as he rode through the pass on the Boonsboro pike.⁷

It was risky to have exaggerated the scale of his victory as he had done. John Pope boasted of triumph, then saw himself discredited when Lee sprang his surprise assault on August 30; and, by McClellan’s estimate, Lee still had at least 35,000 troops, enough to cause problems for McClellan’s Corps as they filed through the gaps. Nevertheless, as he rode down from the hills on the road to Boonsboro he had reason to hope that he had indeed just fought and won the crucial battle of the campaign. Lee’s wing was evidently in full retreat, and, with Franklin poised to relieve Harpers Ferry, it seemed likely that Lee would have to abandon his invasion and return to Virginia. If that happened, McClellan would have met the fundamental requirement of his mission: to thwart the invasion of Maryland. He would have achieved that victory without running the risks or bearing the costs of a general engagement. By exaggerating the destruction inflicted on the enemy he magnified that achievement into something approaching a Napoleonic victory and anticipated the demand Lincoln was sure to make—that the enemy be destroyed or crippled by the defeat.

However, by early afternoon his situation began to seem more problematic. McClellan had been waiting to hear what progress Franklin was making in his attack against McLaws’s position on Elk Mountain. Shortly before noon he received a dispatch from Franklin, sent at 8:50 AM, reporting that firing could no longer be heard from Harpers Ferry, an indication that the post had surrendered. Franklin had not advanced against the Rebel troops in Elk Mountain and Pleasant Valley, and he wanted reinforcements. At about the same time, a report from Captain Custer indicated that Lee’s force was no longer retreating. It was drawn up in line of battle on high ground west of Antietam Creek, in front of the town of Sharpsburg. The line was “a perfect one about a mile and a half long. . . . Longstreet is in command and has forty cannon that we know of.” Custer was on higher ground east of the creek, from which most of the Antietam valley was visible. When General Hooker reached the same vantage point he thought the enemy force might be thirty to fifty thousand strong, with a hundred artillery pieces. He was right about the guns, but the haze of that hot and humid midday obscured his survey of the infantry positions, so that his estimate more than doubled Lee’s actual strength.⁸

It now appeared to McClellan that Lee’s army was not as demoralized as had been reported. If Hooker and Custer were right, it held a strong position, which it could defend until Jackson’s Corps, freed by the surrender of Harpers Ferry, could rejoin. With his army reunited, Lee could return to the offensive and attempt to complete what McClellan assumed was his strategic design for the conquest of Maryland. The “signal victory” at South Mountain would be valueless if McClellan could not compel Lee to retreat. But that would require another battle, most likely a general engagement to which the main force of the army would have to be committed.

That being the case, it would be best if McClellan could attack Lee’s detachment before Jackson’s troops rejoined. However, bringing his whole force to bear was not a simple task. Hooker had only two divisions fronting Sharpsburg. Before he could consider attacking the supposed thirty thousand to fifty thousand Confederates at Sharpsburg, McClellan had to assemble and properly organize a force of at least equal and preferably much greater strength. By McClellan’s own calculation, he had some thirty-eight thousand infantry in I and II Corps and Sykes’s Division who could reach the Antietam by early afternoon, in time to fight a battle. The XII Corps was still at Turner’s Gap and could not reach the Antietam till nightfall.

Burnside’s IX Corps, with about thirteen thousand infantry, was not far behind Hooker’s units—but at 3:45 PM McClellan felt compelled to divert its march. Now that the Rebels held Harpers Ferry, Jackson could throw most of his force into Pleasant Valley, smash through Franklin’s VI Corps, and threaten to take McClellan’s main force in the flank and rear, as he had done to Pope at Second Bull Run. Since McClellan credited Jackson with twice his actual force, such a menace seemed plausible. So McClellan ordered Burnside and IX Corps south to Rohrersville, at the northern end of Pleasant Valley, where it could go to Franklin’s aid if needed. McClellan would later reconsider that assignment and order Burnside to rejoin the main body, but IX Corps did not reach the hills above the Antietam until nightfall, too late to join in an attack.

McClellan rode ahead to join Hooker on the heights east of Antietam Creek. It was late afternoon on a parching hot day. Hooker’s troops were establishing positions on the slopes dropping down to the creek, and Confederate artillery was actively bombarding them. When McClellan’s large entourage emerged on the skyline, some of the fire was sent their way, so the general sent his staff to cover and made his telescopic survey of the enemy positions with a single aide. Heat haze, rolling terrain, and the large woodlots around Sharpsburg made it difficult to ascertain the exact size and positioning of the Rebel troops. However, from his vantage point McClellan could see that Lee’s forces were posted in strong positions on high ground west of the creek. There were three bridges across Antietam Creek, two of which were well covered by Confederate gunners. The Lower Bridge seemed to mark the southern flank of Lee’s position. There were high, steep, wooded hills immediately above it on the western bank, which made this an exceptionally strong defensive position. Federal troops advancing across the Middle Bridge would have to attack frontally across open ground against infantry and artillery on higher ground or in protected positions. It seemed a better idea to turn the Confederate position by crossing a strong force at the Upper Bridge and attacking Lee’s northern flank. However, with only forty thousand troops at hand McClellan did not have enough to hold Lee in front and at the same time swing a large force over the Upper Bridge to strike the flank.⁹

