William S. Key was born on October 6, 1889, in
Dudleyville, Alabama, as the son of Cullen R. and Hadassah Key. Both of his grandfathers had served in the
Confederate Army during the
Civil War. He completed
high school in
Opelika, Alabama and enlisted the
Georgia National Guard as private on April 7, 1907. He was commissioned second lieutenant in summer 1910, but left the National Guard one year later, when his family moved to Oklahoma. Key settled in the town of
Wewoka and established the Key Hardware Co. and the Wewoka Gas Co. and enlisted the
Oklahoma National Guard. He was commissioned again and promoted to first lieutenant on July 12, 1912, and to captain in summer 1916. Key then assumed command of Company G, 1st Oklahoma Infantry Regiment stationed in Wewoka and served on the Mexican Border during the
Pancho Villa Expedition, when his unit was called up for federal service in March 1917 at
Fort Sill,
Oklahoma. Following the
United States' entry into World War I, Key was promoted to the rank of major and embarked for
France. He was attached to the headquarters,
7th Division under Brigadier General
Charles H. Barth and served as divisional quartermaster during
Champagne Defensive,
Château-Thierry,
Saint-Mihiel and the
Meuse–Argonne offensive. While in France, he was promoted to the rank of lieutenant colonel and then to colonel. ==Civil career during interwar period==