Japan’s Underwater Aircraft Carriers – conclusion

American naval personnel inspect the hangar of a Japanese submarine aircraft carrier. The hangar tube was sealed by a two-inch-thick rubber gasket, and the hatch could be opened hydraulically from inside

By early 1945, the Japanese Navy had only 20 modern submarines left, including those in the Sen-toku squadron. Problems arose as the two available I-400 subs began test launching their Sieran planes. Each submarine was required to surface and get its three planes unlimbered and aloft within 30 minutes, but actual training showed that it took some 45 minutes.

Because of an increasing sense of urgency, the Japanese further modified their plans. A torpedo attack was ruled out because the pilots had not yet acquired the requisite skills. It was decided that each of the 10 planes designated for the Panama Canal mission would carry one 1,760-pound bomb, the largest in the Navy’s arsenal and similar to the one that sank the battleship USS Arizona at Pearl Harbor

The departure date was set for mid-June.  The Seiran pilots made practice bombing runs in Nanao Bay against a full-sized replica of the Gatun gates.

The fall of Iwo Jima in March 1945 and the American attack on Okinawa increased the angst among the Japanese planners as the Americans closed in on the home islands. The war had leaped ahead of the planners, and the slated attack on the Panama Canal was canceled. As noted, there were discussions about possibly using the planes in a surprise attack on San Francisco or Los Angles, but those, too, were put aside in favor of a plan to attack enemy carriers at Ulithi, a large staging area near the island of Truk in the Carolines that was used by the Americans.

Mail call on Ulithi, 1945

The two large subs were to proceed toward Ulithi independently for safety and then rendezvous near the target and launch the attack in mid-August. The I-13 never made it to Truk and was correctly presumed lost. The I-14 arrived at Truk on August 4, and its planes flew over Ulithi the following day.

Shortly thereafter word reached the submarines that an atomic bomb had destroyed Hiroshima, and on August 15 the Japanese seamen heard the broadcast from the emperor asking his warriors to lay down their arms. Subsequent orders from the homeland were confusing, with one commanding all submarine captains to execute their predetermined missions. On August 16, the underwater aircraft carriers received explicit orders that their planned attack on Ulithi had been canceled just hours before the I-401 was to launch its planes. The subs were ordered to Kure, and the I-401 turned course toward its fateful encounter with Lt. Cmdr. Johnson and the Segundo.

The Japanese eventually surrendered the I-401 and the other two remaining underwater aircraft carriers. Commander Ariizumi, the developer of the top secret subs, took his own life aboard the I-401 and was quietly buried at sea by the crew. Before encountering the Americans, Nambu had meticulously followed orders from Japan to raise the black flag of surrender and dispose of the vessel’s weapons, including the planes that were catapulted into the sea. Logbooks, code-books, and the like were loaded into weighted sacks and tossed overboard. The torpedoes were jettisoned, with one causing alarm as it circled back toward the large submarine before disappearing harmlessly into the depths.

The Japanese aircraft carrier submarines I-14, I-400, and I-401 are shown in Tokyo Bay at the end of the war. The submarines were destined to be sunk in Hawaiian waters during U.S. Navy torpedo tests.

The three submarines drew considerable attention when they made it back to Tokyo Bay.  Many Americans initially believed the large hangars atop the subs had been designed to haul supplies to troops on distant islands despite the clearly observed catapults. The Americans did receive some assistance from the Japanese crews as they tried to comprehend the purpose of the extraordinary submarines, and by the end of September the Americans had taken the submarines out for cruises. However, none was taken underwater.

The submarines were then taken to Hawaii for further study. The U.S. Navy gleaned what it could from them, and then all three were deliberately sunk by early June 1946 to keep them away from the prying eyes of the inquisitive Soviets.

One of the Seirans did make it to the United States after the war and was eventually restored at an estimated cost of $1 million. It is now on display at the Smithsonian Air and Space Museum. Although the U.S. Navy was somewhat dismissive of the massive submarines, it did take a keen interest in the sound-protective coatings used on the vessels.

There is little doubt that the I-400s were the strategic predecessors to today’s ballistic submarines, especially to the Regulus missile program begun about a decade after World War II that carried nuclear warheads inside waterproof deck hangars. In short, Yamamoto’s plan lived on with “new and improved” versions that helped the United States win the Cold War.

This has been condensed from: Phil Zimmer is a former newspaper reporter and a U.S. Army veteran. He writes on World War II topics from Jamestown, New York.

The wreck of IJN !-401 was located in March 2005.

