On Wednesday, the 29th of April, a part of the gunboat fleet under Admiral Porter, consisting of the Benton (flagship), Lafayette, Mound City, Pittsburg, Carondolet, Tuscumbia and Louisville, left Hard Times, and steaming down below Coffee Point, engaged the rebel batteries at Grand Gulf, just at the confluence of the Big Black and the Mississippi. The engagement commenced at eight o’clock and lasted until half-past two. The enemy had four batteries at Grand Gulf, one on the rock around which the waters of the Big Black flow into the Mississippi, and three below, about midway between the water and the summit of the bluffs. In the former they had placed four heavy guns, and in the three latter two and three each, with parapets, embrasures and rifle pits. The upper guns were very large, throwing shot and shell weighing one hundred pounds. The lower guns were mostly thirty-two-pounders. The Benton opened the fight, followed by the other gunboats in rapid succession. At first they stood off at long range, and fired at a distance of a mile or more; but as the fire became warm they pressed closely to the bluff, and passed and repassed the batteries, sending broadsides upon the fort whenever they came in position. For six hours where the gunboats firing and receiving fire, until the gradually ceasing explosions of the enemy indicated their desire to terminate the engagement. The Benton suffered considerably in her upper works, not less than a half dozen shots passing entirely through her. One shell exploded in her porthole, killing five men. The Tuscumbia was disabled. Other gunboats were more or less injured, but not seriously. On the same day Admiral Porter sent the following report to the Secretary of the Navy: HON. GIDEON WELLES, Secretary of the Navy:— I have the honor to inform you that, by an arrangement with General Grant, I attacked the batteries at Grand Gulf this morning, which were very formidable. After a fight of five hours and thirty minutes we silenced the lower batteries, but failed to silence the upper one, which was high, strongly built, and had guns of very heavy calibre. The vessels were unmanageable in the heavy current. It fired but feebly toward the last, and the vessels all laid by and enfiladed it, while I went up a short distance to communicate with General Grant, who concluded to land the troops and march over to a point two miles below Grand Gulf. I sent the Lafayette back to engage the upper batteries, which she did, and drove the soldiers out of it, as it did not respond after a few fires. At six p. m. we attacked the batteries again, and under cover of the fire all the transports passed by in good condition. The Benton, Tuscumbia, and Pittsburg were much cut up, having twenty-four killed and fifty-six wounded, but they are all ready for service. We land the army in the morning on the other side to march on Vicksburg.