The construction of large oceanic submarines in the Empire of Japan was related to two basic facts. The first was the achievements in the Atlantic and not only by the German submarines during the First World War. The second one, more important, was the concept of "Decisive battle." For over thirty years – after the Battle of Tsushima – the central strategic concept of the Imperial Navy considered the United States of America as the potential enemy. The Washington Treaty, signed by Japan, limited its capabilities of constructing large warships.