Tanaka was promoted to major general at the end of 1937, and briefly assigned as Chief of Staff of the Taiwan Army in 1938.

[2] 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.

As part of the Japanese 12th Army, the division participated in counter-insurgency operations in northern China as well as the Battle of South Shanxi in May 1941, and the subsequent Hundred Regiments Offensive.

However, he was then turned over to the Kuomintang Nanjing War Crimes Tribunal in connection with the actions of IJA 23rd Army in China.

Tanaka had both permitted and, at times, ordered and encouraged his troops to commit atrocities, including the rape, torture, and massacres of Chinese POWs and civilians.