Japan interested in submarine designs of German shipbuilding engineer Oswald Flamm according to the Dutch magazine Marineblad dated 1925 No. 2

An item referring to the German magazine Schiffbau dated 19 November 1924 reported that Japan was interessed in three types of submarines of which one of the Flamm type with a displacement of 3,000-7,500 tons. Ocean going and protected against gunfire, aircaft bombs and submerged weapons. To be armed with at least 2-20cm guns, to carry 40 torpedoes with her and with a range of around 25,000 nautical miles. The living accommodation on board allowed a stay of several months at sea. The submarines were such to be constructed that a large diving depth would become possible. This magazine wrote that Japan received drawings from Flamm for a 7,000 tons armoured submarine armed with 2-20cm guns. However the editors doubted if Japan would spend such high building costs for a experimental submarine. On the other hand were rumors that Japan was building of one or more submarines of 3,000 tons displacement conform Flamms’ stability principles make it possible to mount heavy weights on deck without disturbing the stability while submerged.