A graduate of the United States Military Academy, Devers was commissioned in the field artillery in 1909. During World War I, he was an instructor at the School of Fire at Fort Sill, Oklahoma, and did not serve in France until after the November 11 armistice ended the fighting, when he attended the French artillery school at Treves. Between the two world wars he was a staunch advocate of mechanization at a time when the idea of phasing out horses met strong resistance from conservative gunners.