Click on images to enlarge.

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Military Humor –

 

 

 

 

 

 

 

 

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Farewell Salutes – 

Ronald D. Brown – Pembroke, KY; US Army, Korea, 187th RCT

They stand on the line for us.

Richard E. Cole -(103) – Comfort, TX; US Army Air Corps, WWII, Doolittle’s co-pilot, Lt. Colonel (Ret. 26 y.)

Robert Hendriks – Locust Valley, NY; USMC, Afghanistan, Cpl., 25th Marine Reg./4th Marine Division, KIA

Benjamin Hines – York, PA; USMC, Afghanistan, Sgt., 25th Marine Reg./4th Marine Division, KIA

Delmar Jones – Sesser, IL; US Army, WWII

Venizelos Lagos – Culpepper, VA; US Coast Guard, WWII

Virgil Patterson – FL; US Navy, WWII, PTO

Christopher Slutman – Newark, DE; USMC, Afghanistan, SSgt., 25th Marine Reg./4th Marine Division, KIA

Ly Tong – VIET; South Vietnam Air Force, Black Eagle Fighter Squadron, pilot, POW

Bryan Whitmer – Grand Rapids, OH; US Army Air Corps, WWII, PTO, HQS/457 Artillery/11th Airborne Division

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About GP Cox

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

Posted on April 11, 2019, in Uncategorized, WWII and tagged , , , , , , , , , , . Bookmark the permalink. 107 Comments.

  1. Pleased I read the follow up mate, was intrigued as to the the end result of the Submarines, so there is only one survivor in America, pity really as they do demonstrate a great ability of mankind albeit for destructive purposes.
    Cheers.

    Liked by 1 person

  2. A large fleet of those subs would have been quite a problem had they been available straight after Pearl Harbor I would think.
    Great fascinating post GP something new Well Done!

    Liked by 1 person

  3. Maureen Jenner

    Your recycling of long-forgotten facts prove that they are indeed stranger than fiction. Thank you for such interesting historical nuggets made very much more digestible.

    Liked by 2 people

  4. Certainly glad they were unable to carry out their objectives of Bombing West Coast cities or the Panama Canal, G. –Curt

    Liked by 1 person

  5. An amazing story and an insight into the complexity of the war that is not common knowledge even today.

    Liked by 2 people

  6. Very informative two-parter, GPCOX!

    Liked by 1 person

  7. Amazing, GP. So much for the myth that the Japanese were not successful with submarine warfare- This shows in one area they were far ahead. I learned so much from this series.

    Liked by 1 person

  8. you write with a nice flow – but I think you know that –
    and this line really stood out:

    Subsequent orders from the homeland were confusing,

    because what if it really got confusing – glad it did not

    Liked by 1 person

  9. Although Japan did a lot of harm to my country during World War II, I still admire the economic and military achievements of the Japanese. Now they do send aid to the Philippines even at present.

    Liked by 1 person

    • Oh, I understand! Even during the war, my father admitted many things about the Japanese deserved respect and admiration. Please don’t get me wrong – this blog is not to disparage the Japanese. I am simply rehashing many of the events and trying to keep them in chronological order.

      Like

  10. A fascinating insight into Japanese technology. The potential is great, but I do feel somehow that the numbers required to do any serious damage would have to be so high as to make it ‘uneconomical’ to produce. Incredible nonetheless.

    Liked by 1 person

  11. Interesting way to keep the technology from other countries, but still use it to our benefit. Perhaps we are lucky the war ended when it did.

    Liked by 1 person

  12. It really is fascinating to connect all the dots, and to see precursors of today’s technology in decades-old fleets. On the other hand, it’s equally fascinating to think that all of this was taking place only seventy years ago, give or take, and what seems clunky or badly designed to us now really was cutting edge at the time.

    Liked by 1 person

  13. This is an amazing piece of history about which I knew nothing. Thanks so much for your research, GP, and sharing this with us.

    Liked by 1 person

  14. Great post! The cliffhanger ending of part one was perfect and raised the tension well.
    I like the Farewell Salute to the South Vietnamese pilot. That was a nice touch as was the salute to the Marines lost in Afghanistan.

