A native of Kansas City, Gates was inducted into federal service in April 1941 at Fort Leavenworth, Kansas, and assigned to Headquarters and Service Troop, Tenth Cavalry. He attended OCS at Fort Knox, Kentucky, and received his commission in October 1942. Lt. Gates was then assigned to the 761st Tank Battalion, an all-Black unit, in December 1942, and was later promoted to battalion gunner officer.
He served in the European Theatre during four major campaigns and spent 183 consecutive days in combat. Additionally, he received a battlefield promotion to captain while serving in Europe during the war. With his experiences, he became the most decorated soldier in his unit, earning both a Silver Star Medal and a Bronze Star, in addition to a Purple Heart for wounds received in combat. He later commanded Company C. In the years after the war. He returned to Kansas City, where he worked for the 242nd Combat Engineer Battalion of the Missouri National Guard, which at one time was an all-Black unit.
He was named commander of the battalion at the rank of major and retired from the Missouri National Guard at the same rank.