Criticism: The first two Union divisions arrived on the afternoon of September 15 with the bulk of the remainder late that evening. Although an immediate Union attack on the morning of September 16 would have enjoyed 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 until the next day. In fact, Lee had only 43,000. McClellan’s delay gave the Lee a full day to mass his forces and prepare defensive positions.
Response: This is a curious criticism. It is well known, and thoroughly documented, that McClellan did not launch his main assault on the morning of September 16 (1) because the ammunition trains were very late in arriving, (2) because there was a dense fog that lasted until around noon, and (3) because he had discovered that Lee had repositioned many of his units by the morning of the 16th and therefore McClellan naturally had to do more reconnaissance to determine Lee’s new positions and dispositions. No sensible commander would have launched his main assault until there was sufficient visibility and until he had a decent idea of the enemy’s new locations and dispositions.
Furthermore, McClellan did attack on the afternoon of the 16th. He did not launch his main assault until the following day, but he sent an entire corps forward on the Union right, across Antietam Creek, and in heavy fighting that lasted until dark that corps pushed the opposing Confederate force back to the Miller House.
The figure of 43,000 for Lee’s force is arguably off by at least 70%. Joseph Harsh and Gene Thorp, among other scholars, have made a strong case that Lee had closer to 75,000 troops at Antietam (see, for example, Harsh, Taken at the Flood: Robert E. Lee and Confederate Strategy in the Maryland Campaign of 1862, Kent State University Press, 1999, pp. 37-39). It has long been known that Confederate commanders would sometimes deliberately under-report their troop strength after a battle, especially if they lost the battle, so as to make their performance look better.
The traditional casualty numbers for Antietam also deserve another look. Most books on Antietam report that Lee’s total casualties were 10,320, as opposed to 12,400 for McClellan, with Lee suffering 1,500 killed, 7,750 wounded, and 1,020 missing or captured. But Civil War veteran and scholar Isaac Heysinger argued that Lee’s supposed casualty numbers were far too low. Based on medical reports, unit reports, burial accounts, and other period sources, Heysinger concluded that Lee’s casualty numbers were more than double the traditional figures. According to Heysinger, Lee’s total casualties were 25,330, with 3,500 killed, 16,330 wounded, and 6,000 missing or captured (Antietam and the Maryland and Virginia Campaigns of 1862, New York: The Neale Publishing Company, 1912, pp. 132-141; Heysinger served as a non-commissioned officer in McClellan’s army, fought at Antietam, and later became a noted doctor who received 36 patents).
Another fact that must be considered—and it is a fact McClellan fully understood—is that going into this battle, Lee’s troops were much more experienced than McClellan’s troops. A substantial number of McClellan’s army—including about 20% of his infantry—consisted of new recruits with minimal training, whereas most of Lee’s troops were veterans.
Criticism: The significance of the battle was not Lee's withdrawal, but McClellan's inexplicable failure to pursue. On September 18, the armies remained in their positions without fighting. Lee was highly vulnerable. About one-fourth of his army had been lost in the previous day's fighting, and he had no reserves. After weeks of marching, his men were tired and low on supplies. McClellan, on the other hand, welcomed an additional 12,000 troops on September 18, and he had 24,000 troops who had seen little or no action the day before. He outnumbered Lee by more than two to one. Yet, McClellan refused to pursue Lee.
Response: Some of these criticisms are downright ridiculous, and the troop numbers are based on the dubious assumption that Lee arrived at Antietam with only 43,000 men. The significance of the battle most certainly was Lee’s retreat, not McClellan’s “failure” to immediately pursue Lee. McClellan’s victory over Lee ended Lee’s Maryland campaign, decimated Lee’s officer corps, restored Northern public confidence, enabled Lincoln to issue his preliminary Emancipation Proclamation, and prevented England from recognizing the Confederacy.
Not only did McClellan win at Antietam, but he won the two key battles that led up to Antietam—the Battle of South Mountain and the Battle of Campton’s Gap. McClellan’s critics either ignore or minimize these victories because they resulted from smart decisions and rapid action by McClellan.
The victories at South Mountain and Crampton’s Gap would have ended Lee’s Maryland campaign if Lincoln and Halleck had listened to McClellan when he repeatedly advised them to withdraw the 10,000 troops from Harper’s Ferry and add them to his army. Even before McClellan left Washington, he urged Halleck to withdraw the Harper’s Ferry garrison and add that force to his army while there was still time to do so (Ethan Rafuse, McClellan’s War, pp. 285-286; Harsh, Taken at the Flood, pp. 269-272, 315-316). Lincoln and Halleck rejected McClellan’s request. Their failure to evacuate Harper’s Ferry led to the largest surrender of U.S. troops in the war and convinced Lee not to abandon his Maryland campaign.
