Japanese secret submarines: Sen Toku I-400 (war engineering layouts)

Autor: Xavier Pané Seall

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[Aircraft-carrying submarines view] SAKAIDA, Henry; NILA, Gary; TAKAKI, Koji. I-400 Japan’s secret aircraft-carrying strike submarine: Objective Panama Canal. Hikoki, England, 2006. (pg. 100)

In this post I will talk about I-400 submarine, the hit of technical development on japanese navy during Second World War. For a while it was the biggest submarine over the world. I-400 belonged to I class the biggest class of japanese navy. His most important characteristics, highlight an hangar on deck, catapult had about fifty meters long, for throw aircraft, moreover it had incredibly autonomy, approximately 74000 km. Since twenties, Japanese navy classified submarines in three classes: Type I belonged at first kind, these submarines had more one thousand tons. Type II between five hundred and one thousand tons, and finally Type III less than five hundred tons. Submarines class I-400 had a unique design at difference with the other submarines that had stretched and had a narrow design. The I-400 and his equals should have a different design. In the lower part the hull was more spread the double that in the upper side because of the counterbalance weight of the hangar.

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SAKAIDA, Henry; NILA, Gary; TAKAKI, Koji. I-400 Japan’s secret aircraft-carrying strike submarine: Objective Panama Canal. Hikoki, England, 2006. (pg. 138)

Since forties Japanese had produced some air carrier submarines that had a hangar for transporting aircraft inside, such as subclass type AM. It’s mission was especially to carry a reconnaissance plane. Imperial navy, wanted to go beyond with development submarines I-400 class navy, they wanted to utilize these machines for transporting bomber aircraft close to their enemy shores, with the only purpose of bombing their key points. Appearing unexpectedly without being detected and disappearing quickly. It was with the development of the I class that Japanese appeared with an unknown weapon that was produced completely in high secret. They had an important factor in the war, surprise. 

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[Catapult view] SAKAIDA, Heny; NILA, Gary; TAKAKI, Koji. I-400 Japan’s secret aircraft-carrying strike submarine: Objective Panama Canal. Hikoki, England, 2006. (pg. 101)
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[Floats hangar] SAKAIDA, Henry; NILA, Gary; TAKAKI, Koji. I-400 Japan’s secret aicraft-carrying strike submarine: Objective Panama Canal. Hikoki, England, 2006. (pg. 88)

After Japan’s attack on Pearl Harbour, the development of super-sized I-400 class submarine had begin under the commandment Admiral Yamamoto. On march 1942, submarine construction project had completed. Almost a year later, 18 January 1943 the production of first submarine class I started, the I-400 in Kure yard. In these yards also the I-401 was built. Mean While the I-402, the last mega submarines was being built in Sasebo yards. It was only December of 1944 that I-400 was ending it’s construction, a few months before, I-401 and I-402 were completed. At the end of war, the total number of units were three.

These submarines were huge machines that sailed the depths all over the world, with frightening arm potential. The development of these submarines meant more troubles and complications for engineers that worked in it. Not only for it’s dimensions but also because of one more relevant characteristic, the fact that the design included a watertight hangar to store aircraft, meant an important element that should be handled with safety and solid as possible. The aircraft had folding wings operated with a hydraulic system that enabled folding and attaching the wings along the fuselage, in order to store them into the hangar. Also these submarines had a modern system of direct injection of preheat oil that pumped inside the aircraft engines. This allowed to increase on the speed of the building process. This factor enabled the submarines to submerge rapidly so they could disappear from radars. Once the aircraft had completed its rushed, leaving the submarine afloat with a hydraulic crane and large reloaded aircraft inside the hangar.

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[Hangar view] SAKAIDA, Henry; NILA, Gary; TAKAKI, Koji. I-400 Japan’s secret aircrft-carrying strike submarine: Objective Panama Canal. Hikoki, England, 2006. (pg. 80)
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[Hangar view] SAKAIDA, Henry; NILA, Gary; TAKAKI, Koji. I-400 Japan’s secret aircraft-carrying strike submarine: Objective Panama Canal. Hikoki, England, 2006. (pg.81)

 MISSIONS AND TARGETS

Japanese copied German U-boats tactical, these arrived in front of New York coast without being found. With this precedent Japanese navy planned some tactics to attack main cities along west American coast, as San Francisco, Los Angeles, San Diego but also New York and Washington D.C., Miami, those in east coast, with biological weapons to infected Americans citizens. This plan finally was suspended and the target changed.

