Kaiyō No.1-class oceanographic research ship

The Kaiyō No. 1 class was a class of oceanographic research and weather ships of the Imperial Japanese Navy, officially designated the 200-ton oceanographic research ship, that served during World War II. In 1938 the navy wanted to investigate the weather and ocean currents of a potential future battlefield and had the ships built for that purpose, taking the Hokkaido Fisheries Research Institute vessel San’yō Maru as the sample for the first ship. All of the sister ships were built by Mitsubishi Heavy Industries at its Shimonoseki shipyard. They were assigned to the Hydrographic Department and controlled directly by the Naval Ministry, so as government ships they flew the civil ensign rather than the naval ensign, and their crews were civil servants apart from several warrant officers.