Fort Donelson was a significant Confederate fort defending the Cumberland River in northern Tennessee (American Civil War). It was a key part of the Confederate defensive line at the start of 1862, but was vulnerable to attack by Union forces based at Cairo, the junction of the Ohio and Mississippi Rivers. The commander of these forces was U. S. Grant, as yet unknown, but about to make his reputation.
The security of the Confederate line depended on each strong point being retained. However, Fort Henry on the Tennessee River was a weak point in the line, and on 6 February 1862 it fell to a force led by U. S. Grant (although his infantry did not arrive in time to take part in the battle). Most of the 2,500 strong garrison of Fort Henry reached Fort Donelson, raising the garrison there to 5,000. Donelson was a much stronger position than Fort Henry, but even the enhanced garrison would be outnumbered 3 to 1 by Grant’s 15,000 Union soldiers.
The Confederate commander in the west, General A. S. Johnston, was faced with two alternatives. He could either abandon Fort Donelson and the defensive line in Tennessee, using the troops thus released to form a powerful field army which could then launch a counterattack, or he could move his entire army to Fort Donelson, smash Grant’s army and then turn on a second Union army under General Buell that was threatening from the north east.
At first Johnston decided to pull back and prepare a counterattack, but eventually he decided to combine both plans. He sent 12,000 men to reinforce Fort Donelson, bringing the garrison there up to 17,000 men, temporarily outnumbering Grant’s 15,000. However, Grant was expected 10,000 reinforcements. Johnston’s action weakened his field army without giving the garrison of Fort Donelson a realistic chance of defeated Grant.
Grant’s men arrived at Fort Donelson on 12 February. An attack the following day was repulsed, before on 14 February Grant’s reinforcements (and Foote’s ironclad gunboats) arrived. This time the gunboats were not able to stand up to rather more effective Confederate gunfire. Grant prepared to settle down for a conventional siege.
He now made what was to become a characteristic error. Confident that he was in command of the situation, Grant did not expect a Confederate attack. However, on the morning of 15 February that is exactly what happened. The besieged Confederate defenders of the fort had decided that their best hope of escape was to break through the Union lines and escape. When the attack came, Grant was five miles away, meeting Foote. McClernand’s division took the brunt of the Confederate attack, and was close to breaking when the Confederate second in command, General Pillow, became convinced that his men were too exhausted to risk the cross-country march. He was able to persuade the commander of the garrison, General Floyd, to order his men back into their trenches.
It was at this point that Grant arrived at the battlefield. Despite the Confederate lapse, his siege lines were broken, and it was surely only a matter of time before the Confederates recovered their nerve and escaped. Grant did not give them the time to recover. Instead he managed to organise a strong enough force to launch a counterattack, and with some aid from the gunboats recaptured the ground lost while he had been absent.
Within Fort Donelson it was now obvious that the only option was surrender. However, neither Floyd or Pillow remained to enter captivity. Both had been politically active before the war, and could not expect a comfortable time in Northern captivity. Both men escaped, leaving General Buckner, the third in command, to actually surrender the fort.
The negotiations helped to make Grant’s name. When asked for terms his reply was ‘No terms except for an unconditional and immediate surrender can be accepted’. Buckner had no choose but to accept, and on 16 February his 12,000 men marched into captivity. ‘Unconditional Surrender’ Grant quickly became a celebrity in the north. He was promoted to major general, making him second in command in the west. Fort Donelson was the first major Union victory of the war. On 23 February Nashville fell to General Buell. Columbus, the western end of the Confederate line, was abandoned a few days later. Kentucky was secured for the Union, and most of west and central Tennessee captured. The capture of Forts Henry and Donelson began the pattern of steady Union progress in the west that was to slowly squeeze the life out of the Confederacy.