It was first intended to keep this corps in reserve on the east side of the Antietam, to operate on either flank or on the center, as circumstances might require. But, on nearing Keadysville, the strong opposition on the right, developed by the attacks of Hooker and Sumner, rendered it necessary to send this corps at once to the assistance of the right wing. On nearing the field, hearing that one of our batteries ("A," 4th U. S. Artillery), commanded by Lieutenant Thomas, who occupied the same position as Lieutenant Woodruff's battery in the morning, was hotly engaged, without supports, General Smith sent two regiments to its relief from General Hancock's brigade. On inspecting the ground, General Smith ordered the other regiment of Hancock's brigade, with Frank's and Cowen's batteries, 1st New York Artillery, to the threatened position ; Lieutenant Thomas and Captain Cothran, commanding batteries, bravely held their positions against the advancing enemy, handling their batteries with skill.

Towards the middle of the afternoon, proceeding to the right, I found that Sumner's, Hooker's, and Mansfield's corps had met with serious losses. Several general officers had been carried from the field severely wounded, and the aspect of affairs was anything but promising. At the risk of greatly exposing our center, I ordered two brigades from Porter's corps, the only available troops, to reenforce the right. Six battalions of Sykes's regulars had been thrown across the Antietam bridge on the main road, to attack and drive back the enemy's sharpshooters, who were annoying Pleasonton's horse batteries in advance of the bridge. Warren's brigade of Porter's corps was detached to hold a position on Burnside's right and rear, so that Porter was left at one time with only a portion of Sykes's division, and one small brigade of Morell's division (but little over three thousand men) to hold his important position.

General Sumner expressed the most decided opinion against another attempt during that day to assault the enemy's position in front, as portions of our troops were so much scattered and demoralized. In view of these circumstances, after making changes in the positions of some of the troops, I directed the different commanders to hold their positions, and, being satisfied that this could be done without the assistance of the two brigades from the center, I countermanded the order which was in course of execution.

On the morning of the 17th the troops of General Burnside held the left of the line opposite bridge No. 3. The attack on the right was to have been supported by an attack on the left. Preparatory to this attack, on the evening of the 16th, General Burn-side's corps was moved forward and to the left, and took up a position nearer the bridge.

I visited General Burnside's position on the 16th, and after pointing out to him the proper dispositions to be made of his troops during the day and night, informed him that he would probably be required to attack the enemy's right on the following morning, and directed him to make careful reconnoissances.

Early on the morning of the 17th, I ordered General Burnside to form his troops, and hold them in readiness to assault the bridge in his front, and to await further orders.

At eight o'clock an order was sent to him by Lieutenant Wilson, Topographical Engineers to carry the bridge, then to gain possession of the heights beyond, and to advance along their crest upon Sharpsburg and its rear.

After some time had elapsed, not hearing from him, I despatched an aide to ascertain what had been done. The aide returned with the information that but little progress had been made. I then sent him back with an order to General Burnside, to assault the bridge at once, and carry it at all hazards. The aide returned to me a second time, with the report that the bridge was still in the possession of the enemy. Whereupon I directed Colonel Sackett, Inspector General, to deliver to General Burnside my positive order to push forward his troops without a moment's delay, and, if necessary, to carry the bridge at the point of the bayonet, and I ordered Colonel Sackett to remain with General Burnside and see that the order was executed promptly.

After these three hours' delay, the bridge was carried at 1 o'clock by a brilliant charge of the 51st New York and 51st Pennsylvania Volunteers. Other troops were then thrown over and the opposite bank occupied, the enemy retreating to the heights beyond.

A halt was then made by General Burnside's advance until 3 p. m., upon hearing which I directed one of my aides Colonel Key to inform General Burnside that I desired him to push forward his troops with the utmost vigor and carry the enemy's position on the heights ; that the movement was vital to our success ; that this was a time when we must not stop for loss of life if a great object could be thereby accomplished. That if, in his judgment, his attack would fail, to inform me so at once, that his troops might be withdrawn and used elsewhere on the field. He replied that he would soon advance, and would go up the hill as far as a battery of the enemy on the left would permit. Upon this report I again immediately sent Colonel Key to General Burnside, with orders to advance at once, if possible, to flank the battery or storm it and carry the heights, repeating that if he considered the movement impracticable to inform me so, that his troops might be recalled. The advance was then gallantly resumed, the enemy driven from their guns, the heights handsomely carried, and a portion of the troops even reached the outskirts of Sharpsburg. By this time it was nearly dark, and strong re6nforcemelits just then reaching the enemy from Harper's Ferry, attacked General Burnside's troops on their left flank, and forced them to retire to a lower line of hills nearer the bridge.

If this important movement had been consummated two hours earlier, a position would have been secured upon the heights from which our batteries might have enfiladed the greater part of the enemy's line, and turned their right and rear. Our victory might have been much more decisive.

It was now nearly dark. General Sturgis was ordered forward to support the left. Notwithstanding the hard work in the early part of the day, his division moved forward with spirit. With its assistance, the enemy were checked and held at bay.

The command was ordered to fall back by General Cox, who commanded, on the field, the troops engaged in this attack beyond the Antietam. The artillery had been well served during the day. Night closed the long and desperately contested battle of the 1 7th. Nearly 209,000 men, and 500 pieces of artillery, were for fourteen hours engaged in this memorable battle. We had attacked the enemy in a position selected by the experienced engineer then in person directing their operations. We had driven them from their line on one flank, and secured a footing within it on the other. The Army of the Potomac, notwithstanding the moral effect incident to previous reverses, had achieved a victory over an adversary invested with the prestige of recent success. Our soldiers slept that night, conquerors, on a field won by their valor, and covered with the dead and wounded of the enemy.