Japan’s Underwater Aircraft Carrier I-400 series conclusion

Watch the surrender of a I-400 class Supersubmarine.

Admiral Isoroku Yamamoto called for the construction of 18 of the massive submarines carrying a total of 36 attack planes. The name of the special submarine class was abbreviated to Sen-toku.

The attack planes had to be designed from scratch. The need for speed, range and a decent sized bomb payload required tradeoffs. The wings had to be foldable to fit inside the tube, or hangar, atop the submarine. The design work, testing, and building of the plane was outsourced to the Aichi Aircraft Company.

The I-400 program did have its detractors in the heavily bureaucratic Imperial Japanese Navy.  After the defeat at Midway in early June 1942, Japan became more focused on defending the homeland and far less on possible attacks on the U.S. mainland using the large submarines. The death of Yamamoto in mid-April 1943, played further into the hands of conservative Japanese commanders. Cutbacks were ordered in the number of submarines to be built.  .

The first test flight of the Aichi attack plane occurred on November 8, 1943. The plane, called Seiran or “storm from a clear sky,” reportedly handled fairly well as the world’s first sub-borne attack bomber. The Japanese began compiling limited available information on the heavily fortified Panama Canal. Their analysis showed that destroying the gate opening onto Gatun Lake would create a massive outpouring of water, destroying the other gates in its path while rushing toward the Caribbean Sea.

After weeks of planning, the Japanese came up with a strategy to attack the Gatun locks at dawn when the gates were closed and presumably the defenses were lax. The planners had nearly a full year to formulate the attack for early 1945. But there were problems ahead because none of the submarines were complete and the planes were not yet in the production stage.

The Japanese labored on, and by the end of 1944 the I-400 and the smaller I-13 were completed and turned over to the Navy. In early January 1945, the I-401 was commissioned  and the I-14, the last of the underwater aircraft carriers, was put into service by mid-March 1945.

As an important aside, it should be noted that while preparations for the attack on the Panama Canal went forward, Vice Admiral Jisaburo Ozawa, vice-chief of the Naval General Staff, floated another idea for the use of the Sen-toku submarines. He suggested arming the Seiran planes with biological weapons to be unleashed against a populated area on the West Coast of the United States.

Dr. Shiro Ishii, Japan’s top virus expert and head of the Army’s notorious 731 unit in Manchuria, was consulted. He recommended that the planes drop plague-inflected fleas, something he had tested with success in China.  On the United States with San Francisco, Los Angeles, or San Diego he suggested as targets. The plan was discarded in late March by the head of the Army’s general staff who called it  “unpardonable on humanitarian grounds.”

In effect, the Japanese Army, which had led the development of biological weapons and had tested them on Chinese and American captives, nixed the idea of using the weapons late in the war on American civilians, perhaps in the belief that the war was already lost.

I-400 class submarine located off Oahu.

The subs were later scuttled.

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Upcoming –   For those in the U.S. and around the world, reading here – Happy Thanksgiving!! 2022

Thanksgiving from: Pacific Paratrooper | Pacific Paratrooper (wordpress.com)

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Military Humor – 

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Farewell Salutes – 

Walter Alesi – Salem, OH; USMC, WWII,PTO, 5/4th Marines

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Take a moment to honor them.

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Benge Elliot – Lamesa, TX; US Army, medical

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Willis Holton – Jacksonville, FL; US Air Force, Korea

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James Rotunno – Brooklyn, NY; US Army, WWII, ETO, SSgt. # 32204944, Co K/3/157/ 45th Infantry Division, KIA (Reipertswiller, FRA)

Robert A. Wright – Whitesville, KY; US Army, Korea, Pfc. # 15381551, Co C/1/19/24th Infantry Division, KIA (Taejon, SK)

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About GP

Everett Smith served with the Headquarters Company, 187th Regiment, 11th A/B Division during WWII. This site is in tribute to my father, "Smitty." GP is a member of the 11th Airborne Association. Member # 4511 and extremely proud of that fact!

Posted on November 21, 2022, in Current News, Post WWII, WWII and tagged , , , , , , , , , , . Bookmark the permalink. 138 Comments.

