Soejima Jiro went to Manchuria (1915), and attempted unsuccessfully to join a Mongolian volunteer army and roamed over Manchuria. Arriving in Mukden (1918) he engaged in an investigation of Manchurian industry. Later joined the army of Grigori Mihailovitch Semionov, a White Russian general. When Japanese troops were sent to Siberia (1918), he engaged in the transportation of war materiels for the Japanese Army.
Then he wandered again over the Chinese continent. Became a reporter for the Tientsin Nichinichi Shimbun (newspaper) (1922) and then the Kyokuto Shuho (Far Eastern Weekly) in Dairen. Explored Central Asian areas including Turkey for two years, covering 5,000 miles.