Grant had about 27,000 men with naval support; the Confederate garrison was roughly 15,000.

Union losses were about 2,250 while the Confederates had about that many fall, and roughly 12,000 surrender.

After capturing Fort Henry on February 6, 1862, Grant advanced cross-country to invest Fort Donelson. The original garrison of the two forts was about 2,500 men, and Albert Johnston had dispatched about 12,000 reinforcements from Bowling Green, KY, under John Floyd to bolster the defense. A few men also arrived from Columbus, the western end of the Confederate defensive line. Grant had wanted to move fast, to prevent reinforcements arriving at all, but wretched weather (rain before and during his operations ruined the roads) delayed him and the Confederate troops arrived safely.

Fort Donelson was a much stronger work than Fort Henry, larger, with a stronger garrison, about 100 feet above the river (so it had plunging fire on ships), and on a ridge which narrowed routes for infantry attack. The Confederates had a strong line on the next ridge outwards from the fort, with each of the Generals commanding a sector while Floyd (the senior) also had overall command. Grant deployed two divisions in line, with a third arriving. On the 12th, despite orders not to, McClernand had one of his brigades probe the Confederate defenses. They charged two or three times and found the defenses strong and well manned: Union losses were heavy. (Grant had intended simply to surround the fort and have the Navy batter it into submission.)

On the 13th the third Union division arrived (Lew Wallace’s) and Grant had his cordon of roughly 25,000 men. The next day Foote opened his naval attack. He had four ironclads and two wooden gunboats, and he led with the ironclads. St Louis (flagship) and Louisville had their steering gear shot away, the other two ironclads had holes punched through their thinner deck armor. The wooden ships didn’t risk themselves much. The Confederates didn’t lose a gun or a man killed.

Grant was in a bind. It suddenly looked like he faced a long siege, since the navy couldn’t win it for him. Worse, he had a green army and he didn’t think he could storm the Fort. Finally, the weather was dreadful, wet formerly and not frosty as well, and the army didn’t have tents. Meanwhile, the Confederates could supply themselves along the river, protected by the Fort. Confederate stupidity bailed Grant out.

The Confederates didn’t think about supplying themselves by water; it was unconventional, and they were cut off by land. They also thought Grant was stronger than he really was, and being continually reinforced. They worried that Foote would turn up with another fleet. In a council of war on the night of February 14, they decided to try and break out.

The plan was to reinforce the left (Pillow) with Buckner’s men from the right. Pillow would lead the attack and clear the road to Charlotte and Nashville. Buckner’s men would keep the road open while the rest of the garrison was evacuated, and everybody would join the main army in central Tennessee. It almost happened. Pillow, with Buckner joining the attack, broke the Union line in late morning. They captured 300 prisoners, about 5,000 rifles, and an artillery battery. Indecision then lost the victory. Pillow was cautious, Buckner bold, and Floyd foolish. After hemming and hawing Floyd ordered his (victorious) men to return to the trenches. Meanwhile Grant returned to the field. He’d been conferring with Foote (wounded, so the conference had to be on the gunboat) and returned in time to rescue the battle.

He ordered his reserve into action, attacking the Fort rather than the victorious Confederate left. The deploying attack was what drew the Confederates back to their trenches, but Buckner’s men didn’t arrive in time. They held the Union to only limited gains, but the Confederate’s main defensive line was broken. They had broken the Union line, but snatched defeat from the jaws of victory. Grant also rallied his right, and reoccupied most of the ground lost in the morning, so the day closed with a near-total Union advantage.

One opportunity remained for the Southerners: McClernand hadn’t blocked the river road; a part, perhaps a substantial part, of the Confederate forces could escape. Floyd lacked the strength of will to risk his men, and held another council of war. The decision was to surrender. But Floyd decided that wasn’t good enough for him. He reckoned his own life was at risk if he was taken prisoner (as U.S. Secretary of War he’d made some decisions that helped the seceding states, and he was under indictment) and hopped on the last steamer to Nashville. (He did take about 2,000 Virginia infantry with him.) Gideon Pillow then declared he was too valuable to lose, and Buckner was left to make the actual surrender, although he’d always argued for more fighting. Another man refused to surrender, and Nathan Forrest broke out along the river road with his cavalry regiment and a few infantry.

On February 16, 1862, the 12,000-man garrison surrendered. Buckner had enquired about terms and Grant uncompromisingly replied “No terms except an unconditional and immediate surrender can be accepted.” Buckner fumed that it was “ungenerous and unchivalrous” but it was warlike. With a demoralized command he had no choice.

This was a major victory for Grant and a catastrophe for the South. It ensured that Kentucky would stay in the Union and opened up central Tennessee to a Northern advance along the Tennessee and Cumberland rivers. Grant received a promotion to major general for his victory and attained stature in the Western Theater, earning the nom de guerre “Unconditional Surrender.”

Content provided by:
eHistory Staff

Selected sources:
American Battlefield Protection Program, Heritage Preservation Services, National Park Service.