Komatsubara was an assistant military attaché in Russia between 1919 and 1925, then military attaché there from 1927 to 1929. Promoted to colonel in 1929, he commanded a regiment. In April 1932, he became director of the Harbin Special Service Agency in northern Manchuria, with the task of collecting and analyzing intelligence concerning Soviet activities. Made a major general in 1934, he commanded infantry brigades. In March 1937, he was promoted to lieutenant general and given command of Second Independent Garrison in Manchuria, and in July 1938, he took command of the 23rd Division in Manchuria.
While Komatsubara was commanding the 23rd Division, a clash occurred between Japanese and Soviet forces in the border area between Manzhoudiguo (Manchoutikuo) and Mongolia. In initiating the fighting, the Japanese Guandong (Kwantung) Army underestimated Soviet strength and disregarded instructions from Tokyo. Komatsubara himself did not accurately estimate the Soviet forces led by Soviet Lieutenant General Georgii Zhukov. His own division was newly organized, and though mobile, it was only lightly armed. Komatsubara began the May to September 1939 Battle of Nomonhan (Khalkhin-Gol), and his division was annihilated by Soviet tanks and artillery: of some 15,975 men in the 23rd Division, 11,230 were casualties during the battle. Komatsubara was made the scapegoat for the Japanese defeat. Removed from command, he retired from the service in 1940. He died within the year, on 6 October 1940. Tobe Ryoici
Coox, Alvin. D. Nomonhan: Japan against Russia, 1939. 2 vols. Stanford, CA: Stanford University Press, 1985.