Sanderson enlisted as a Private in the 15th U.S. Infantry on October 24, 1861. His father John P. Sanderson was already a lieutenant colonel of this regiment serving form from May 14, 1861 until July 4, 1863. He was commissioned 2nd Lieutenant on October 31, 1861. He received a brevet as 1st Lieutenant on April 7, 1862, for gallant and meritorious service in the Battle of Shiloh Tennessee. He was promoted to 1st Lieutenant in the Regular Army on November 9, 1862. Sanderson received a second brevet as captain on September 1, 1864, for gallant and meritorious service during the Atlanta Campaign.