    Liked by 1 person

  15. Wow. What a fascinating story.

    Liked by 1 person

    • I’m very happy you found it interesting.
      [ May I ask you a personal question? What is your opinion of the National Women’s Hall of Fame planning on inducting “Hanoi” Jane Fonda? ]

      Liked by 1 person

      • (Uf. I had to look it up, as I usually try to avoid the celebrity drama. I can see why veteran members of the town who support it are upset- of course, as a private institution the Hall gets to make the call on whom they deem worthy to make the cut. Of course THEN individuals get to make the call on whether they think the choices are in good taste and whether they’ll financially support and/or visit the Hall. )

        Like

      • (and no, I’m not planning a trip there…)

        Liked by 1 person

  16. Great conclusion, GP. Amazing story

    Liked by 1 person

  17. This was a fascinating mini-series. Those subs certainly could have changed the nature of the war, had they been deployed earlier.

    I saw this post yesterday. I don’t know if you follow the the Imperial War Museum’s twitter feed, but I thought of you when I saw this link to 25 photos from the Korean War. https://www.iwm.org.uk/history/25-photographs-of-the-korean-war

    Liked by 2 people

  18. I saw that plane at the Air Space Museum. I guess I should have read the plaque. Didn’t they recently find one of them off the coast of Hawaii where the Navy had sunk it. I seem to recall reading something about it?

    Liked by 1 person

  19. “all three were deliberately sunk.” Wow! That was an interesting aspect of WWII I had never heard before. Thanks, GP.

    Liked by 1 person

  20. A fascinating bit of history, glad they saved one for posterity.

    Liked by 1 person

  21. Great end to the story. What a clever ship.

    Liked by 1 person

  22. Great story! Thanks.

    Liked by 1 person

  23. Excellent two-part story. Thanks for passing it along!

    Liked by 1 person

  24. I never knew they were that close to attacking us here

    Liked by 1 person

  25. The ingenuity and inventiveness, including the spur-of-the-moment makeshift stuff the soldiers come up with on the spot, are always amazing. We just need to devote this kind of drive and inventiveness to peacetime projects. This was a very interesting story!

    Liked by 1 person

  26. An article I wrote about the same subject from near where I grew up… https://eaglecanyonflyer.wordpress.com/2010/12/10/bombs-over-brookings/

    Liked by 1 person

  27. Glad to know they followed the order to scrap their mission. I could not imagine the damage it would create if the Japanese had these submarines early on. I’m reading In Harm’s Way and it’s heartbreaking to read about the lives lost after it was torpedoed by an I-58 sub.

    Liked by 1 person

  28. Thanks for the interesting conclusion, GP!

    Liked by 1 person

  29. Amazing story! And, with all the reading I’ve done on WWII, I do not remember ever encountered anything about these underwater subs! But, then again, a lot of my focus has been on the war in Europe. Thanks for sharing GP!

    Liked by 1 person

    • I understand. There is so much information on each theater of operation, it is too difficult to learn everything about the entire war (at least for me!) 🙂

      Like

  30. Great posts, GP! The I-400s are a fascinating subject.

    There is a little known detail concerning the I-400 and I-401 mission to bomb American carriers at Ulithi Atoll when the war ended. Their six Seirans were painted in Aluminum dope and given American markings before the submarines left Japan. The crews were not happy about the change in markings, but the insignia would help achieve surprise if the aircraft were detected. The attack on the fleet anchorage at Ulithi was scheduled for 17 August 1945. Fortunately the war ended on 15 August and both submarines received new orders. After some discussion, it was decided to jettison the Seirans in their American markings and return to Japan. It was not until 1982 that the repainting of the Seirans was first revealed. The attack was to have been a Kamikaze mission so the Seirans were to have been assembled without floats. In addition, the cap on the vertical stabilizer was left off.

    I built a model of a Seiran in American markings here: https://inchhighguy.wordpress.com/2019/02/14/tamiya-1-72-aichi-a6m-seiran-nanzan/

    Liked by 2 people

  31. Ulithi had recently been captured when the USS Hancock (Uncle Donald W. Wilson on the crew) was part of the fleet that staged there from October 1944 on through the end of the war. Japan even sent kiaten suicide submarines there.

    Liked by 2 people

  32. There is somewhat of a parallel between these Japanese submarines and the German’s jet aircraft, regarding technological advancements.

    Liked by 2 people

  33. Interesting post, GP…thank you. My thoughts and prayers are with the families of the three U.S. Marines who were killed earlier this week…so young.

    Liked by 1 person

  34. That’s a nice conclusion, GP. Just as well they didn’t have those much earlier in the war.
    Best wishes, Pete.

    Liked by 1 person

  1. Pingback: Featured Blogger Report: Japan’s Underwater Aircraft Carriers – conclusion by PacificParatro oper #AceHistoryDesk reports | ' Ace Worldwide History '

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