1863-09-19: CHATTANOOGA. After their defeat at Chickamauga, Georgia, on Sept. 19-20, 1863, Union forces were besieged inside Chattanooga, Tennessee. Not until the end of November did they succeed, with the help of reinforcements, in driving off the Confederates. The most important engagements at Chattanooga were Orchard Knob, Lookout Mountain, Missionary Ridge and Rossville Gap. See individual listings of those battles for discussions of Wisconsin's participation. When Confederate forces withdrew on Nov. 27, 1863, Union leaders made Chattanooga the base for attacking Atlanta and moving east through the Confederacy during 1864. Fourteen Wisconsin units were active in and around Chattanooga: 1st, 10th, 15th, 18th, 21st, 24th, and 26th Infantry regiments; 3rd, 5th, 6th, 8th, 10th, and 12th Light Artillery batteries, and the 1st Heavy Artillery.