On the promotion of Halleck to the command of all the armies of the North, with headquarters at Washington, Grant was left in superior command in the West and the great task before him was the capture of the "Gibraltar of the West." Vicksburg might have been occupied by the Northern armies at any time during the first half of the year 1862, but in June of that year General Bragg sent Van Dorn with a force of fifteen thousand to occupy and fortify the heights. Van Dorn was a man of prodigious energy. In a short time he had hundreds of men at work planting batteries, digging rifle-pits above the water front and in the rear of the town, mounting heavy guns and building bomb-proof magazines in tiers along the hillsides. All through the summer, the work progressed under the direction of Engineer S. H. Lockett, and by the coming of winter the city was a veritable Gibraltar. From the uncompleted batteries on the Vicksburg bluffs, the citizens and the garrison soldiers viewed the advance division of Farragut's fleet, under Commander Lee, in the river, on May 18, 1862. Fifteen hundred infantry were on board, under command of General Thomas Williams, and with them was a battery of artillery. Williams reconnoitered the works, and finding them too strong for his small force he returned to occupy Baton Rouge. The authorities at Washington now sent Farragut peremptory orders to clear the Mississippi and accordingly about the middle of June, a flotilla of steamers and seventeen mortar schooners, under Commander D. D. Porter, departed from New Orleans and steamed up the river. Simultaneously Farragut headed a fleet of three war vessels and seven gunboats, carrying one hundred and six guns, toward Vicksburg from Baton Rouge. Many transports accompanied the ships from Baton Rouge, on which there were three thousand of Williams' troops. The last days of June witnessed the arrival of the combined naval forces of Farragut and Porter below the Confederate stronghold. Williams immediately disembarked his men on the Louisiana shore, opposite Vicksburg, and they were burdened with implements required in digging trenches and building levees. The mighty Mississippi, at this point and in those days, swept in a majestic bend and formed a peninsula of the western, or Louisiana shore. Vicksburg was situated on the eastern, or Mississippi shore, below the top of the bend. Its batteries of cannon commanded the river approach for miles in either direction. Federal engineers quickly recognized the strategic position of the citadel on the bluff; and also as quickly saw a method by which the passage up and down the river could be made comparatively safe for their vessels, and at the same time place Vicksburg "high and dry" by cutting a channel for the Mississippi through the neck of land that now held it in its sinuous course.