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

Norma Bidner (101) – Gibson City, IL; Civilian, WWII, Chanute Air Force Base

Take a moment to honor them.

Robert Black – Boise, ID; US Navy, Chaplain, the Gray Shepard Award, USS Racine

Raymond Cattell (101) – Birmingham, ENG; Royal Navy, WWII, HMS Glasgow & HMS King George V

Benge Elliot – Lamesa, TX; US Army, medical

Levin Ferrin (100) – Phoenix, AZ; US Army Air Corps, WWII, 82nd Airborne Division

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

Francis P. Martin – Scranton, PA; US Army, WWII, ETO, Pfc. # 33457416, Co D/1/157/45th Infantry Division, KIA (Reipertswiller, FRA)

Walter Nies – Eureka, SD; US Army Air Corps, WWII, ETO, SSgt. # 37307545, Tail gunner, 96 BS/2 BG/15th Air Force, POW, KWC (Stalag Luft 6, GER)

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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