McClernand's division was swept from the ground which it had occupied. The desired road for retreat was open to the besieged. Buckner was in the position assigned to him, and halting, awaited his artillery and reserves from the intrenchments. General Pillow, who now found himself within the intrenchments at the salient, held by Colonel Heiman, directed the artillery to remain, and sent reiterated orders to Buckner to return and resume his position within the works. He was in the act of returning when he met General Floyd, who seemed surprised at the movement. After some conversation, in which both agreed that the original plan should be carried out, Floyd directed Buckner to remain till he could see Pillow. After consulting with Pillow, Floyd sent orders to Buckner to retire within the lines, and to repair as rapidly as possible to his former position on the extreme right, which was in danger of attack. By order of General B.R. Johnson, Colonel Drake's brigade and the Twentieth Mississippi remained on the field.

General Grant, at his interview on the flag-ship, was advised of the serious injury to the fleet, and informed that Commodore Foote, leaving his two ironclads least injured to protect the transports at the landing, would proceed to Cairo with the other two, repair them, hasten the completion of the Benton and mortar-boats, and return to the prosecution of the siege. General Grant, upon this, made up his mind to intrench, and with reinforcements complete the investment of the enemy's works. Reaching the lines about one o'clock on his return, he learned the state of affairs, ordered General C.F. Smith to prepare to storm the works in his front, repaired to the right, inspected the condition of the troops, and gave orders to be ready to attack when General Smith should make his assault.

The Fifty-second Indiana had been detached from Colonel Cook's brigade to watch a gap in the intrenchments, near the extreme right of the besieged line. At two o'clock General Smith ordered the assault by Lauman's brigade; the Fifty-second Indiana was temporarily attached to the brigade. The assaulting force was formed in column of battalions of five companies each. The Second Iowa was in advance, with General Smith in its centre, and followed in order by the Fifty-second Indiana, Twenty-fifth Indiana, Seventh Iowa, and Fourteenth Iowa. Birge's sharpshooters, deployed on each flank, opened a skirmishing fire. The column advanced silently, without firing, crushed down the abattis, covered the hill-side with battalions, heedless of the fire from the garrison, pressed on to the works, leaped over, formed in line, and drove the defending regiment to further shelter.

Just at this time General Buckner was gaining this, the extreme right of the line of intrenchments, with Hanson's regiment, which had left it in the morning for the sortie. Hanson pushed his men forward, but the works were occupied. The Thirtieth Tennessee, which had been holding that portion of the works during the day, fell back to another ridge or spur, between the captured work and the main fort. Lauman's brigade pushed on to assault that position. Hanson's regiment, the Third, Eighteenth, and Forty-first Tennessee and Fourteenth Mississippi, came to the aid of the Thirtieth; portions of Porter's and Graves' batteries were brought up. The Forty-ninth and Fiftieth Tennessee, the garrison of the fort, hastened out in support. General Smith sent for Cook's brigade and artillery. Lieutenant-Colonel McPherson sent up two ten-pound Parrott guns. Buckner held the inner ridge, to which his men had retired, and intrenched it in the night. Smith held the works he had gained, an elevation as high as any within the line. His battery established there, enfiladed part of the line still held, and took in reverse nearly the whole of the intrenchments. In the charge, the column, including Birge's sharpshooters, but excluding the Fifty-second Indiana, lost 61 killed and 321 wounded; of these, the Second Iowa lost 41 killed and 157 wounded. General Smith, though sixty years old, spent the night without shelter, on the captured ridge.

General Grant, having set in motion C.F. Smith's attack, rode to the right and ordered the troops there to take the offensive and regain the ground that had been lost. General Lewis Wallace moved with a brigade commanded by Colonel Morgan L. Smith, and made of the Eighth Missouri and Eleventh Indiana, in advance. These two regiments belonged to Smith's division, and marched from Fort Henry to Donelson with Wallace. Colonel M.L. Smith, in his report, calls this command the Fifth Brigade, Third Division. The regimental commanders in their reports style it, Fifth Brigade, General C.F. Smith's division. Following was Cruft's brigade. General Wallace says, in his report: "As a support, two Ohio regiments, under Colonel Ross, were moved up and well advanced on the left flank of the assailing force, but held in reserve." Colonel Ross, of the Seventeenth Illinois, arriving at the front that morning and reporting for duty, was at once assigned to the command of the brigade composed of the Seventeenth and Forty-ninth Illinois, and, as ordered by General McClernand, moved with General Wallace in support and reserve, till recalled about dark by McClernand. An Ohio regiment, the Twentieth, Colonel Whittlesey, did go out in support and reserve, but it was not under Colonel Ross, and it remained close to the enemy's works all night.

The column approached the ridge held by Drake's brigade and the Twentieth Mississippi. M.L. Smith's brigade came in front, where the slope was bare; Cruft had to push up through bushes. General Wallace speaks with admiration of the advance by Smith. He advanced his line and ordered it to lie down, and to continue firing while lying down. As soon as the fire of the enemy on the summit slackened, the regiments rose, dashed up the hill, and lay down again before the fire from the hill-top could be made effective. In a short time, with rapid bounds, the summit was gained. Cruft's brigade pushed up through the bushes. Drake fell back within the intrenchments. Wallace stationed his picket-line close to the enemy's works. The retiring Confederate force took with them six captured pieces of artillery, several thousand small arms, and between two and three hundred prisoners; but returned to their trenches weary, disappointed, disheartened.