  1. Very interesting what they had invented to win the war. xx Michael

    Liked by 1 person

  2. The two videos are truly dramatic — marvelous research for these submarine articles.

    Liked by 1 person

  3. Info I did not know about ->Dr. Shiro Ishii, Japan’s top virus expert wanted to drop infected fleas from the sky. <- It reminds me about the mustard gas used in WW1. The tip of the iceberg as the saying goes. Oh boy!? A crazy, mixed up world.😥

    Like

  4. Truly amazing! Thanks for sharing important information about our past. I am hoping that all is well in your world and that you just had a wonderful Thanksgiving celebration with those you care about. May your week ahead be blessed with love and light!

    Liked by 1 person

    • What a wonderful comment, Lorrie. Yes, all is well here and I thoroughly enjoyed my turkey! Thank you for asking. I hope your world is giving you all that you dream of.

      Like

      • I was a very lucky girl, to have been invited to two different Thanksgiving celebrations…one on Thursday…and one yesterday! And they were both incredibly wonderful…sharing time with really nice, cool people!! Thank you!
        And yes…I am busy exploring all wonderful things!! 🙂

        Liked by 1 person

  5. First I’ve ever heard of these unique ships, GP. Fascinating!

    Liked by 1 person

  6. Happy Thanksgiving, GP

    Liked by 1 person

  7. I imagine one of the subs was kept by the Americans for engineering studies? I had not heard of plan of the plague infested fleas being released, and that it had been tested in China.

    On a cheerier note, Happy Thanksgiving, GP! Michael’s tree is doing well going into the winter. I will have to measure the height, but I think it is at least 10 feet tall now. I remember raising that line of trees from when they were only a few inches tall!

    Liked by 1 person

    • The supersub was quite a piece of machinery that I’m sure they studied before sinking them.

      I am so thrilled Michael’s tree is doing well! I have all the pictures in a frame, with the dates and of course its first pine cones! I think I’ve told everyone I know of what you’ve done!!

      Liked by 1 person

  8. This is a wonderful write.

    Liked by 1 person

  9. “[U]npardonable on humanitarian grounds,” was the ’45 Japanese Army way of saying “Consider the downside of offending people who are about to kick our butt.”

    Liked by 1 person

  10. Happy Thanksgiving to you and your family! 🙂 (((HUGS))) ❤️🙏❤️

    Liked by 1 person

  11. Had the Japanese bombed the locks at the Panama Canal or dropped biological weapons off the coast of California…. a terrifying ‘what if’.

    Liked by 2 people

  12. Scary thoughts about the plague to be released on the West Coast. That could wipe out the whole West Coast population and then some! Glad humanitarian sentiment prevailed. Happy Thanksgiving, GP.

    Liked by 2 people

  13. Great story, thanks.

    Liked by 1 person

  14. Reblogged this on History and Hobbies and commented:
    Part two of an interesting true WW2 story.

    Liked by 2 people

  15. Happy Thanksgiving to you and the visitors of this blog

    Liked by 2 people

  16. Thank you for completing this story

    Liked by 2 people

  17. Was surprised that the Japanese had planned to attack the Panama Canal first of all. Then found it amazing that they decided not to use biological weapons against the US. Wish our government felt that way today.

    Liked by 2 people

  18. Super post, GP. Thank you.

    Liked by 2 people

  19. I didn’t know that the Japanese had considered using biological weapons.

    Liked by 2 people

  20. What a concept! Wedding those planes to the submarine. Thanks for this history lesson, GP.

    Liked by 2 people

  21. Thanks for the amazing color videos. Seeing the surrender of this sub conveys the size and capabilities of these unique warships. It was fascinating to see the interaction between the Japanese and U.S. crews. There didn’t appear to be any animosity or hostility. Not surprisingly perhaps, it seemed that both sides were thankful that they weren’t killing or being killed.

    Liked by 2 people

  22. What!? Releasing the plague? I guess all possibilities are on the table –

    Liked by 2 people

  23. Very interesting. I never heard anything about this before . Thanks , GP.

    Liked by 3 people

  24. The video shows just how impressively large that sub was. And the consideration of plague-fleas being launched against the US cicilian population also shows how evil some of the Japanese were.
    Best wishes, Pete.