In fact, on the afternoon of September 15 Lee had fewer than half the troops with which McClellan credited him. McClellan and his colleagues were fooled, in part, because of their misguided assumptions about enemy strength, by the faulty system of intelligence gathering that supported those assumptions, and by the boldness of Lee’s decision to stand at Sharpsburg with such a small force. But they were also deceived by what they saw accurately enough: the number of regimental flags visible along the enemy line, and the number of guns firing from Rebel positions. Lee’s infantry regiments had been radically depleted by straggling, illness, and battle losses, but each still carried its flags, and Federal observers counting them from a distance could not tell whether they mustered fifty rifles or five hundred. Every brigade and division was assigned a certain number of artillery batteries, and these had not been reduced by straggling or battle loss. The divisions lined up across the Antietam still had their full complement of artillery, and Longstreet was advertising their presence by a program of active firing, which contributed to the impression that a solid corps of several divisions was making its stand and inviting attack.

McClellan therefore decided to postpone any offensive action until the following day, September 16, when he expected to have nearly his entire force concentrated against Sharpsburg.

BY FAILING TO ATTACK on September 15, McClellan lost an opportunity to ravage a major part of Lee’s army. The irony is that by declining to attack on that day, he also increased his chances for winning a major, perhaps even a decisive, victory.

McClellan had forty thousand troops at hand against the eighteen thousand under Lee and Longstreet. An all-out attack would likely have broken or compromised Lee’s defensive line and compelled his army to retreat—although such an outcome was far from certain, given the strength of Lee’s position and the quality of the force under his command. However, it is highly unlikely that an assault would have led to the destruction of that part of Lee’s army. An attack in sufficient strength could not have been launched until late in the day, by troops tired from long marches and (for I and IX Corps) a day of hard fighting. The Army of the Potomac had no doctrine for pursuit, and neither cavalry nor infantry was prepared for it. Lee would most probably have been able to save most of his infantry and artillery. It would have been a blow to Confederate prestige and to army morale for Lee’s force to have been driven from the field, though the capture of Harpers Ferry would have been some compensation. Nevertheless, such a defeat would not have “destroyed Lee’s army.” The eighteen thousand troops at risk represented about one-third of Lee’s present force but less than 15 percent of the Army of Northern Virginia’s reserve troop strength in the Virginia theater—enough of a reserve to enable Lee to reconstitute his army and effectively resist a Federal offensive.

The opportunity lost through McClellan’s unreasonable caution was restored by Lee’s unreasonable daring. Seeing the apparent hesitancy with which McClellan moved against him, Lee was tempted to risk Longstreet’s force for the chance to recover the initiative, reunite his army, defeat McClellan in battle, and complete the strategic design inherent in the invasion of Maryland. He held his eighteen thousand in place, spreading his depleted infantry to cover a position fit for an army, using his artillery aggressively, to bluff McClellan into delaying his attack.

But once again, McClellan’s unreasonable caution would lead him to miss his opportunity—and Lee’s unreasonable daring would hand it right back.

MCCLELLAN HESITATES, SEPTEMBER 16, 1862

On the morning of September 16, McClellan had almost all his force concentrated within easy supporting distance of the Antietam Creek position. Lee’s army was still divided, with most of Jackson’s wing at Harpers Ferry, seventeen miles away by the shortest marching route. Whether this position gave McClellan a tactical advantage or put his army in danger depended on the size of the two Confederate forces. Jackson’s was the wild card. From Harpers Ferry it could either march to join Lee, strike through Pleasant Valley to attack McClellan’s flank and communications, or attempt some combination of these two maneuvers. If Lee’s force was weak enough, an attack by McClellan’s available force might drive it from the field before Jackson could come to its aid; but if it was strong enough to hold its ground, Jackson’s arrival, especially if it took the form of a powerful flank attack, might catch McClellan’s army between anvil and hammer, as Pope had been caught. But how strong an attack could Jackson mount through Pleasant Valley? And how large a force would McClellan need to protect his flank? The answer to that last question would determine how much of his army McClellan could use against Lee on the sixteenth.

