[Inclosure.]

FLAG-SHIP A. McClernand, Commanding,&c.:

GENERAL: I have been down reconnoitering to-day. They have built extensive works and have guns in them. If left to themselves, they will but the other was out of range, and I could not get at them without bringing on a general engagement, which I am not prepared for to-day. I shall attack the forts in the morning, and I ask that you will send down men to hold them in case I do take them. The Price, Forest Queen, and the big barge will bring all that is required. The Forest Queen can carry artillery, which is indispensable to hold the hill. The men will capture tents enough without bringing any. This is a case where a dash will save everything. I drove the steamer that is supplying them up Big Black River; she had not time to land her supplies. Dispatch is

all-important at this moment.

Very truly,

DAVID D. PORTER.

SMITH'S PLANTATION, April 22, 1863-11 p. m.

Rear-Admiral DAVID D. PORTER, Comdg. Mississippi Squadron:

ADMIRAL: Your communication is this moment received. General Osterhaus is ordered to co-operate in the reduction and occupation of Grand Gulf. He will move an all the boats he can make available, at the earliest practicable moment. Re-enforcements will follow him as rapidly as I can send them. Of course, it will be expected that you will afford him, in occupying the place, the cover of your gunboats, until he shall have been sufficiently re-enforced against all hostile comers.

Colonel [Thomas S.] Mather, chief of my staff, bears this dispatch.

Your obedient servant,

JOHN A. McClernand.

CAMP AT MILLIKEN'S BEND, La., April 22, 1863.

Lieutenant Colonel John A. RAWLINS, U. S. Army,

Assistant Adjutant-General, Hdqrs. Dept. Of the Tennessee:

SIR: I have the honor to report, for the information of the commanding general that, pursuant to instructions, on the 17th instant I commenced firing upon the court-house and the railroad depot in Vicksburg with two 30-pounder Parrott rifles, placed in casemate battery opposite the town. The firing was continued at intervals during the daylight until the night of the 20th, with very unsatisfactory results on the first and SECOND days, the projectiles having been thrown with much inaccuracy, and having mostly fallen short of the town. On the THIRD the firing was better, and on the fourth day, though little effective, it was excellent, the shells apparently bursting at the height and distance of the dome of the court-house, and at the very center of the ridge pole of the depot, the elevations used being 15 and 10 degrees, respectively. Still, the result of the firing, as that of siege artillery, has not been effective. The enemy seems to have quitted the use of the depot on the THIRD day. In the night of the 20th, pursuant to instructions, I removed to the landing, and so soon as a steamer arrived,