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Map: Project attack main american cities

Japanese also prepared to attack the Panama Canal, because it had strategic importance. With these attacks, imperial navy could obstruct the pas for allied frigates, increasing the distance that they had to travel to arrive on the Pacific Ocean; in consequence the Japanese gained time. For these mission Japanese navy organized an especial navy air group, the 631 Kokutai. But this plan had to be cancelled because on April 1945 American army began Okinawa Battle, at that moment Japanese needed all it’s arsenal. Their objective was to attac naval Ulithi base for weakening American air carriers structure. This operation began at the end of June of 1945 and the mega submarines I-400 and -401 participated, combined with air carrier submarines AM class, I-13 and I-14. For these mission they organized an especial air attack, the Kogeki Tai (Divine Dragon Especial Group). Pilots that were part of this group were kamikaze. Aircrafts were painted with the colours that america used so that they could plan attacks without being detected, also pilots scheduled to flew very low to remain undetected. Setbacks throughout mission preparation couldn’t carry out attack. Finally War ended before Japanese expected. With the emperor surrender, this frightening weapon didn’t put on service. 

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Map: Project mission  Panama Canal
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Map: Project attack Ulithi Base

 AIRCRAFT SELECTED WITH TRANSPORT IN I-400

These submarines were equipped with Aichi M6A1 “Seiran” aircraft. These aircrafts were produced exclusively for this project. Seirans were two–seater light bomber (pilot and gunner armed with machine gunner), handful. It’s equipped with floats for it could moor on the water. Then aircrafts were loaded with the aid of hydraulic crank, inside the submarine hangar. These airplanes were designed with mechanisms that facilitated aircraft operability and ensured an easy and rapidly assembly. This machines could carry one bomb that weight 800 kg. The head designer was Tashio Ozaki, in tandem with other engineers: Monsishiga Mori, Yasushiro Ozawa, Tomio Koike.

The total production was twenty eight units: one on 1943, ten in 1944 and seventeen in 1945. The development of M6A1 Seiran was executed in complete secrecy.

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[Aichi M6A1 “Seiran”]  La Aviación Japonesa en la Segunda Guerra Mundial (pg. 152)

 TRAINING

During months Seiran pilots, selected for strategic and confidential missions, were training different type of exercises (take off from catapult, moors, bombing simulations. Throughout the months of training the crew recruited for training had to move to antother bases several times because of the allied attacks. Allied were very close to Japanese archipelago.

THE END OF ITS MEGASUBMARINES

With the surrounded of the Japanese empire, the crew of these submarines clear up all the information possible before they were captured by the allied. Japanese submerged the Seiran aircraft in Pacific waters. These stunning landmarks of engineering still had something to do, served as prelude for nuclear submarines development. With the information that Americans had extracted, they were dominating the front soviet in submarine development. For those, who didn’t discover these machines, Americans had to submerge the submarines. 

 

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[Power plant view] SAKAIDA, Herny; NILA, Gary; TAKAKI, Koji. I-400 Japan’s secret aircraft-carrying strike submarine. Objective Panama Canal. Hikoki, England, 2006 (pg. 118)
I-400 Submarine Technical Data
Displacement 3,530 tons (surfaced)

5,223 tons (submerged)

Length 122 meters (400 ft)
Beam 12 meters (39.3 ft)
Draft 7 meters (22.9 ft)
Power plant: 4 x diesel engines

2 x electric motors

Generators 2 x aurxiliary disesel
Speed 18, 7 knots (34,63 km/h) (surfaced)

6,5 knots (12 km/h) (submerged)

Maximum range 37, 500 nautical miles (surfaced)
Test depth: 100 meters (330 ft)
Complement: 21 officers,170 enlisted men
Armament: 1x14cm (140mm or 5.5 inch gun)

Type 11 rear deck gun

10 x 25 mm Type 96 anti-aircraft guns

Torpedo tubes: 8x533mm bow only
Torpedo inventory: 20x type 95
Aircraft: 3 Seiran M6A1

SAKAIDA, Henry; NILA, Gary; TAKAKI, Koji. I-400 Japan’s secret aircraft-carrying strike submarine: Objective Panama Canal. Hikoki, England, 2006. (pg. 16)

 

BIBLIOGRAPHY AND FILMOGRAPHY

-MIKES, Robert C. Japanese Aircraft Code Names & Designations. Schiffer Publishing, EUA, 1993.

-SAKAIDA, Henry; NILA, Gary; TAKAKI, Koji. I-400 Japan’s secret aircraft-carrying strike submarine: Objective Panama Canal. Hikoki, England, 2006.

La Aviación Japonesa en la Segunda Guerra Mundial.

The largest submarine in World War II  (documentary film)

 

 

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