The battle was a fierce one from the moment Willcox's men showed themselves on the open ground. Christ's brigade, taking advantage of all the cover the trees and inequalities of surface gave them, pushed on along the depression in which the road ran, a section of artillery keeping pace with them in the road. The direction of movement brought all the brigades of the first line in echelon, but Welsh soon fought his way up beside Christ, and they together drove the enemy successively from the fields and farm-yards till they reached the edge of the village. Upon the elevation on the right of the road was an orchard in which the shattered and diminished force of Jones made a final stand, but Willcox concentrated his artillery fire upon it, and his infantry was able to push forward and occupy it. They now partly occupied the town of Sharpsburg, and held the high ground commanding it on the southeast, where the National Cemetery now is. [Footnote: Official Records, vol. xix. pt. i. p. 431.] The struggle had been long and bloody. It was half-past four in the afternoon, and ammunition had again run low, for the wagons had not been able to accompany the movement. Willcox paused for his men to take breath again and to fetch up some cartridges; but meanwhile affairs were taking a serious turn on the left.
As Rodman's division went forward, he found the enemy before him seemingly detached from Willcox's opponents, and occupying ridges on his left front, so that he was not able to keep his own connection with Willcox in the swinging movement to the right. Still, he made good progress in the face of stubborn resistance, though finding the enemy constantly developing more to his left, and the interval between him and Willcox widening. The view of the field to the south was now obstructed by fields of tall Indian corn, and under this cover Confederate troops approached the flank in line of battle. Scammon's officers in the reserve saw them as soon as Rodman's brigades echeloned, as these were toward the front and right. This hostile force proved to be A. P. Hill's division of six brigades, the last of Jackson's force to leave Harper's Ferry, and which had reached Sharpsburg since noon. Those first seen by Scammon's men were dressed in the National blue uniforms which they had captured at Harper's Ferry, and it was assumed that they were part of our own forces till they began to fire. [Footnote: Official Records, vol. xix. pt. i. p. 468.] Scammon quickly changed front to the left, drove back the enemy before him, and occupied a line of stone fences, which he held until he was afterward withdrawn from it. [Footnote: Id., p. 466.] Harland's brigade was partly moving in the corn-fields. One of his regiments was new, having been organized only three weeks, and the brigade had somewhat lost its order and connection when the sudden attack came. Rodman directed Colonel Harland to lead the right of the brigade, while he himself attempted to bring the left into position. In performing this duty he fell, mortally wounded. Harland's horse was shot under him, and the brigade broke in confusion after a brief effort of its right wing to hold on. Fairchild also now received the fire on his left, and was forced to fall back and change front. [Footnote: Id., pp. 451, 453.]
Being at the centre when this break occurred on the left, I saw that it would be impossible to continue the movement to the right, and sent instant orders to Willcox and Crook to retire the left of their line, and to Sturgis to come forward into the gap made in Rodman's. The troops on the right swung back in perfect order; Scammon's brigade hung on at its stone wall at the extreme left with unflinching tenacity till Sturgis had formed on the curving hill in rear of them, and Rodman's had found refuge behind. Willcox's left then united with Sturgis, and Scammon was withdrawn to a new position on the left flank of the whole line. That these manoeuvres on the field were really performed in good order is demonstrated by the fact that although the break in Rodman's line was a bad one, the enemy was not able to capture many prisoners, the whole number of missing, out of the 2349 casualties which the Ninth Corps suffered in the battle, being 115, which includes wounded men unable to leave the field. [Footnote: Official Records, vol. xix. pt. i. pp. 200, 427.]
The enemy were not lacking in bold efforts to take advantage of the check we had received, but were repulsed with severe punishment, and as the day declined were content to entrench themselves along the line of the road leading from Sharpsburg to the Potomac at the mouth of the Antietam, half a mile in our front. The men of the Ninth Corps lay that night upon their arms, the line being one which rested with both flanks near the Antietam and curved outward upon the rolling hill-tops which covered the bridge and commanded the plateau between us and the enemy. With my staff, I lay upon the ground behind the troops, holding our horses by the bridles as we rested, for our orderlies were so exhausted that we could not deny them the same chance for a little broken slumber.
The Ninth Corps occupied its position on the heights west of the Antietam without further molestation, except an irritating picket firing, till the Confederate army retreated on the 19th of September. But the position was one in which no shelter from the weather could be had, nor could any cooking be done; and the troops were short of rations. My division wagon-train, which I had brought from the West, here stood us in good stead, for the corps as a whole was very short of transportation. The energy of Captain Fitch, my quartermaster, forced the train back and forth between us and the nearest depot of supplies, and for several days the whole corps had the benefit of the provisions thus brought forward. Late in the afternoon of Thursday the 18th, Morell's division of Porter's corps was ordered to report to Burnside to relieve the picket line and some of the regiments in the most exposed position. One brigade was sent over the Antietam for this purpose, and a few of the Ninth Corps regiments were enabled to withdraw far enough to cook some rations, of which they had been in need for twenty-four hours. [Footnote: General Porter in his report says Morell took the place of the whole Ninth Corps. In this he is entirely mistaken, as the reports from Morell's division, as well as those of the Ninth Corps, show.] Harland's brigade of Rodman's division had been taken to the east side of the stream to be reorganized, on the evening of Wednesday the 17th. The sounds heard within the enemy's lines by our pickets gave an inkling of their retrograde movement in the night of Thursday, and at break of day on Friday morning the retreat of Lee's whole army was discovered by advancing the picket line. Reconnoissances sent to the front discovered that the whole Confederate army had crossed the Potomac.
