He was promoted to lieutenant general in October 1898 and was placed in command of the newly-formed IJA 8th Division. The infamous Hakkōda Mountains incident in which 199 of 210 members of its 5th Infantry Regiment froze to death in Hakkōda Mountains during training exercise occurred during his command. Tatsumi subsequently led the division into combat during the Russo-Japanese War. Two of the principal battles of his military career were at Sandepu and Mukden in 1905. He was promoted to full general in May 1906, but retired two months later and died the following March.