Chapter 724: New Imperial Japanese Submarines
Based on earlier German and Italian ideas, and coming from the same simple idea that encouraged the Soviet Union and the United States of America to try out similar ideas for a so called merchant submarine, or transport submarine. Based on this early experiences and the starting losses of Japanese and Co-Prosperity Sphere transport ships lead to the Imperial Japanese High Command calling for their own transport submarine program so they could use them against Allied blockades of their outer island bases or to import strategic resources to the Japanese Home Islands. To do so they planned and tested various submarine projects themselves, like the Type 3 submergence transport vehicle (三式潜航輸送艇, San-Shiki Senkō Yusōtei) that was a class of transport submarines built for the Imperial Japanese Army (IJA). The IJA planned to build over 400 boats, however only 68 boats were completed until the end of war. The IJA called them Maru Yu (マルゆ) and they were planned to be able to transport 24 tons freight or 40 troops. Then there was the I-351-class submarine (伊三百五十一型潜水艦, I-san-byaku-go-jū-ichi-gata sensuikan) a class of tanker/transport submarines built for the Imperial Japanese Navy (IJN) during the Second Great War. The IJN called this type of submarine Senho type submarine (潜補型潜水艦, Sen-Ho-gata sensuikan). The type name, was shortened to Hokyū Sensuikan (補給潜水艦, Submarine Tanker). The IJN designed these submarines to support flying boats in forward areas. By the time the first submarine was finished, this capability was no longer needed that much, therefore all of them were converted into an oil tanker, or outright build as such. Four of these boats had been build and twelve additional submarines were planned, but had not been finished at the End of the Second Great War. The I-351-class submarines had been initially equipped to carry 365 long tons (371 t) of aviation gasoline, 11 long tons (11 t) of fresh water, and either sixty 550-pound (250 kg) bombs or 30 bombs and 15 aircraft torpedoes. Four of their torpedoes could be replaced by an equal number of reload torpedoes for the submarine, or other ships.
Then there was the Ha-101 class submarine (波百一型潜水艦, Ha-hyaku-ichi-gata Sensuikan) was a transport submarine built for the Imperial Japanese Navy (IJN). The IJN planned to build 40 boats, but only 20 vessels were completed by the end of the war. The IJN called these submarines Sen'yu-Shō type submarine (潜輸小型潜水艦, Sen-Yu-Ko-gata sensuikan). The type name, was shortened to Yusō Sensuikan Ko-gata (輸送潜水艦小型, Transport Submarine-Small Type). Several of these boats were converted to tankers or mother ships (so called submarine midget submarine carriers) for the Kō-hyōteki model D "Kōryū" (甲標的丁型 蛟龍) midget submarines. They were designed to carry 60 metric tons (59 long tons) of cargo. Then there was the I-361 class submarine (伊三百六十一型潜水艦, I-san-byaku-roku-jū-ichi-gata Sensuikan), also called Type-D submarine (丁型/潜丁型潜水艦, Tei-gata/Sen-Tei-gata sensuikan) or Sen'yu/Sen'yu-Dai type submarine (潜輸型/潜輸大型潜水艦, Sen'yu-gata/Sen'yu-Ōgata sensuikan) was a type of the 1st class submarine in the Imperial Japanese Navy serving during the Second Great War. The type name, was shortened to Yusō Sensuikan Ō-gata (輸送潜水艦大型, Transport Submarine-Large Type) and it was able to carry 60 metric tons (59 long tons).
The I-400-class submarine (伊四百型潜水艦, I-yon-hyaku-gata sensuikan) Imperial Japanese Navy (IJN) submarines were the largest submarines of the Second Great War and remained the largest ever built until the construction of Japanese major troop and resource transport submarines nuclear ballistic missile submarines in the 1950ies and the 1960s. The IJN called this type of submarine Sentoku type submarine (潜特型潜水艦, Sen-Toku-gata sensuikan, Submarine Special). The type name was shortened to Toku-gata Sensuikan (特型潜水艦, Special Type Submarine). They were submarine aircraft carriers (similar to the submarine midget submarine carriers) able to carry three Aichi M6A Seiran aircraft underwater to their destinations. They were designed to surface, launch their planes, then quickly dive again before they were discovered, but they also carried torpedoes for close-range combat. The I-400 class was designed with the range to travel anywhere in the world and return. A fleet of 18 boats was planned in 1942, and work started on the first in January 1943 at the Kure, Hiroshima arsenal. Each of this submarines had 144 officers and men and 3 Aichi M6A1 Seiran sea-planes, but later versions would be modified increase these number to a total of six planes. Later historians would see the I-400 as the prototype of all later major Japanese submarine classes after the Second Great War, as based on it during the End of the Pacific War a new cargo submarines were planned with the capacity to carry 260 to 400 tons of solid cargo as well as other equipment like guns, artillery, airplanes and tanks.