The one extraordinary incident of the expedition was the disabling of the _Mound City_, one of the ironclad gunboats, and the great loss of life that it occasioned. When near St. Charles the troops under Fitch were landed, and the _Mound City_ moving up the river, was fired on by concealed batteries under the direction of Lieutenant Dunnington. A 32-pound shot struck the vessel, crashed through the side and passed through the steam-drum. The steam filled the vessel in an instant. Many of the men were so quickly enveloped in the scalding vapor that they had no chance to escape. Others leaped overboard, some being drowned and some rescued through the efforts of the _Conestoga_ which was lying near. While straining every nerve to save their lives, the men had to endure a shower of bullets from Confederate sharpshooters on the river banks. Of the one hundred and seventy-five officers and men of the _Mound City_ only twenty-five escaped death or injury in that fearful catastrophe. Meanwhile, Colonel Fitch with his land forces rushed upon the Confederate batteries and captured them. The unfortunate vessel was at length repaired and returned to service. For some time it had been known in Federal military and naval circles that a powerful ironclad similar to the famous _Monitor_ of Eastern waters was being rushed to completion up the Yazoo. The new vessel was the _Arkansas_. On July 15th, she steamed through the Union fleet, bravely exchanging broadsides, and lodged safely under the guns of Vicksburg. That evening the Federal boats in turn ran past the doughty _Arkansas_, but failed to destroy her. The month of July had not been favorable to the Federal hopes. Farragut had returned to New Orleans. General Williams had gone with him as far as Baton Rouge. Davis now went with his fleet back to Helena. Halleck was succeeded by Grant. Vicksburg entered upon a period of quiet. But this condition was temporary. The city's experience of blood and fire had only begun. During the summer and autumn of 1862, the one thought uppermost in the mind of General Grant was how to gain possession of the stronghold. He was already becoming known for his bull-dog tenacity. In the autumn, two important changes took place, but one day apart. On October 14th, General John C. Pemberton succeeded Van Dorn in command of the defenses of Vicksburg, and on the next day David D. Porter succeeded Davis as commander of the Federal fleet on the upper Mississippi. So arduous was the task of taking Vicksburg that the wits of General Grant, and those of his chief adviser, General W. T. Sherman, were put to the test in the last degree to accomplish the end. Grant knew that the capture of this fortified city was of great importance to the Federal cause, and that it would ever be looked upon as one of the chief acts in the drama of the Civil War.