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-124
The submarine was the fourth Japanese submarine lost in action in World War II. It has been surrounded in controversy since it was lost. In World War II there were claims that two submarines had been lost in the attack on Darwin; that its crew remained alive for some time; and that divers heard crew movement inside the hull. Later it was reported by both Japanese and American sources that "the "I 124" with her Division Commander Keiyu Endo, embarked, sank with all those on board in water only forty feet deep. US Navy divers were sent down and entered the submarine, and removed naval code books, a godsend for the Navy codebreakers at Pearl Harbor". However, this was later disproved by historian Dr Tom Lewis, in his book "Sensuikan I-124"; later re-published as "Darwin's Submarine I-124".