On 22 November, the 80th Illinois set out toward Chattanooga and arrived in the evening east of town. The next day, on 23 November, the regiment engaged with the enemy and took the first line of rifle splits as part of the XI Corps, driving on the left flank in the enemy's skirmishers. The 80th Illinois laid in line of battle all night. This advance was part of the Union Army of the Tennessee under Maj. Gen. William T. Sherman maneuvering to launch a surprise attack against Bragg's right flank on Missionary Ridge. Meanwhile, on 24 November, Eastern Theater troops on the opposite side of the line under Maj. Gen. Joseph Hooker defeated the Confederates in the Battle of Lookout Mountain and began a movement toward Bragg's left flank at Rossville.