Grant's seventh (and first successful) effort to get a foothold (from which to carry out one of the boldest and most brilliant operations recorded in the history of war) began with a naval operation on the sixteenth of April, when Porter ran past the Vicksburg batteries by night. Though Porter had the four-knot current in his favor he needed all his skill and moral courage to take a regular flotilla round the elongated U made by the Mississippi at Vicksburg, with such a bend as to keep vessels under more or less distant fire for five miles, and under much closer fire for nearly nine. At the bend the vessels could be caught end-on. For nearly five miles after that they were subject to a plunging fire. Porter led the way on board the flagship _Benton_. He had seven ironclads, of which three were larger vessels and four were gunboats built by Eads, a naval constructor with orignal ideas and great executive ability. One ram and three transports followed. Coal barges were lashed alongside or taken in tow. Some of these were lost and one transport was sunk. But the rest got through, though not unscathed. It seemed like a miracle to the tense spectators that any flotilla should survive this dash down a river of death flowing through a furnace. But the ironclads, magnificently handled, stood up to their work unflinchingly, fired back with regulated vigor, and took their terrific pounding without one vital wound. Porter presently relieved Farragut, who went back to New Orleans. From this time, till after the fall of Vicksburg and Port Hudson, Porter commanded three flotillas, each with a base of its own: first, a flotilla remaining north of Vicksburg for work on the Yazoo; secondly, the main body between Vicksburg and Grand Gulf; thirdly, the Red River flotilla. This combined naval force commanded all lines of communication north, south, and west of Vicksburg, thus enabling Grant to concentrate entirely against the eastern side. On the thirtieth of April Grant landed with twenty thousand men at Bruinsburg, on the east side of the Mississippi, about sixty miles below Vicksburg. A week later Sherman reinforced him to thirty-three thousand. Before the fall of Vicksburg his total strength reached seventy-five thousand. The Confederate total also fluctuated; but not so much. There were about sixty thousand Confederates in the whole strategic area between Vicksburg and Jackson (fifty miles east) when Grant made his first daring move, and about the same when Vicksburg surrendered. The scene of action was almost triangular; for it lay between the three lines joining Jackson, Haynes's Bluff, Rodney, and Jackson again. The respective lengths of these straight lines are forty, fifty, and seventy miles. But roundabout ways by land and water multiplied these distances, and much fighting and many obstacles vastly increased Grant's difficulties.