NASHVILLE, April 6, 1863.

Lieutenant Colonel C. GODDARD,

Assistant Adjutant-General:

The gunboat commanders have issued orders to leave at 3 a.m. to-morrow. I have notified them of the order of General Rosecrans that they should wait for orders, but they seem to pay no attention to it. The river is falling rapidly, and large boats may be caught here.

ROBT. B. MITCHELL,

Brigadier-General.

HEADQUARTERS TWENTY-FIRST ARMY CORPS,
Murfreesborough, Tenn., April 6, 1863.

Brigadier General JAMES A. GARFIELD,

Chief of Staff:

SIR: On more than one occasion I have had some brief conversation with the commanding general in regard to the enterprise proposed by Colonel Streight, Fifty-first Indiana Volunteers, for cutting the enemy's communications in his rear. This is certainly a most important movement, and, if it could be crowned with anything like a reasonable amount of success, would undoubtedly lead to great results. But I do not propose in this communication to discus the propriety of attempting the enterprise. That is a question which the commanding general, as the responsible head of this army, must and will decide, weighing well the rational probabilities of success against of failure.

My object is respectfully to offer some suggestions, supposing the commanding general should decide Colonel Streight's scheme to be feasible, as to the time it should be made in reference to any forward movement of this army, and especially and earnestly to urge that Colonel Streight's enterprise, if made, should be undertaken sufficiently in advance of any forward movement of this army as to permit the accomplishment of his mission before the movement on the following considerations:

This conclusion is based on the following considerations:

I take it or granted this army will not, certainly it ought not, to advance until it is sufficiently re-enforced and strengthened, after deducting all the garrisons which it will necessarily have to leave to guard its communications, to place its success, should it encounter the rebel army, beyond a reasonable doubt. The encounter of two armies, equal in strength, or so nearly so as to allow, is simply a prize fight, yielding the victor little more than the ground he stands on, and by no means compensating for the expediture of human life necessary to obtain the result. Our advance should be made with such overwhelming numbers as would certainly lead to one of two important results: First, that if, by skillful maneuvering, we should succeed in bringing the enemy to an engagement, a complete and perfect victory, accompanied by the destruction of his army, would be our reward; or, secondly, he would be compelled to abandon the whole of the fertile plains of Middle Tennessee to our occupation. If we should advance with a force not sufficiently strong to place success beyond a reasonable doubt, we should simply expose ourselves to defeat. On the contrary, should our advance be made with a force placing our success beyond a reasonable doubt, one of the two results already suggested would necessarily ensue.

It is almost certain the enemy would retire into the mountainous region of Southeastern Tennessee and around Chattanooga. In this region, with his lines of communication, by which his supplies would be drawn, protected, he could defy us for an indefinite time, and, after