FLAG-STEAMER PHILADELPHIA, Off Morris Island, September 26, 1863.

Major General Q. A. GILLMORE, U. S. Army,

Commanding Department of the South:

DEAR SIR: The rather limited means at my disposal for operating upon the interior lines of the harbor renders it very desirable that the enemy's resistance should be reduced as much as possible by whatever means you may possess.

If, therefore, you can complete the reduction of Sumter by your batteries on Cumming's Point, it would be of material assistance to me in the outset.

I have no doubt I could do this with the iron-clads, but so much of their power has already been expended, and so much will be required after passing Fort Sumter, that it will be highly important to spare them as much as possible.

With Sumter in our possession, the obstructions ranging from that work to Moultrie, whatever they are, would be removable with no great trouble and little risk, and I should advance upon the next series of defenses with the least possible expenditure of means, and with the iron-clads in the best condition.

May I ask, therefore, when your batteries may be able to operate on Sumter, and whether I may depend on your driving the enemy out of it? I shall be glad to contribute any cannon you may need to complete your works.

I think you will agree with me that it is good policy to pursue this curse, rather than to expend the monitors, of which I shall have only seven, and will need every one fully in attempting to make my way up the harbor.

I am, very respectfully, your obedient servant,

JNO. A. DAHLGREN,

Rear-Admiral, Commanding South Atlantic Blockading Squadron.

HEADQUARTERS DEPARTMENT OF THE SOUTH, In the Field, Morris Island, S. C., September 27, 1863.

Rear-Admiral JOHN A. DAHLGREN,
Commanding South Atlantic Blockading Squadron:

DEAR SIR: I have to acknowledge the receipt of your letter of yesterday, asking me at what time my "batteries may be able to operate on Sumter," and whether you can depend upon my "driving the enemy out of it," with a view to save the use of the monitors, of which" so much of their power has already been expended." I will open on Sumter at any time you are ready to move, event to-morrow morning, if you desire it.

I judge from the general tenor of your communication that the occupation of Sumter by us, or its evacuation by the enemy, is deemed essential in order to secure the removal of the channel obstructions between it and Sullivan's Island, and insure the success of the naval operations pending in this quarter. This is a condition newly imposed and somewhat grave in character.

That Fort Sumter possessed no power to harm the monitors in their passage up the harbor when our breaching batteries ceased firing on the 1st instant, is, I believe, generally conceded. At any

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