Fort Henry had been an easy victory.  The rebel commander, convinced that he could not defend the place, had early that morning sent away his garrison of three thousand on a retreat to Fort Donelson, and simply held out during a two hours’ bombardment until they could escape capture.  To take Fort Donelson was a more serious enterprise.  That stronghold, lying twelve miles away on the Cumberland River, was a much larger work, with a garrison of six thousand, and armed with seventeen heavy and forty-eight field guns.  If Grant could have marched immediately to an attack of the combined garrisons, there would have been a chance of quick success.  But the high water presented unlooked-for obstacles, and nearly a week elapsed before his army began stretching itself cautiously around the three miles of Donelson’s intrenchments.  During this delay, the conditions became greatly changed.  When the Confederate General Albert Sidney Johnston received news that Fort Henry had fallen, he held a council at Bowling Green with his subordinate generals Hardee and Beauregard, and seeing that the Union success would, if not immediately counteracted, render both Nashville and Columbus untenable, resolved, to use his own language, “To defend Nashville at Donelson.”

An immediate retreat was begun from Bowling Green to Nashville, and heavy reinforcements were ordered to the garrison of Fort Donelson.  It happened, therefore, that when Grant was ready to begin his assault the Confederate garrison with its reinforcements outnumbered his entire army.  To increase the discouragement, the attack by gunboats on the Cumberland River on the afternoon of February 14 was repulsed, seriously damaging two of them, and a heavy sortie from the fort threw the right of Grant’s investing line into disorder.  Fortunately, General Halleck at St. Louis strained all his energies to send reinforcements, and these arrived in time to restore Grant’s advantage in numbers.

Serious disagreement among the Confederate commanders also hastened the fall of the place.  On February 16, General Buckner, to whom the senior officers had turned over the command, proposed an armistice, and the appointment of commissioners to agree on terms of capitulation.  To this Grant responded with a characteristic spirit of determination:  “No terms except unconditional and immediate surrender can be accepted.  I propose to move immediately upon your works.”  Buckner complained that the terms were ungenerous and unchivalric, but that necessity compelled him to accept them; and Grant telegraphed Halleck on February 16:  “We have taken Fort Donelson, and from twelve to fifteen thousand prisoners.”  The senior Confederate generals, Pillow and Floyd, and a portion of the garrison had escaped by the Cumberland River during the preceding night.

Since the fall of Fort Henry on February 6, a lively correspondence had been going on, in which General Halleck besought Buell to come with his available forces, assist in capturing Donelson, and command the column up the Cumberland to cut off both Columbus and Nashville.  President Lincoln, scanning the news with intense solicitude, and losing no opportunity to urge effective cooeperation, telegraphed Halleck: