Grant had no instructions to attack Fort Donelson, but he had none forbidding him to do it. He straightway moved nearly his whole force over the eleven miles of dreadful roads, and on the 12th began investing the stronghold, an earthwork inclosing about 100 acres, with outworks on the land and water sides, and defended by more than 20,000 men commanded by General Floyd, who had been President Buchanan's Secretary of War. The investing force had its right near the river above the fort. The weather was alternately wet and freezing cold. The troops had no shelter, and suffered greatly. On the 14th, without serious opposition, the investment was completed. At three o'clock in the afternoon of the 14th, flag officer Foote began the attack, the fleet of gunboats steaming up the river and firing as rapidly as possible; but several were disabled by the enemy's fire, and all had to fall back before nightfall. The enemy telegraphed to Richmond that a great victory had been achieved.
On the next day, Grant, riding several miles to the river, met Foote on his gunboat, to which he was confined by a wound received the day before. Returning, he found that a large force from the fort had made a sortie upon a part of his line, but had been driven back after a severe contest. It was found that the haversacks of the Confederates left on the field contained three days' rations. Instantly, Grant reasoned that the intention was not so much to drive him away as to break through his line and escape. He ordered a division that had not been engaged to advance at once, and before night it had established a position within the outer lines of defense. Surrender or capture the next day was the fate of the Confederates.
During the night General Floyd and General Pillow, next in command, and General Forest made their escape with about 4000 men. Before light the next morning, General Grant received a note from General S. B. Buckner, who was left in command of the fort, suggesting the appointment of commissioners to agree upon terms of capitulation, and meanwhile an armistice until noon. To this note General Grant sent the curt reply: "No terms except an unconditional and immediate surrender can be accepted. I propose to move immediately upon your works." General Buckner sent back word that he was compelled by circumstances "to accept the ungenerous and unchivalrous terms" which had been proposed.
This victory electrified the whole North, then greatly in need of cheer. General Grant became the hero of the hour. His name was honored and his exploit lauded from one end of the country to the other. It was not yet a year since he had been an obscure citizen of an obscure town. Already many regarded him as the nation's hope. A phrase from his note to General Buckner was fitted to his initials, and he was everywhere hailed as "Unconditional Surrender" Grant.
In this campaign he first revealed the peculiar traits of his military genius, clear discernment of possibilities, comprehension of the requirements of the situation, strategical instinct, accurate estimate of the enemy's motive and plan, sagacious promptness of action in exigencies, staunch resolution, inspiring energy, invincible poise. For his achievement he was promoted to be a major-general of volunteers. He had found himself now.