In March 1937 Tanaka was appointed section chief of the Military Affairs Bureau. After two years in Tokyo he became chief of staff of Mongolia Garrison Army.
Promoted to lieutenant general he became chief of the Military Operations Sections. In December 1942 he was sent to reinforce Guadalcanal. Tanaka was able to inflict a heavy defeat on the US Army. After criticizing Hideki Tojo in a conversation with a fellow officer he was demoted and posted to the Southern Army in Saigon.
In March 1943 Tanaka was sent to Burma as commander of 18th Division. Abandoned by General Masaki Honda, Tanaka's men were badly defeated by General Joseph Stilwell and his troops. He was badly wounded in May 1945 but he survived the war. Shinichi Tanaka died in 1969.