William C. "Bill" Mitchell Jr. enlisted in the Army in 1945, serving one year following World War II. Shortly after being discharged from the Army, he joined the 179th Infantry Regiment of the Oklahoma Army National Guard, moving with the Guard to the front lines in Korea. There he served in the medical field, demonstrated outstanding leadership in medical treatment and evacuation, with emphasis upon helicopter evacuation from front-line aid stations to MASH hospitals.
Rejoining the Guard following separation from the Army, he was appointed a second lieutenant as a medical assistant, but shortly afterwards resigned his commission to be appointed a warrant officer. In his long term of duty with the Guard he showed such exceptional devotion and dedication to his assignments that the Oklahoma National Guard Created a William C. Mitchell Jr. Award for excellence in personnel administration.