Fought from February 12 through 16, 1862, the Union victory at Battle of Fort Donelson opened the Cumberland River as a pathway for federal invasion of the South in the Western Theater of the American Civil War.
Prelude to the Battle
At the onset of the American Civil War, the State of Tennessee comprised most of the northern border of the Confederate States of America in the West. Defending that border was difficult for the Confederacy because Union troops might use any of three major rivers (the Mississippi, which flows south to the Gulf of Mexico, and the Tennessee and Cumberland rivers, which flow north to the Ohio River) to invade the South.
In 1861, the State of Tennessee constructed earthen forts on the Tennessee and Cumberland rivers to prevent federal invasions from the north. Slaves and soldiers built Fort Donelson on a hill on the west bank of the Cumberland River near the Tennessee-Kentucky border. The fort had several shore batteries that defenders could use to fire on the river, a system of earthworks encircled it on the landside.
Grant Advances Against Fort Henry
By late 1861, President Abraham Lincoln was pressuring Union commanders in the West to invade the South. On January 30, 1862, the Western Theater commander, General Henry Halleck, reluctantly approved Brigadier General Ulysses S. Grant’s plan to attack Fort Henry, on the Tennessee River, just twelve miles west of Fort Donelson. Eager to move, Grant left Cairo, Illinois on February 2, with 15,000 soldiers, plus a flotilla of seven gunboats commanded by United States Navy Flag Officer Andrew Hull Foote. On February 6, Confederate Brigadier General Lloyd Tilghman surrendered Fort Henry after a seventy-five-minute bombardment by Foote’s gunboats.
Grant Advances Against Fort Donelson
Following the surrender of Fort Henry, Grant turned his attention to Fort Donelson. He marched his army toward the Cumberland River on February 12 and 13. After traversing the twelve-mile span between the two forts, Grant positioned his troops in a semi-circle around the western side of Fort Donelson.
Failed Naval Bombardment
On February 14, Foote’s flotilla traveled up the Cumberland River and attempted to reduce the fort with naval gunfire from the eastern side. The bombardment was ineffective, however, because the Confederates held the higher ground. Eventually, Foote’s gunboats withdrew, setting the stage for a land engagement.
After the fall of Fort Henry, General A. S. Johnston, the Confederate commander in the West, reinforced the garrison at Fort Donelson with 12,000 troops accompanied by generals Gideon J. Pillow, Simon B. Buckner, Sr., and John B. Floyd. Upon his arrival at Fort Donelson, Floyd assumed command of the 17,000-man garrison. Grant’s army had swollen to about 25,000 soldiers when reinforcements sent by Halleck arrived. Seeing that Grant had them surrounded, the Confederate generals attempted a breakout to avoid being trapped.
Failed Confederate Breakout
On the morning of February 15, Confederate troops surged out of the fort, attacking the Union right flank, commanded by Brigadier General John McClernand. The Rebels drove McClernand’s men back, but they did not rout them. By early afternoon, reinforcements from the Union center arrived and stabilized the situation.
Although a breakout was still possible, Pillow ordered his men back to their trenches to re-supply before making another attempt. Taking advantage of the delay, Grant ordered a counterattack on the left, forcing the Rebels back into a defensive position. By nightfall, the Federals reclaimed much of the ground they lost in the morning.
Floyd and Buckner Desert
During the night, the Confederate commanders concluded that their situation was hopeless. Fearing harsh reprisals for political acts they committed before the war, Floyd and Pillow turned the command over to Buckner and fled during the night to evade being captured.
The Federals awoke the next morning, surprised to see white flags of truce flying over Fort Donelson. Buckner requested an armistice and asked Grant for his terms of surrender. Grant replied, “No terms except unconditional and immediate surrender can be accepted.” Buckner had reason to believe that Grant would be more generous because of their personal relationship in the Union Army before the war. When Grant did not yield, Bucker could only capitulate to what he termed Grant’s “ungenerous and unchivalrous terms.”
Aftermath of the Battle
The Rebels suffered about 14,000 casualties at the Battle of Fort Donelson, compared with Union losses of about 2,500 men. However, the 12,000 prisoners inflated the Confederate losses.
Although the total casualty rate for both sides was small in comparison with later battles in the war, the fall of Fort Donelson was a serious blow to the Confederacy. It forced them to give up activities in Kentucky and move their operations deeper into Tennessee.
The victory also boosted faltering morale in the North. In the battle’s aftermath, “Unconditional Surrender” Grant became an instant celebrity, and army officials promoted him to major general, second-in-command in the West. Coupled with the capture of Fort Henry, the Union controlled two major waterways in the West from which to launch impending invasions of the South.