was on sick leave. He was temporarily assigned to the staff of General George B. McClellan in Ohio. After recovering, he transferred back to the Regiment of Mounted Riflemen where he was promoted to captain in May 1861. As an adjutant of General Samuel D. Sturgis he saw action at the Battle of Dug Springs and observed the Union defeat at Wilson's Creek in August 1861 in Missouri, serving as a staff officer to General Nathaniel Lyon. Granger was cited for gallantry at Wilson's Creek, became a brevet major and was made a commander of the St. Louis Arsenal. In November 1861, Granger assumed command of the 2nd Michigan Cavalry Regiment at Benton Barracks in St. Louis, becoming a colonel of volunteers. One of the Union veterans wrote in a memoir that Granger's "military genius soon asserted itself by many severe lessons to the volunteer officers and men of this regiment. He brought them up to the full standard of regulars within a period of three months," and "though a gruff appearing man, had succeeded in winning the respect of his regiment by his strict attention to all the details of making a well disciplined body of soldiers out of a mass of awkward men from every walk of life." In February 1862, on the orders of General John Pope, the 2nd Michigan proceeded from St. Louis to Commerce, Missouri, where Pope assembled nearly 20,000 Union troops for an advance on New Madrid, Missouri. Granger assumed command over the Third Cavalry Brigade consisting of the 2nd and the 3rd Michigan cavalry regiments. After the 7th Illinois joined the brigade, it was reorganized into a cavalry division. On March 26, 1862, Granger was promoted to brigadier general of volunteers and commanded the Cavalry Division, Army of the Mississippi during the Battle of New Madrid and the Siege of Corinth. He was promoted to major general of volunteers on September 17, 1862, and took command of the Army of Kentucky. He conducted cavalry operations in central Tennessee before his command was merged into the Army of the Cumberland, becoming the Reserve Corps. Granger is most famous for his actions commanding the Reserve Corps at the Battle of Chickamauga. There on September 20, 1863, the second day of the battle, he reinforced, without orders, Major General George H. Thomas' XIV Corps on Snodgrass Hill by ordering James B. Steedman to send two brigades