In the night General Floyd and General Buckner met with General Pillow and his staff, at General Pillow's headquarters, to consider the situation. After some recrimination between Pillow and Buckner whether the intention and plan had been to commence the retreat directly from the battlefield, or first to cut a way out and then return to the works, equip for a march and retreat by night, it was agreed to evacuate that night and march out by the ground which had been gained. Pillow ordered the chief quartermaster and the chief commissary to burn the stores at half-past five in the morning. Precaution was taken, however, before actually preparing for the movement, to send out scouts to see if the way were still clear. The scouts returned with report that the National forces had reoccupied the ground. This being doubted, other scouts were sent out, who brought the same report in more positive terms. Pillow proposed to cut a way out. Buckner said that was now impossible, and Floyd acquiesced. Pillow at last assented to this, but proposed to hold the fort at least one day longer and take the chances of getting out. Buckner said that was impossible; a lodgement had been made in the key of his position; assault would certainly follow as soon as it was light, and he could not withstand it. It was remarked that no alternative was left but to surrender. General Floyd said he would never surrender—he would die first. Pillow said substantially the same. Buckner said, if he were in command, he would surrender and share the fate of the garrison. Floyd inquired of Buckner, "If the command should devolve on you, would you permit me to take out my brigade?" To which Buckner replied, "Yes, if you leave before the terms of capitulation are agreed on." Forrest asked, "Gentlemen, have I leave to cut my way out?" Pillow answered, "Yes, sir, cut your way out," and asked, "Is there anything wrong in my leaving?" Floyd replied, "Every person must judge for himself of that?" Whereupon General Pillow said, "Then I shall leave this place." General Floyd turned to General Pillow and told him, "General Pillow, I turn the command over, sir." General Pillow said, "And I pass it." General Buckner said, "And I assume it," and countermanded the order for the destruction of the commissary and quartermaster stores, and ordered white flags to be prepared and a bugler to report to him.

At eleven o'clock that night Floyd telegraphed to General A.S. Johnston a glorious victory. Four hours later, at the close of the council or conference, he telegraphed: "We are completely invested by an army many times our numbers. I regret to say the unanimous opinion of the officers seems to be that we cannot maintain ourselves against these forces."

Colonel Forrest reported that upon examination he found that deep mud and water made an escape by land, between the investing force and the river, impracticable for infantry. Forrest marched out with all the cavalry but Gantt's Tennessee battalion and two companies of Helm's Kentucky cavalry, taking with him the horses of Porter's battery and about two hundred men of various commands. There was not a steamboat at the landing; General Floyd had sent all up the river with wounded and prisoners. Not a skiff or yawl could be found. A little flatboat or scow was got by some means from the other side of the river, and on this General Pillow crossed the river with his staff and Colonel Gilmer. Two steamboats returned at daybreak, one of them bringing "about four hundred raw troops." The four hundred raw troops were dumped on shore, and Floyd took possession of the boats. Floyd's brigade, consisting of four Virginia regiments and the Twentieth Mississippi, had been divided during the siege. The four Virginia regiments were organized into two brigades, and the Twentieth Mississippi attached to another command. Two Virginia regiments were ferried across the river, and the Twentieth Mississippi, understanding that they were to be taken on board with Floyd, stood on guard and kept off the growing crowd of clamorous soldiers while the other two Virginia regiments embarked. The rope was cut and Floyd steamed up the river, leaving the Twentieth Mississippi and his aide-de-camp, Lieutenant Breckenridge Drake, behind. It was said afterward that word was received from General Buckner that the boat must leave at once, or it would not be allowed to leave.

Soon after daybreak, Sunday the 16th, the men of Lauman's brigade heard the notes of a bugle advancing from the fort. It announced an officer, who bore to General Grant a letter from General Buckner, proposing the appointment of commissioners to agree upon terms of capitulation, and also proposing an armistice until noon. General Grant replied, acknowledging the receipt of the letter, and adding: "No terms except an unconditional and immediate surrender can be accepted. I propose to move immediately upon your works." Buckner replied: "The distribution of the forces under my command, incident to an unexpected change of commanders, and the overwhelming force under your command, compel me, notwithstanding the brilliant success of the Confederate arms yesterday, to accept the ungenerous and unchivalrous terms which you propose." White flags were displayed along the works; the National troops marched in, and General Grant at once made the following order: "All prisoners taken at the surrender of Fort Donelson will be collected as rapidly as practicable near the village of Dover, under their respective company and regimental commanders, or in such manner as may be deemed best by Brigadier-General S.B. Buckner, and will receive two days' rations preparatory to embarking for Cairo. Prisoners are to be allowed their clothing, blankets, and such private property as may be carried about the person, and commissioned officers will be allowed their side-arms."