 After serving in a staff position within the personnel department of the Imperial Japanese Army General Staff, Sakai was dispatched to France as a military attaché from 1915–1917, and was thus able to observe the fighting in World War I firsthand as an official observer from the Japanese government.On his return to Japan, Sakai was again assigned to staff positions, but due to his fluency in French and European experience, was selected to participate in the Japanese delegation to the Versailles Peace Treaty negotiations.His rise through the ranks was steady and rapid thereafter