The conduct of the battle on the left has given rise to several criticisms, among which the most prominent has been that Porter's corps, which lay in reserve, was not put in at the same time with the Ninth Corps. It has been said that some of them were engaged or in support of the cavalry and artillery at the centre. This does not appear to have been so to any important extent, for no active fighting was going on elsewhere after Franklin's corps relieved Sumner's about noon. McClellan's reports do not urge this. He answered the criticism by saying that he did not think it prudent to divest the centre of all reserve troops. No doubt a single strong division, marching beyond the left flank of the Ninth Corps, would have so occupied A. P. Hill's division that our movement into Sharpsburg could not have been checked, and, assisted by the advance of Sumner and Franklin on the right, would apparently have made certain the complete rout of Lee. As troops are put in reserve, not to diminish the army, but to be used in a pinch, I am convinced that McClellan's refusal to use them on the left was the result of his rooted belief, through all the day after Sedgwick's defeat, that Lee was overwhelmingly superior in force, and was preparing to return a crushing blow upon our right flank. He was keeping something in hand to fill a gap or cover a retreat, if that wing should be driven back. Except in this way, also, I am at a loss to account for the inaction of the right during the whole of our engagement on the left. Looking at our part of the battle as only a strong diversion to prevent or delay Lee's following up his success against Hooker and the rest, it is intelligible. I certainly so understood it at the time, as my report witnesses, and McClellan's original report sustains this view. [Footnote: Official Records, vol. xix. pt. i. pp. 31, 426.] If he had been impatient to have our attack delivered earlier, he had reason for double impatience that Franklin's fresh troops should assail Lee's left simultaneously with our assault of his other wing, unless he regarded action there as hopeless, and looked upon our movement as a sort of forlorn hope to keep Lee from following up his advantages.
But even these are not all the troublesome questions requiring an answer. It will be remembered that Franklin's corps, after forcing Crampton's Gap, had remained in Pleasant Valley between Rohrersville and Boonsboro until Tuesday night (16th September). McClellan then ordered Couch's division to be sent to occupy Maryland Heights and observe the enemy in Harper's Ferry, whilst Franklin with Smith's and Slocum's divisions should march to the battle-field at daybreak of Wednesday. Why could not Couch be called up and come on our left as well as A. P. Hill's division, which was the last of the Confederate troops to leave the ferry, there being nothing to observe after it was gone? Couch's division, coming with equal pace with Hill's on the other side of the river would have answered our needs as well as one from Porter's corps. Hill came, but Couch did not. Yet even then, a regiment of horse, watching that flank and scouring the country as we swung forward, would have developed Hill's presence and enabled the commanding general either to stop our movement or to take the available means to support it. The cavalry was put to no such use. It occupied the centre of the whole line, only its artillery being engaged during the day. It would have been invaluable to Hooker in the morning, as it would have been to us in the afternoon.
McClellan had marched from Frederick City with the information that Lee's army was divided, Jackson being detached with a large force to take Harper's Ferry. He had put Lee's strength at 120,000 men. Assuming that there was still danger that Jackson might come upon our left with his large force, and that Lee had proven strong enough without Jackson to repulse three corps on our right and right centre, McClellan might have regarded his own army as divided also for the purpose of meeting both opponents, and his cavalry would have been upon the flank of the part with which he was attacking Lee; Porter would have been in position to help either part in an extremity or to cover a retreat; and Burnside would have been the only subordinate available to check Lee's apparent success. Will any other hypothesis intelligibly account for McClellan's dispositions and orders? The error in the above assumption would be that McClellan estimated Lee's troops at nearly double their actual numbers, and that what was taken for proof of Lee's superiority in force on the field was a series of partial reverses which resulted directly from the piecemeal and disjointed way in which McClellan's morning attacks had been made.
The same explanation is the most satisfactory one that I can give for the inaction of Thursday, the 18th of September. Could McClellan have known the desperate condition of most of Lee's brigades, he would also have known that his own were in much better case, badly as they had suffered. I do not doubt that most of his subordinates discouraged the resumption of the attack, for the belief in Lee's great preponderance in numbers had been chronic in the army during the whole year. That belief was based upon the inconceivably mistaken reports of the secret-service organization, accepted at headquarters, given to the War Department at Washington as a reason for incessant demands of reinforcements, and permeating downward through the whole organization till the error was accepted as truth by officers and men, and became a factor in their morale which can hardly be overestimated. The result was that Lee retreated unmolested on the night of the 18th of September, and that what might have been a real and decisive success was a drawn battle in which our chief claim to victory was the possession of the field.
The numbers engaged and the losses on each side have been the subject of unending dispute. If we take the returns of Lee at the beginning of his campaign against Pope, and deduct his acknowledged losses, he crossed the Potomac with over 72,000 men. [Footnote: See my review of Henderson's Stonewall Jackson, "The Nation," Nov. 24, 1898, p.396.] If we take his returns of September 22, and add the acknowledged losses of the month, he had over 57,000. [Footnote: See my review of Allan's Army of Northern Virginia, "The Nation," Feb. 2, 1893, p.86. Also reply to General Fitzhugh Lee, Id., Dec. 20, 1894, p.462; Confederate Statistics, Id., Jan. 24, 1895, p.71; Review of Ropes's Story of the Civil War, Id., March 9, 1899, p.185.] McClellan's 87,000 present for duty is accepted by all, though various causes considerably reduced the number he brought into action. The best collation of reports of casualties at Antietam gives 12,410 as those on the National side, and 11,172 on the Confederate. [Footnote: Century War Book, vol. ii. p.603.] Longstreet, comparing the fighting in the fiercest battles of the war, says "on no single day in any one of them was there such carnage as in this fierce struggle." [Footnote: From Manassas to Appomattox, p.239.]