WASHINGTON, D. C., April 18, 1863.

Major-General BANKS, New Orleans:

GENERAL: Last advices from General Grant state that he was in possession of New Carthage, and hoped soon to get sufficient forces and transports past Vicksburg to attack Grand Gulf, and perhaps co-operate with you against Port Hudson. I need not remind you of the importance of making every effort to open communication with him and Admiral Farragut.

I have carefully examined your instructions of the 27th to Col. S. B. Holabird. The Government had already been fully informed by you of most matters contained in those instructions. If we could possibly have given you what you asked we should have done so long ago. You were told before you left here what we could give you. We have done that and even more. We must re-enforce and strengthen the most important and exposed points. Others, although in themselves important, must wait. Large numbers of troops and transports were sent to General Hunter to assist Admiral DuPont in his operations against Charleston. I was supposed at the time that these operations would have been terminated long ago and that the transports, iron-clads, and troops would have been sent to the Mississippi. The result has not equaled expectations, and everything is still detained there by orders of the President. The military forces there merely act as auxiliary to the Navy, and are entirely dependent upon the movement of Admiral DuPont. Should he succeed in his next attack or determine not to renew it, both transports and troops, and, I hope, also iron-clads, will be available for operations on the Mississippi.

The court at New Orleans was organized was organized under the auspices of the State Department, and the Secretary of War has not been advised what duties were assigned to it or to its officers. In this matter, however, general principles must govern.

Louisiana is essentially hostile territory, in the military occupation of the United States. The common laws and usages of war must govern.

You represent the power of this Government in that department, and must necessarily control all military operations there. Neither this court nor its officers should be permitted to interfere with or embarrass your movements. If it becomes necessary to seize transportation, provisions, &c., for the use of your army or the success of your operations, you will do so without any regard to this court or its officers. Moreover, if they interfere with your operations in the field, send them back to the city, or, if necessary, out of the department.

The War Department has given you full power, and you have only to exercise it with discretion and justice.

Very respectfully, your obedient servant,

H. W. HALLECK,

General-in-Chief.

DEPARTMENT OF THE GULF,

United States Military Telegraph Office, New Orleans,

Ciote Gelee, near Vermillionville, April 18, 1863.

Brigadier General THOMAS W. SHERMAN:

Please send the following to the general-in-chief:

I beg leave, at the risk of being considered importunate, to repeat my earnest request that more cavalry may be sent to this department. Every day but confirms