If McClellan’s estimates were accurate, on the fifteenth Lee and Longstreet had at least thirty thousand troops at Sharpsburg and Jackson between forty and fifty thousand at Harpers Ferry. McClellan thought he had about forty-five thousand troops immediately at hand with which to attack Lee. The army’s artillery reserve, with its batteries of powerful long-range guns, would come up early in the morning, and by noon would be positioned along the ridgeline east of Antietam Creek, firing to suppress the Rebel guns across the valley.¹⁰ There were also another fifteen thousand infantry marching down through the passes, but they would not reach the battlefield until late afternoon or early evening, too late to be useful in a general assault. Before McClellan could safely commit his main force to attack Lee, he had to ascertain where Jackson’s forces were, and how they were moving. Given McClellan’s estimate of Jackson’s strength, it was conceivable that overnight Jackson had sent Lee enough reinforcement to match McClellan’s forty-five thousand, while retaining enough strength at Harpers Ferry to attack Franklin’s nineteen thousand with superior forces.

In reality, only two of Jackson’s infantry divisions would reach Lee on September 16, footsore and weary after a night march, raising Confederate strength to about twenty-seven thousand. But that reinforcement merely doubled the stakes Lee had at risk. McClellan would have five of his six army corps concentrated on the high ground east of Antietam Creek, an effective strength of about sixty thousand augmented by an artillery arm that far outgunned and outranged its Confederate counterpart. Franklin’s VI Corps was still guarding Pleasant Valley but could have been called up in time to provide a defensive reserve. An all-out assault on the sixteenth would have had excellent chances of success, and the victors would have had a long, late-summer day in which to pursue a retreating enemy.

IT HAD RAINED during the night, and the heat of the new day brought up a heavy fog that cloaked the Confederate positions at Sharpsburg, frustrating McClellan’s attempts to inspect the Confederate lines through his telescope. The fog cleared after 9:00 AM, but the day remained hazy. From McClellan’s position it was impossible to tell whether Jackson was on the scene or still moving up over the road from Shepherdstown or Boteler’s Ford. To clarify the situation, McClellan had to probe the enemy positions by making limited attacks. But it was useless to probe the positions fronting Antietam Creek, where attackers had to cross open ground against lines well supplied with artillery.

The best option was to move against Lee’s northern flank, where the Rebel positions looked weaker and scattered woodlots would give the attackers cover in the advance and shelter in case of a reverse. However, to approach that flank, Federal troops had to cross the Antietam upstream and act separately from the rest of the army, where they could be cut off and destroyed by a Confederate concentration. So the force sent had to be large enough to stave off an attack by fifteen or twenty thousand Confederates.

After spending the morning considering his options, McClellan ordered Hooker to take I Corps, “cross the river . . . and attack the enemy on his left flank.” Hooker was not entirely happy with the assignment. His own survey of the Rebel positions on the fifteenth led him to believe Lee had at least thirty thousand on the scene, while his corps had, by his own estimate, only twelve or thirteen thousand with which “to attack the whole rebel army.” After giving his orders, he rode to McClellan’s headquarters to state his concerns. He was afraid “the rebels would eat me up” if McClellan did not divert Lee’s strength and attention by making “another attack . . . on the enemy’s right” or stand ready to send reinforcements “promptly” to his aid. McClellan reassured him that any call for reinforcements would be met and that any forces sent would be under Hooker’s command. This was not only a proper command arrangement for such an operation, it was a sop to Hooker’s notorious ambition for higher command. It implied that in conducting this operation he would not be subordinate to any of the other corps commanders, all of whom were senior to Hooker.

However, McClellan would give no orders for diversionary attacks against other parts of the Confederate line. Nor did he move any of the available II Corps divisions into positions from which they might have reinforced Hooker on September 16. Despite the fact that Hooker’s operation was originally styled an attack, it was in effect a reconnaissance-in-force, aimed at both establishing the location and strength of Lee’s northern flank and discovering whether Jackson’s reinforcement had arrived. With that information in hand, McClellan would know whether any part of VI Corps could be recalled from its watch on Pleasant Valley to augment the offensive against Sharpsburg.¹¹

Hooker got his orders just after 1:00 PM, but his advance was slow to develop. It took time for Hooker to give his orders, for his brigadiers to get their troops into marching order, cross the Antietam via the upper bridge and an adjacent ford, then deploy and begin the advance toward the enemy some four miles farther on. It was after 4:00 PM when his lead division made contact with the Confederate skirmish lines. Hooker pushed his divisions ahead until stiffening resistance revealed the Rebels’ main line of resistance in the woodlots and fields flanking the Hagerstown Pike. Hooker halted, established a defensive position for the night, and called for reinforcements. He had established that the Rebels’ northern flank ran along relatively higher ground for a mile and a quarter, from Nicodemus Hill on the east, through a large woodlot (the “West Woods”), across the north-south Hagerstown Pike to the Roulette Farm buildings a quarter mile west of the Pike. There was a half-mile gap between Nicodemus Hill and the Potomac River, but even with reinforcement Hooker’s line could not be extended far enough to turn that flank. Hooker could offer no information as to whether or not Jackson’s Corps was on the scene.

