HEADQUARTERS WESTERN DEPARTMENT,
Bowling Green, Ky., February 8, 1862.

Hon. J.P. BENJAMIN,
Secretary of War:

SIR: No reliable particulars of the loss of Fort Henry have yet reached me. This much, however, is known, that nearly all of the force at Fort Henry retreated to Fort Donelson, and it is said that General Tilghman and about 80 officers and men surrendered in the fort.

The capture of that fort by the enemy gives them the control of the navigation of the Tennessee River, and their gunboats are now ascending the river to Florence. Operations against Fort Donelson, on the Cumberland, are about to be commenced, and that work will soon be attacked. The slight resistance at Fort Henry indicates that the best open earthworks are not reliable to meet successfully a vigorous attack of iron-clad gunboats, and, although now supported by a considerable force, I think the gunboat of the enemy will probably take Fort Donelson without the necessity of employing their land force in co-operation, as seems to have been done at Fort Henry.

Our force at Fort Donelson, including the force from Fort Henry and three regiments of General Floyd's command, is about 7,000 men, not well armed or drilled, except Heiman's regiment and the regiments of Floyd's command. General Floyd's command and the force from Hopkinsville is arriving at Clarksville, and can, if necessary, reach Donelson in four hours by steamers which are there.

Should Fort Donelson be taken, it will open the route to the enemy to Nashville, giving them the means of breaking the bridges and destroying the ferry-boats on the river as far as navigable.

The occurrence of the misfortune of losing the fort will cut off the communication of the force here under General Hardee from the south bank of the Cumberland. To avoid the disastrous consequences of such an event I ordered General Hardee yesterday to make, as promptly as it could be done, preparations to fall back to Nashville and cross the river. 

The movements of the enemy on my right flank would have made a retrograde in that direction to confront the enemy indispensable in a short time. But the probability of having the ferriage of this army corps across the Cumberland intercepted by the gunboats of the enemy admits of no delay in making the movement.

Generals Beauregard and Hardee are, equally with myself, impressed with the necessity of withdrawing our force from this line at once. 

With great respect, your obedient servant,

A. S. JOHNSTON,

 General, C. S. Army.