The Washington Naval Treaty restrictions did not apply to ships with a displacement of up to 10,000 tons, so Japan started designing small aircraft carriers in addition to large ones. Ryūjō was designed taking the experience of operating Hōshō into account: She received a double-deck hangar, which allowed for increasing the air group size. Ryūjō participated in the Sino-Japanese War from 1937 through 1939. During World War II, the aircraft carrier supported landings in the Philippines, covered convoys headed to the Dutch East Indies, and participated in raids in the Indian Ocean and around the Aleutian Islands.