Kaiyō Maru was a steam-powered warship imported by the late Tokugawa shogunate and built in the Netherlands. As the most advanced warship of the Japanese navy at that time, it symbolized the shogunate's determination to pursue modernization. In 1868, during the Boshin War, the vessel ran aground and sank off Hakodate amid a severe storm. Its remaining wreckage is designated as a national historic site of Japan, bearing witness to the turbulent era and the revolutionary progress of naval technology.