After graduating from the 22nd class of the Army Staff College in 1910, Sugiyama served in Section 2 (Intelligence) within the Imperial Japanese Army General Staff. He was posted as military attaché to the Philippines and Singapore in 1912, disguised as a civilian trading company employee, and disguised as a Imperial Japanese Navy lieutenant, joined in an inspection tour of the United States Navy base at Subic Bay. Promoted to major in 1913, he was posted again as military attaché to British India in 1915, where he met in secret with Indian independence activists Rash Behari Bose and Subhas Chandra Bose. In 1918, he was sent as a military observer to the Middle Eastern theatre of World War I. At the end of the war, he served on the League of Nations committee on military aviation.