In 1938, a year after the Marco Polo Bridge Incident, Okamura was assigned as the commander in chief of the Japanese Eleventh Army, which participated in numerous major engagements in the Second Sino-Japanese War, notably the Battles of Wuhan, Nanchang and Changsha. According to historians Yoshiaki Yoshimi and Seiya Matsuno, Okamura was authorized by Emperor Hirohito to use chemical weapons during those battles.