Grant planned to have Sherman's Army of the Tennessee, assisted by the Army of the Cumberland, assault the northern end of Missionary Ridge, preparatory to rolling down it on the enemy's right flank. On November 23, Major General George Henry Thomas surprised the enemy in open daylight, advancing the Union lines and taking Orchard Knob, between Chattanooga and the ridge. The next day, Sherman failed to achieve his mission of getting atop Missionary Ridge, which was the key to Grant's plan of battle. Hooker's forces took Lookout Mountain using an ingenious maneuver to flank the enemy, in unexpected success. On the 25th, Grant ordered Major General George Henry Thomas to advance to the rifle-pits at the case of Missionary in an effort to help Sherman, after Sherman's army failed to take Missionary Ridge from the northeast. Four divisions of the Army of the Cumberland, with the center two led by Major General Philip Sheridan and Brigadier General Thomas J. Wood, chased the Confederates out of the rifle-pits at the base and, against orders, continued the charge up the 45-degree slope and captured the Confederate entrenchments along the crest, forcing a hurried retreat. The decisive battle gave the Union control of Tennessee and opened Georgia, the Confederate heartland, to Union invasion. Grant was given an enormous thoroughbred horse, "Cincinnati", by a thankful admirer in St. Louis.