By the close of day on the sixteenth, reports from Franklin had given McClellan some assurance that there was no sign of a Confederate attack northward through Pleasant Valley. While that suggested that Jackson had sent most of his troops to Sharpsburg, it was less worrying to have Jackson in front than looming as a menace to his flank and rear. He therefore ordered Franklin to march at dawn and join him on the Antietam with his two VI Corps divisions. However, he remained concerned enough about a flank attack out of Harpers Ferry to order Couch’s newly arrived division to move south through Pleasant Valley, to develop any Rebel movement there and if possible seize Maryland Heights. He would also caution Burnside, whose IX Corps would form his left flank on the Antietam, to keep an eye out for a Confederate flanking column coming up from Harpers Ferry.

The delay further enabled McClellan to concentrate nearly his entire field force for the confrontation with Lee. The XII Corps, which arrived late in the evening, could be sent to support Hooker on the far side of the Antietam without weakening the main body. Franklin’s two divisions would arrive in the morning to form (with V Corps) a powerful reserve behind Sumner’s II Corps. Most importantly, McClellan and his staff would have time to properly position the powerful batteries of the army’s artillery reserve. In a clash between infantry armies of equal strength, artillery superiority could give the Army of the Potomac a crucial tactical edge. The basic principle was Napoleonic, and it was the core of McClellan’s tactical doctrine. In the Peninsula campaign he had planned to defeat an enemy of equal or superior infantry strength by deploying the huge heavy guns of the army’s siege train. While there were no siege guns with the artillery reserve at Antietam, the guns its batteries did deploy were twenty-pounder Parrott rifles and thirty-two-pounder howitzers, the heaviest field pieces used during the war, superior in range and in the weight and explosive power of their shot to anything in Lee’s artillery train. From the high ground east of the creek, where engineers had carefully emplaced them, their shell fire could hit anything on the battlefield that appeared in their line of sight.

Still, by postponing action until September 17 and allowing Jackson to reinforce Lee, McClellan lessened his chances of winning a decisive tactical victory, the kind that had seemed possible on September 13 as he studied General Order No. 191. As McClellan saw it, that opportunity had vanished when Lee escaped the pursuit after South Mountain and took his stand at Antietam. Nor was such a victory a strategic necessity. He had been restored to command at a moment of strategic crisis, with the army in disarray, the government deranged by the machinations of the Radicals, and the people demoralized. Here also was a large victorious Rebel army invading Northern territory, threatening to detach Maryland from the Union, while menacing Northern cities like Harrisburg, Baltimore, and Philadelphia. To bring this strategic crisis to a successful end and vindicate his status as the indispensable man, all he had to do was fight hard enough to compel Lee to retreat. That being the case, it was not only unnecessary but also unwise for him to run the risks entailed by any attempt to win a Napoleonic victory—for example, by hurling his available force at Lee on September 16. By delaying action he believed he minimized the odds that he might suffer a disastrous defeat. His army was concentrated so it could not be attacked in detail, and positioned so that it could not be easily or speedily outflanked. His artillery advantage made it possible for him to conduct a successful attack on Lee’s infantry line, and he had also hedged against the risk of a repulse by occupying a very strong defensive position. His high ground was higher than Lee’s and packed with artillery. McClellan would also have a substantial infantry reserve posted behind the center of his line, from which it could either exploit a breakthrough or backstop a retreat.

All of McClellan’s actions and refusals of action on September 16 were reasonable and prudent, given his assumptions about the strength and position of the enemy before him. The reality was that McClellan wasted September 16 maneuvering against phantoms. Jackson never intended to mount an offensive through Pleasant Valley, and lacked the strength to do so. His weary divisions had taken much longer to reach Sharpsburg, and arrived in far less strength, than either Lee or McClellan had expected. The divisions of Lawton and D. R. Jones had arrived at 6:00 AM but added only eight thousand troops to the nineteen thousand already in position there. Even without VI Corps, McClellan had more than sixty thousand troops against Lee’s twenty-seven thousand—a force more than ample for the tactics McClellan had in mind. He enjoyed the same two-to-one superiority he had had on September 15, but now he had two-thirds of Lee’s army in his grasp and hours of daylight in which to attack and pursue.

By failing to attack, McClellan missed his best opportunity to inflict a decisive defeat on Lee’s army at little cost to his own. His hesitation allowed Walker’s and McLaws’s Divisions to reach Sharpsburg before the fighting began, raising Lee’s force to roughly thirty-six thousand—only half of the seventy-two thousand McClellan would bring to the field, but still enough for Lee’s purposes.