 In his capacity as chief engineer of the XXIII Corps, he was a key factor in the defense of Knoxville, Tennessee.This city was successfully defended against a siege led by Confederate Lt. Gen. James Longstreet, which culminated in the November 29, 1863, Battle of Fort Sanders.Due to Poe's contributions, Maj. Gen. William T. Sherman selected Poe as his chief engineer in 1864.