    Liked by 3 people

  25. Amazing to think about the “what-ifs” in history if the war had not played out as it did. Always like these posts which provide more context as to what took place, as well as what could have taken place. (That turkey pictured above certainly doesn’t look eager to be on anyone’s table…🙂)

    Liked by 3 people

  26. Another example of a great idea coming too late to make any difference!

    Liked by 3 people

    • The idea was early enough, but the manufacture was slow. That’s why I always say that we could not have won if we didn’t have the home front joined together the way they were.

      Liked by 1 person

  27. An excellent conclusion to one of your best ever topics in my opinion. And that was a really big submarine!
    The Head of the Army’s General Staff did say the use of these diseases was ““unpardonable on humanitarian grounds” but he also made the point that, essentially, what goes around comes around. In other words, release some crazed dragon in the USA, and there’s every chance that one day it will be back to eat you.

    Liked by 3 people

  28. Lulu: “Yeah that first Navy Rider cartoon would be our Dada on a boat in the harbor.”
    Charlee: “He even got seasick once in the restaurant at the end of the pier when the waves were hitting it too hard!”

    Liked by 3 people

  29. An interesting story I had never heard of before. Thanks for the on-going education.

    Liked by 3 people

  30. I’ve never read of plans to attack the Panama Canal, but as soon as I came across that in your post, it made perfect sense. Striking at a seemingly “small” target could have caused damage far beyond any imagined even by the Japanese. As for the biological warfare, there are some who believe it’s been carried out relatively recently, by another country. I sure can’t judge that, but if the Chinese had taken some inspiration from the Japanese, it would be quite an irony.

    Liked by 3 people

  31. Quite remarkable. Thank you for sharing this.

    Liked by 3 people

  32. Fascinating article and first rate ‘toons, GP. When my Dad was at the Naval Postgraduate School in Monterey back in the early 60s when World War II vets were getting their Bachelors degree that they were unable to get during the War, he was the only (what became known as) surface warfare officer aboard a ship-based field trip on Monterey Bay with a bunch of airedales. He had his hands in his pockets when the ship hit a rogue wave or a swell. He fell down which the naval aviators thought was hilarious. You Coast Guard cartoon reminded me of that story. Happy Thanksgiving your and the Mrs.

    Liked by 3 people

  33. I didn’t know the Japanese considered biological warfare. Thank G-d, some “humanitarian” heads prevailed!
    Happy Thanksgiving, GP! 🦃

    Liked by 2 people

  34. I am so glad the war ended before these ships could carry out their devastating missions. I doubt either crippling the canal or unleashing a virus on the west coast would have changed the outcome of the war, but it would have lengthened it. Given a longer gap between the end of the war in Europe and the war in the Pacific would have brought the Russians deeper into the Pacific Theater and perhaps the post-war efforts. That could have had a major impact.

    Thanks so much for bringing us this story, GP. I hope you have a wonderful Thanksgiving!

    Liked by 2 people

  35. So what was not only thinkable but done on Chinese civilians and American POWs when the tide was in their favour becomes unthinkable once doubts set in as to victory….some moral stance there!

    Liked by 2 people

  36. Just to let you know…

    The floatplane image is not a Seiran but this one GP.

    https://en.m.wikipedia.org/wiki/Aichi_E13A

    Liked by 2 people

  37. Always enjoy those “Critical Past” video clips, which often are of rarely seen historical moments.

    Liked by 3 people

  38. Amazing technology for its time. I guess the original idea has been brought forward with subs carrying ballistic missiles instead of planes. Interesting article, thanks GP.

    Liked by 4 people

  39. An impressive ship, with a goal that could have been disastrous for the West Coast. And it’s scary that biological warfare was being developed.

    Liked by 4 people

  40. Happy Thanksgiving 🦃 G.P.!

    Liked by 4 people

  41. While viewing the surrender of this impressive submarine, I couldn’t help but think about how timing is crucial to successful outcomes. The development and possible deployment of this type of ship has a strong parallel to Nazi Germany’s development of jet engine powered aircraft. Both nations simply ran out of time to see their projects to successful completion. Thankfully, the world dodged a major bullet regarding this submarine.

    Liked by 7 people

  42. Another fascinating read! Also, I had no idea that releasing the plague was ever considered!

    Liked by 4 people

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  2. Pingback: Japan’s Underwater Aircraft Carrier I-400 series conclusion | Ned Hamson's Second Line View of the News

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