The battery was not directly engaged in either of the major engagements at Liberty Gap or Hoover's Gap. In General Braxton Bragg's report on the Organization of troops in Department No 2, on July 31, 1863, Calvert's Arkansas Battery, under the command of Lieutenant Key, was listed as assigned to Brigadier General L.E. Polk's Brigade of Major General Patrick R. Cleburne's Division or Lieutenant General D.H. Hill's Army Corps. The battery was still assigned to Polk's brigade in the August 10, 1863 report on the organization of troops in the Department of Tennessee. During the Battle of Chickamauga, Calvert's Arkansas Battery, under the Command of Lieutenant Key was assigned to an artillery battalion consisting of Douglas Texas Battery and Semple's Alabama Battery, under the command of Major T.R. Hotchkiss. The battalion supported Major General Cleburne's Division of Lieutenat General D.H. Hill's Corps of the Army of Tennessee. On October 6, 1863, Lieutenant Key provided a report on the battery's roll in the battle:  The Chattanooga Campaign was a series of maneuvers and battles in October and November 1863, during the American Civil War. Following the defeat of Maj. Gen. William S. Rosecrans' Union Army of the Cumberland at the Battle of Chickamauga in September, the Confederate Army of Tennessee under Gen. Braxton Bragg besieged Rosecrans and his men by occupying key high terrain around Chattanooga, Tennessee. Ulysses S. Grant was given command of Union forces in the West and significant reinforcements began to arrive with him in Chattanooga from Mississippi and the Eastern Theater. The Union Army of the Tennessee under Maj. Gen. William T. Sherman maneuvered to launch a surprise attack against Bragg's right flank on Missionary Ridge. On November 25, Sherman's attack on Bragg's right flank at Tunnel Hill on the east end of Missionary Ridge, which was defended by Cleburne's Division, with Calvert's Arkansas Battery. Lieutenant Key and the battery were praised in Cleburne's report of the battle. Hoping to distract Bragg's attention, Grant authorized Thomas's army to advance in the center of his line to the base of Missionary Ridge. A combination of misunderstood orders and the pressure of the tactical situation caused Thomas's men to surge to the top of Missionary Ridge, routing the Army of Tennessee, which retreated to Dalton, Georgia, fighting off the Union pursuit successfully at the Battle of Ringgold Gap.