 Complete the following phrase:  At the outbreak of the Civil War, Lee joined the Union Army. Lee became a major in the 7th Kansas Cavalry, in October 1861. He was promoted to colonel of the regiment and took part in Henry W. Hallecks capture of Corinth, Mississippi. Shortly after the fall of that city, Lee commanded the 2nd Brigade in the Cavalry Division of the Army of the Mississippi and participated in the battle of Corinth. On November 29, 1862, he received a promotion to brigadier general in the Volunteer Army. He continued leading cavalry brigades in the Army of the Tennessee before he was appointed Chief-of-Staff to the XIII Corps under Maj. Gen. John A. McClerd. Lee served as chief-of-staff through much of the Vicksburg campaign, serving at the battles of Port Gibson, Champion Hill and 