ATTACK ON FORT DONELSON BY THE FEDERAL GUNBOATS. ] [Illustration: THE SURRENDER OF FORT DONELSON. ] The relative positions of Fort Henry and Donelson, the former on the Tennessee river and the latter on the Cumberland, should be clearly understood, in order to comprehend the difficulties of this undertaking. Fort Henry had been occupied by Federal troops, and it became necessary to effect the reduction of Fort Donelson, in order to open the river to the navigation of the national flotilla, and to reach Nashville, the capital of Tennessee. The surrender of Fort Henry took place on the 6th of February. One of the gunboats, the Essex, being disabled, was obliged to return to Cairo for repairs, while the Lexington, Conestoga and Tyler, returned to the Ohio, in order to reach the Cumberland river to make the ascent to Fort Donelson. Commodore Foote having completed his preparations, left Cairo on the 11th of February for the scene of action—the Carondelet having previously been sent forward to reconnoitre the position. On the same day General Grant issued his orders for the movement of the land forces in two divisions, on the following morning. The distance from Fort Henry to Fort Donelson across the land lying between the two rivers, is fourteen miles. There are several roads running from Fort Henry to Dover, near which Fort Donelson was situated. The divisions were disposed by brigades, one of which was to be thrown into Dover to cut off the retreat of the enemy, if attempted by that route. Fort Donelson takes its name from Andrew Jackson Donelson, a citizen of Tennessee, and its construction was commenced as early as May, 1861. It occupied the best position for defence on the Cumberland river, standing on the summit of a fine slope, rising to the height of one hundred and fifty feet from the river, on its right bank, and mounted sixteen guns. There were two water batteries, one of which was about twenty or thirty feet above the river, and defended by nine pieces, eight thirty-two-pound guns, and one ten-inch columbiad. The second was some sixty feet above, and was mounted with one ten-inch columbiad, and two thirty-two pound carronades. Both these batteries were sunken or excavated in the hill-side. In the lower one, strong traverses were left between the guns, to secure them against an enfilading fire. The elevation above the water at the time of the gunboat attack, gave them a fine command of the river, and made the task of attacking them in front an arduous one. The range of the guns in arc, was, however, quite limited. The third occupied the summit of the hill, and mounted four 128-pound guns. The camp was behind the fort on the hill, but within range of gunboats on the river. THE NAVAL ATTACK.