After the battles at South Mountain and Crampton’s Gap, Lee concluded that his Maryland campaign was ruined and he began to prepare to return to Virginia. But, he changed his mind when Stonewall Jackson informed him that he had captured Harper’s Ferry, had taken the 10,000 Federal troops there prisoner, and had seized the garrison’s valuable supplies. When Lee heard this, he decided to stay and give battle at Antietam.
Regarding McClellan’s decision not to attack on September 18, he had several good reasons for not attacking. For one thing, he was somewhat low on small-arms ammunition and extremely low on artillery ammunition. A large shipment of artillery shells was supposed to reach McClellan early in the morning on the 18th, but for reasons that remain unknown, there was a six-hour delay between Washington and Baltimore, and the shipment did not reach Hagerstown, over 6 miles from McClellan’s camp, until 1:00 that afternoon (the small-arms ammunition arrived even later). (The train carrying the artillery shells should have made it to the Baltimore station in about 90-100 minutes, which would have enabled it to reach Hagerstown by about 5:30 or 6:00 that morning, but on this occasion the trip took over six hours. To this day, no one knows why this strange delay occurred. The train left Washington before midnight; the train had absolute right of way; and the rail line was clear. Heysinger discusses this strange incident in detail in Antietam and the Maryland and Virginia Campaigns of 1862, pp. 145-149.)
As for the issue pursuit, this is a favorite complaint among amateur critics, and among historians who should know better. In point of act, in several cases Civil War generals did not pursue the defeated army. For example, Grant did not pursue Beauregard’s defeated army as it fled to Corinth after the Battle of Shiloh, even though Grant’s army, recently swelled with reinforcements, heavily outnumbered the Confederate force. Similarly, General George G. Meade wisely decided against attacking Lee’s defeated army immediately after the Battle of Gettysburg. General James Longstreet, one of the South’s best generals, said Lee would have liked nothing better than for Meade to have attacked him soon after Gettysburg because Lee likely would have inflicted the same kind of defeat on Meade that Meade inflicted on Lee in Pickett’s Charge. There were cases in the war when the winning army attacked the defeated army soon after the battle and suffered a nasty repulse.
Furthermore, McClellan did pursue Lee on September 19 as soon as he found out that Lee had retreated from Antietam, but he called off the pursuit after he realized that Lee’s positions across the river were too strong to be carried by the pursuit force and because his army was in no condition to move en masse against Lee’s new positions in Virginia, due to a severe lack of critical supplies. McClellan’s reasons for not attacking Lee with his entire army immediately after Antietam are just as valid and sound as Meade’s reasons for not attacking Lee immediately after Gettysburg. (For a good analysis of the soundness of Meade’s decision not to attack Lee right after Gettysburg, see Tom Huntington, Searching for George Gordon Meade: The Forgotten Victor of Gettysburg, Mechanicsburg, PA: Stackpole Books, 2013, pp. 185-202.)
McClellan might very well have destroyed Lee’s army on September 17 if Lincoln and Halleck had not needlessly kept tens of thousands of troops near Washington instead of letting McClellan have most of them, as he requested. On September 10 and 11, McClellan requested that every available soldier from the Washington area be sent to his army. But Lincoln and Halleck sent him only one corps (Porter’s corps of 13,000 men, which McClellan designated as his reserve force). McClellan’s critics rarely mention this egregious blunder by Lincoln and Halleck, while they are quick to condemn McClellan for not sending in his reserve force during the battle (a move that even the aggressive Porter argued against at the time). General Upton:
While General McClellan has been censured for not engaging the
13,000 men under the command of General Porter, justice requires that we should cast a glance at
the situation around Washington. . . .
On September 11, he . . . recommended . . . "that every available man" be added to his army. The same day he again telegraphed:
“Please send forward all the troops you can spare from Washington, particularly Porter, Heintzelman, Sigel, and all the other old troops. General Banks reports 72,500 troops in and about Washington”. . . .
The commander, as on the Peninsula, sought to place the result of the battle beyond doubt, by asking that every available man be sent forward; yet, at the critical moment when he was censured for not employing his last reserve of 13,000 men, an army stood idle at Washington aggregating present for duty 71,210; present and absent, 107,839. Had 60,000 of these men been sent forward, the raw troops placed in reserve north of the Antietam, the old troops to have joined their veteran comrades in battle, it is fair to infer that little would have been heard of the Confederacy after the Maryland invasion. (The Military Policy of the United States, pp. 383-384)
Criticism: The president was amazed to discover that from September 17 to October 26, despite his and Halleck’s repeated requests, McClellan declined to pursue Lee across the Potomac, claiming he was short of equipment and that his army needed rest. In fact, despite repeated urging Lincoln and Halleck, McClellan did not move toward Virginia until five weeks after the battle. McClellan was not short of supplies and his army was no more exhausted than was Lee’s army.
