Rouge, 1,565; Plaquemine, 620, and Port Hudson, 9,409, it looks to me that all might be taken from Matagorda, or 2,000, if the place is of such importance that it should be held; from Baton Rouge one half might be taken, and 7,000 might be taken from Port Hudson. This is my judgment from here. It is of the first importance that we should hold Red River. This, you will observe, I have turned over to General Steele, in order that General Banks might have a greater number of troops to move with. If, however, General Steele Banks will have to supply the deficiency until re-enforcement can be got to General Steele. Already several regiments have gone to Little Rock to re-enforce him, probably 2,000 men, and when some troops ordered from Saint Louis to West Kentucky get through with the work of driving Forrest from the State, they, too, can be sent. The whole re-enforcement for General Steele, however, cannot be relied ont over 5,000 men. Fort Smith and the Indian Territory having been added to the Department of Arkansas may give General Steele sufficient additional troops as to materially strengthen him also.

General Banks has always been very vigilant in the organization of colored troops. It is to be hoped that his expedition up Red River will give a large number of recruits of this class. All acquired in this way, however, being without organization or discipline, could not be counted as so many men for defense of garrisons. Three of them, though, might count equal to one veteran soldier in fixing the number to leave behind at any one place. All plans for the attack on Mobile are left to General Banks. He will make his movements to take place elsewhere, it is not at all probable that the enemy can make any effort at raising the siege, if Mobile is once invested. Should the place be difficult to take from the number of troops held to defend it, the success of holding them there will be great.

You will remain with General Banks until his move from New Orleans is commenced and a landing effected at Pascagoula, or such place as may be selected bring to me, wherever I amy be, such report of operations as General Banks may then wish to forward. Write to me fully how you find matters immediately on your first interview with General Banks.

U. S. GRANT,

Lieutenant-General.

[Inclosure.]

CULPEPER COURT-HOUSE, VA., April 17, 1864.

Major General N. P. BANKS,

Commanding Department of the Gulf:

Owing to the difficulty of giving positive instructions to ad instant commander respecting his operations in the field, and being exceedingly anxious that the whole army should act nearly as a unit, I send Major-General Hunter, an officer of rank and experience, bearer of duplicate copy of instructions sent you, of the 31st of March,* together with written instructions for General Hunter's guidance in your and his interview.