Tanaka was promoted to major general at the end of 1937, and briefly assigned as Chief of Staff of the Taiwan Army in 1938. However, with the increase in military activity in China due to the Second Sino-Japanese War, Tanaka was quickly reassigned to become chief of staff of the newly-formed Japanese Twenty-First Army from 1938 to 1939. This army was under the control of the China Expeditionary Army would later be assigned the primary role in the Canton Operation (the invasion of Guangdong Province) in southern China; however, Tanaka returned to Japan in August 1939 to serve as Commandant of the Toyama Army Infantry School, before combat operations began.