Submarines of the Imperial Japanese Navy
In 1904 Kawasaki Dockyard Company purchased plans for a modified version directly from Holland, and built two boats (Hulls No. 6 and 7), with the help of two American engineers, Chase and Herbert, who had been assistants to Holland. The Kawasaki-type submarines displaced 63 and 95 tons when submerged, and measured in overall length, respectively. both vessels measured at the beam. This contrasted with the original five imported Hollands-type submarines which had arrived that same year, at over 100 tons submerged, in overall length and beam. The Kawasaki Type #6 and #7 submarines had gained extra speed and reduced fuel consumption by . However both boats could launch only one torpedo, and each was manned by 14 sailors, whereas the imported Holland-type submarines could fire two torpedoes and could be operated by 13 sailors. This new type was designated the Type 6 submarine by the Imperial Japanese Navy, and was used primarily for test purposes.
Japanese submarine I-54 (1926)
The four Kaidai Type 3a vessels were the first mass-produced Japanese fleet submarines. Based largely on the indigenous Kaidai Type II ("I-52") a strengthened double hull, their design was also influenced by the largest of the German submarines in Japanese hands, the SM U-125. The hull had almost the same outer dimensions as the "I-52", but the increased thickness of the inner hull permitted a diving depth of 60 meters. Internal volume was slightly increased by making the hull slightly trapezoidal in cross-section, at the expense of 300 tons of additional displacement. External differences included an anti-submarine net cutter on the bow, as well as an O-ring for towing purposes.