Japan’s Panama Canal Buster
By John Geoghegan; research assistance by Takuji Ozasayama

Aviation History  | 0 comments  |  Print This Post  |  Email This Post

One of the key requirements of the Seiran was that it could be rolled out on a dolly, assembled by its ground crew and launched in a very short time. Reports vary on how fast this could be accomplished. According to Commander Nambu, intensive training enabled the I-401 crew to launch three planes within 45 minutes. But Nambu also noted that given the rough handling the Seirans received during sea launches and landings, it was difficult to keep all three in good operating condition at the same time.

The Smithsonian notes the Seirans had “interesting design features built in…that ranged in engineering quality from the ingenious to the seemingly absurd.” The fact that some of the floatplane’s parts were painted with luminescent paint for night assembly certainly has to fall into the former category. Lieutenant Asamura claimed the Seiran cost “50 times more than a Zero to produce,” and though it’s not possible to confirm the exact cost, clearly they were expensive to manufacture.

Although some German and British subs had carried reconnaissance aircraft on their decks during World War I, Japan was the only nation to use submarine-launched aircraft in WWII. At the beginning of the war, it had approximately 63 oceangoing subs, 11 carrying one catapult-launched reconnaissance plane each. Even­tually, Japan would expand this to a total of 41 aircraft-carrying subs.

Admiral Isoroku Yamamoto, commander in chief of the Combined Fleet and architect of the Pearl Harbor attack, gets credit for the I-400 class of submarines and its Seiran bomber, though I-401’s Commander Na­mbu says the actual idea for an underwater aircraft carrier probably originated from lower down in the command structure. Admiral Yamamoto’s vision in 1942 was for the underwater aircraft carriers to launch their Seiran attack bombers against U.S. coastal cities such as Washington, New York, San Francisco and Los Angeles, to deliver a Doolittle-like blow to American morale.

The original plan was to build 18 I-400– class subs, but after Yamamoto was ambushed and killed by Lockheed P-38 Lightnings in April 1943, the guiding hand behind the I-400 subs was gone. Construction plans were scaled back to nine subs, due in part to steel shortages. Actual construction began on five subs but was later reduced to three, of which only two (I-400 and I-401) made it into service. A third, I-402, was converted into a fuel tanker and completed in July 1945 but never saw active duty.

Final design plans for the underwater aircraft carriers were finished by May 1942, and construction on the first sub (I-400) began at Kure’s dockyards in January 1943. I-401’s construction quickly followed. By December 30, 1944, I-400 was complete, and I-401 was completed less than two weeks later. Both subs immediately deployed for their shakedown cruises.

In December 1944, the Imperial Japanese Navy organized the 1st Submarine Flotilla and 631st Kokutai (Air Corps), with Captain Tatsunoke Ariizumi commanding both units. The force consisted of I-400, I-401 and two AM-class subs, I-13 and I-14, which were smaller and carried two Seirans each, for a total of 10 Seiran bombers. An experienced naval officer from a distinguished military family, Ariizumi and had been in charge of the midget sub attacks at Pearl Harbor.

In March 1945, Vice Adm. Jisaburo Ozawa, vice chief of the navy general staff, toyed with a plan to use the Seirans to unleash biological weapons on a U.S. West Coast city in revenge for the firebombing of Tokyo. The notorious Japanese Unit 731 had already conducted successful experiments in Manchuria using rats infected with bubonic plague and other diseases to kill Chinese citizens. But the opera­tion was canceled later that month by General Yoshijiro Umezu, chief of the army general staff, who declared, “Germ warfare against the United States would escalate to war against all humanity.” Instead, the Japanese decided to target the Panama Canal.

Tags: Aviation History, Flight Technology, Military Technology, Sea-Air Operations, World War II

You can follow any responses to this entry through the RSS 2.0 feed. You can leave a comment, or trackback from your own site.