Fort Donelson rose in early 1862 on the west bank of the Cumberland River, near the hamlet of Dover, Tennessee. Confederate engineer Bushrod Johnson selected the site and supervised construction: a few acres of log huts enclosed by rifle pits dug along a ridgeline and breastworks curving in a three-mile arc from the river bluff on the north to Dover on the south. Cannons crowned the hundred-foot bluff -- a 128-pounder and two 32-pounders aimed downriver, ready to shred anything that tried to pass. Workers from the nearby Cumberland Iron Works did much of the heavy labor. The fort was designed to work in tandem with Fort Henry, ten miles west on the Tennessee River, forming a twin-fortress shield across the rivers that led into the heart of the Confederacy.

Grant had orders from General Henry Halleck to take Fort Donelson by February 8. He sized up the terrain and knew that deadline was impossible. Fort Henry, the companion fortress on the Tennessee River, had already fallen to Union forces on February 6, but Donelson was better positioned and more heavily defended. Grant assembled three brigades under Brigadier Generals John A. McClernand, Charles F. Smith, and Lew Wallace -- the same Lew Wallace who would later write Ben-Hur. Flag Officer Andrew Foote brought his gunboats up the Cumberland to assault from the water. The siege began on February 12 with skirmishing along the Confederate perimeter. On February 14, Foote's ironclad flotilla attacked the river batteries and was badly mauled, the naval guns no match for the elevated Confederate cannon.

On the morning of February 15, the Confederates launched a desperate breakout attempt, smashing into McClernand's division and briefly opening the road to Nashville. But confusion and indecision among the Confederate commanders -- Bushrod Johnson, Gideon Pillow, and John Floyd held command in rapid succession -- squandered the advantage. When Grant arrived on the field and learned of the breakout, he ordered an immediate counterattack. Charles F. Smith led his division in a bayonet charge that carried the outer Confederate works. By evening, the Confederates were penned in again, worse off than before. Floyd, a former U.S. Secretary of War who feared hanging if captured, escaped by steamboat with his Virginia brigade. Pillow fled with him. Cavalry commander Nathan Bedford Forrest led his horsemen through the icy backwaters to freedom. The task of surrender fell to the last man standing: Simon Bolivar Buckner, an old friend of Grant's from West Point.

The fall of Fort Donelson electrified the Union. The war had been going badly in Virginia, and the western theater offered little hope until Grant's twin victories at Henry and Donelson cracked the Confederate defensive line wide open. Nashville fell without a fight two weeks later, making Tennessee the first Confederate state capital to be captured. Grant became a national hero overnight. Newspapers seized on his surrender demand and christened him "Unconditional Surrender Grant" -- initials that conveniently matched his name. The strategic logic was clear: control the rivers, divide the Confederacy, win the war. It was a strategy Grant would pursue all the way to Appomattox.

After the front line moved south, Fort Donelson settled into quiet garrison duty. One last Confederate attempt to retake it came on August 25, 1863, when 785 Confederate soldiers attacked the 404-man Union garrison of the 71st Ohio Regiment. After suffering 30 casualties, the attackers retreated and were chased off by the Fifth Iowa Cavalry. The Fort Donelson National Battlefield was established in 1928, listed on the National Register of Historic Places on October 15, 1966, and redesignated as a national battlefield in 1985. Today the earthworks, rifle pits, and river batteries remain visible along the bluffs above the Cumberland, a quiet stretch of Tennessee countryside where a future president first proved he could fight.