ノモンハン事件
In August 1937, Sonobe was assigned command the IJA 7th Division. In February 1938, the division was permanently assigned to Kwantung Army, but arrived too late to participate in the Battle of Lake Khasan in July 1938. Parts of division were reinforcing IJA 23rd division during the disastrous Battles of Khalkhin Gol in 1939. In August 1939, Sonobe was reassigned back to Japan and assigned to command the Central District Army, a reserve force with responsibility for defense of the Japanese home islands.