After the fall of Confederate-held Fort Henry on the Tennessee River to the Union on February 6, 1862 (largely thanks to Union gunboats), thousands of rebel troops were sent to reinforce the larger Fort Donelson, which was located 10 miles away on the Cumberland River—another key gateway to the Confederacy. On February 13, one of Ulysses S. Grant’s (1822-85) officers, Brigadier General John McClernand (1812-1900), initiated the Battle of Fort Donelson when he tried unsuccessfully to capture a rebel battery along the fort’s outer works.

Over the next three days, Grant tightened the noose around Fort Donelson by moving a flotilla up the Cumberland River to shell the fort from the east. On February 15, the Confederates tried to break out of the Yankee perimeter. An attack on the Union right flank and center sent the Yankees back in retreat, but then Confederate General Gideon Pillow (1806-78) made a fatal miscalculation. Rather than retreating from the fort and escaping to safety, he opted to pull his men back into their entrenchments. In response, Grant launched a fierce counterattack and regained much of the ground that had been ceded. The Confederates were surrounded, with their backs to the Cumberland River. Only several thousand troops managed to escape before Fort Donelson was surrendered on February 16.

Of the approximately 16,000 Confederates who had engaged in battle, more than 12,000 were captured or missing, while approximately 1,400 others were wounded or killed. Of the estimated 24,500 Union troops who fought at Fort Donelson, total casualties were around 2,700.

When the rebels asked for terms of surrender, Grant replied that no terms “except unconditional and immediate surrender” would be acceptable. This earned him the nickname “Unconditional Surrender.” President Abraham Lincoln (1809-65) promoted Grant to major general after the battle.

The Battle of Fort Donelson was the first major Union victory in the Civil War and a major victory for Ulysses S. Grant. The losses of Fort Henry and Fort Donelson were disasters for the Confederates. Kentucky was lost and Tennessee lay wide open to the Yankees. The Cumberland River and Tennessee River became integral parts of Union supply lines. Nashville would fall to Union troops within a matter of days.

Fort Donelson National Battlefield is now part of the National Park Service. The entrance to the park is in Dover, Tennessee, though parts of the battlefield extend to Kentucky.