Response: This is a mix of myth and distortion. For starters, the fact that McClellan’s army was badly lacking in critical supplies is abundantly documented in the relevant primary sources and has been discussed in numerous analyses of the aftermath of Antietam (see, for example, Rafuse, McClellan’s War, pp. 350-359; George Ticknor Curtis, McClellan’s Last Service to the Republic, New York: D. Appleton and Company, 1886, pp. 61-71; see also below).
General Meade, one of McClellan’s subordinate commanders, went so far as to accuse the War Department of deliberately withholding supplies from the army. Quite of a few of McClellan’s subordinate officers believed that Stanton delayed the arrival of supplies so he could then blame McClellan for “excessive delay.” Stanton never did provide a credible innocent explanation for the long delay in getting supplies to McClellan’s army.
Stanton claimed that the tons of supplies intended for McClellan’s army at Harper’s Ferry had been mistakenly, accidentally sent to the troops garrisoned around the capital. But Stanton, along with everybody else in the War Department, knew that McClellan’s army was at Harper’s Ferry, over 60 miles away. For nearly three weeks, McClellan complained in his dispatches to the War Department that he was not receiving the supplies he had requested, yet Stanton and Halleck, along with Republican newspapers, kept insisting that the supplies had been sent and that McClellan had all the supplies he needed to pursue Lee in Virginia.
When confronted with an eyewitness report from Colonel Thomas Scott that McClellan had not received the supplies, Stanton and/or Halleck “suggested” that the supplies had been sent to the garrison units around the capital, since those units were technically part of the Army of the Potomac. No one ever explained how the tons of supplies requested by McClellan for his army at Harper’s Ferry could have been “mistakenly” sent to the capital’s garrison units when everyone in Washington knew that McClellan’s army was over 60 miles away. In fact, upon further investigation, train loads of the supplies that McClellan had requested “were found on the tracks at Washington, where some of the cars had been for weeks” (William H. Powell, The Fifth Army Corps--Army of the Potomac: A Record of Operations During the Civil War in the United States of America, 1861-1865, New York: G. P. Putnam’s Sons, 1893, p. 311, emphasis added).
Also, Lincoln had no reason to be amazed that McClellan had to resupply his army before moving against Lee in Virginia, because Lincoln soon became aware of the fact that the supplies that Stanton had claimed had been sent to McClellan had not been delivered to him, and that McClellan’s army was in fact suffering from a severe shortage of basic supplies. As soon as those supplies were finally delivered, McClellan was only too happy to begin his move against Lee in Virginia.
Part of the problem was that Lincoln was virtually illiterate when it came to military matters. For all his good qualities, Lincoln did not understand even the basics of military operations. On many occasions, he imposed faulty strategies and unsound deployments on his commanders, especially on McClellan. Lincoln also frequently pestered commanders for updates and offered baseless and annoying comments on ongoing military operations. Lincoln should have understood that McClellan’s army would be in great need of resupply after fighting several intense battles during the preceding two weeks—including the single bloodiest day of combat in the entire war—and given the fact that McClellan’s “army” had been hastily thrown together after Pope’s debacle at Second Bull Run just two weeks before Antietam.
Regarding the claim that McClellan should not have taken five weeks to rest and resupply his army after Antietam before going after Lee in Virginia, we might want to consider what Colonel Robert Gould Shaw had to say on the matter. Shaw was in McClellan's army at the time, and students of the Civil War know that Shaw was no shrinking violet when it came to combat. In a letter to his mother, dated September 25, 1862, barely a week after the battle, he made it known that he strongly agreed with McClellan's decision to rest and resupply the army after Antietam and not to move immediately to pursue Lee--he also provided some insight into the supply shortage, the one that the Radicals claimed did not exist:
We are regularly encamped up here now, and hope to stay some time, for the army certainly needs rest; and Heaven preserve us from a winter campaign! If any newspaper talks of "On to Richmond" after the middle of November, let the editors come down and try it themselves; from what we experienced the first six weeks of this campaign, I am certain only about half the army would live through it; the wet and cold together are too much for men who can seldom change shoes or clothing, and most of whom are without Indian rubber blankets. A wet overcoat, and woolen blanket in the same condition, are very small protection. We have four to six wagons per regiment now, so that no extra clothing can be carried. (Russell Duncan, editor, Blue-Eyed Child of Fortune: The Civil War Letters of Colonel Robert Gould Shaw, University of Georgia Press, 1992, p. 244)
