Chattanooga was the key to the whole strategic area of the upper Tennessee; for it was the best road, rail, and river junction between the lower Mississippi and the Atlantic ports of the South. It had been held for some time by a Federal garrison which had made it fairly strong. But toward the end of October it was short of supplies; and Hooker had to fight Longstreet at Wauhatchie in the Lookout Valley before it could be revictualed. When Hooker, Thomas, and Sherman were there together under Grant in November it was of course perfectly safe; and the problem changed from defense to attack. The question was how to drive Bragg from his commanding positions on Missionary Ridge and Lookout Mountain. The woods and hills offered concealment to the attack in some places. But Lookout Mountain was a splendid observation post, twenty-two hundred feet high and crested with columns of rock. The Ridge was three miles east, the Mountain three miles south, of Cameron Hill, which stood just west of Chattanooga, commanding the bridge of boats that crossed the Tennessee. The battle, fought with great determination on both sides, lasted three days--the twenty-third, twenty-fourth, and twenty-fifth of November. Sherman made the flank attack on Missionary Ridge from the north and Thomas the frontal attack from the west. Hooker attacked the western flank of Lookout Mountain. Thomas did the first day's fighting, which was all preliminary work, by advancing a good mile, taking the Confederate lines on the lower slopes of the Ridge, and changing their defensive features to face the Ridge instead of Chattanooga. At two the next morning Giles Smith's brigade dropped down the Tennessee in boats and surprised the extreme north pickets placed by Bragg at the mouth of the South Chickamauga to cover the right of the Ridge. By noon Sherman's men were over the Tennessee ready to coöperate with Thomas. Sherman had hidden his camp among the hills on the other side so well that his movements could not be observed, even from the commanding height of Lookout Mountain. The night surprise of Bragg's pickets and the drizzling rain of the morning prevented the Confederates from hearing or seeing anything of Sherman's attack in the early afternoon; so he found himself on the northern flank of Missionary Ridge before Bragg's main body knew what he was doing. When the Confederates did attack it was too late; and the twenty-fourth ended with Sherman entrenched against the flank on even higher ground than Thomas held against the center. Sherman's cavalry had meanwhile moved round the flank, on the lower level and much farther off, to cut Bragg's right rear connection with Chickamauga Station, whence the rails ran east to Cleveland, Knoxville, and Virginia.