A Seiran floatplane bombers

A Seiran floatplane bombers

I-400 Class submarine and the technology of terror

Japan, during the Second World War, was quite specialized in terms of what navy technology she advanced

Those readers who follow maritime news will likely have read last month about the rediscovery and identification of a sunken Second World War-era submarine cable repair ship off the coast of Oahu, Hawaii.

The USS Kailua made quite a few headlines when she was found half a 800 metres beneath the surface, resting largely intact despite the fact that she had been deliberately torpedoed and sunk by the American Navy in 1946.

What got less coverage was the fact that in the same immediate vicinity were two sunken Japanese submarines.  One was a mini-sub and the other was one of the most remarkable advances in naval weaponry to come out of the Second World War: an I-400 class submarine.

Japan focused her wartime energies on the Pacific theatre, of course, and therefore was quite specialized in terms of what technology she advanced. Very little was spent on terrestrial combat, but air and naval innovations got a lot of attention.

There were only three I-400 class submarines ever created (I-400, I-401, I-402), and they were absolutely without par at the time.

At 122 metres in length and a surface displacement of 3,530 tons they were the largest submarines on earth until the nuclear ballistic missile subs of the 1960s, and to this day remain the only submarines in history that could carry and launch airplanes.

The I-400 class were known as the Sentoku in Japan (meaning “special submarine”) and were conceived by the same man who designed the attack on Pearl Harbour, Japanese Combined Fleet Commander-in-Chief Admiral Isoroku Yamamoto.

Design and conceptualization of this hybrid weapon began one month after Pearl Harbour, in January 1942.

Construction began in 1943, and originally 18 were commissioned. The subs development was set back with the death of Admiral Yamamoto in April of that year when his plane was shot down over the Solomon Islands by the Americans, and the commission was scaled back to 11, and then to only five by the end of the year.

Only three were completed in 1945, at which point the trajectory of the war had shifted and materials and money were drying up. Japan was losing the conflict.

The concept behind the design was to have a vessel that was not only a submarine, but also an aircraft carrier.

Yamamoto wanted the Sentoku to be capable of terrorizing not just the west coast of North America, but the more heavily populated east coast as well.

In theory, it could emerge suddenly from the sea, close to shore, and launch bombers which could attack the mainland.

It was so enormous that it carried a crew of 157 men and three Aichi M6A Seiran floatplane bombers, which were housed in a 35-metre long by three-metre diameter, water-tight hangar.

These aircraft were stored with their wings folded in, then rolled out through the enormous hangar door and launched by an 26-metre pneumatic catapult.  All three planes could be launched in approximately 45 minutes.

In theory, the Seirans would then complete their bombing missions, return and land on the sea next to the submarine (they were, after all, float planes), then be picked up by an onboard hydraulic crane and returned to the sub, which would in turn disappear beneath the waves.

Perhaps even more remarkably, the Sentoku had a range of 59,545 kilometres, and could travel around the world 1.5 times before needing to be refueled.  This capacity remains unmatched to this day by any diesel-electric submarine.

It also had an extremely advanced rubberized coating designed to keep it relatively undetectable by Allied sonar.

So, why isn’t the I-400 class better known? Quite simply, it’s because they never had a chance to participate in the war.

I-400 and I-401 were on their way to their first engagement at the Ulithi Atoll in August 1945, but before they arrived the war ended with the bombings of Hiroshima and Nagasaki.

Their Seiran bombers were pushed into the sea to escape American capture, but the two subs were seized on Aug. 28, 1945 and returned to Sasebo. There a number of Japanese subs were sunk, including the I-402, but I-400 and I-401 were then sailed to Hawaii for the American Navy to examine.

A year later, they were deliberately torpedoed and sank to the bottom of the sea. There was great concern that the Soviets might get their hands on this technology and use it to their advantage in the nascent Cold War.

The remains of I-401 were found again in 2005 and those of the I-400 in August 2013, close to the location of the USS Kailua.

A single Seiran plane survives today in the National Air and Space Museum in Washington D.C., the only visible remnant of a unique piece of largely forgotten naval history.

•••

Kate Humble is an historian and the Education Curator for the Maritime Museum of British Columbia. Questions and comments can be directed to: khumble@mmbc.bc.ca.

 

 

Get local stories you won't find anywhere else right to your inbox.
Sign up here

Just Posted

Bill Almond’s observatory in its new home on a Saanich lakeside. (Submitted/Cameron Burton)
Colwood stargazing dome makes a move to Saanich

The backyard structure finds a new home after 30 years

Chris Grzywacz, development agent for cannabis supplier Seed and Stone’s, holds products from the new Songhees Cannabis S + S store on April 20. (Jake Romphf/ News Staff)
First cannabis store opens on Songhees Nation, creates economic opportunity says chief

The Songhees Cannabis S + S had a soft launch at its 1502 Admirals Road location on April 20

A convicted sex offender, whose crimes included offences against children, was arrested at Gonzales Beach after the man was spotted by an off-duty officer. (Black Press Media file photo)
Convicted sex offender arrested at Gonzales Beach

After committing crimes involving children, offender barred from public beaches, being in proximity to kids

VicPD asks anyone who sees Daniel Shumka, or with information on his whereabouts to call 250-995-7654 or report anonymously through Greater Victoria Crime Stoppers at 1-800-222-8477. (Courtesy VicPD)
Victoria police seek man wanted on drug trafficking charges

Daniel Shumka, 50, is 6’1” and about 195 pounds with short brown hair and brown eyes

Victoria police arrested three men following a double stabbing April 19. The two victims suffered non-life-threatening injuries. (Black Press Media file photo)
Three arrested after double stabbing in Victoria

Two people sent to hospital after being stabbed, hit with bear spray

FILE – NDP Leader John Horgan, right, and local candidate Mike Farnworth greet one another with an elbow bump during a campaign stop in Coquitlam, B.C., on Friday, September 25, 2020. THE CANADIAN PRESS/Darryl Dyck
B.C. won’t be using random individual road stops to enforce travel rules: Safety Minister

Minister Mike Farnworth says travel checks only being considered at major highway junctions, ferry ports

A man pauses at a coffin after carrying it during a memorial march to remember victims of overdose deaths in Vancouver. THE CANADIAN PRESS/Darryl Dyck
B.C. announces historic half-billion-dollar funding for overdose crisis, mental health

Of it, $152 million will be used to address the opioid crisis and see the creation of 195 new substance use treatment beds

Children’s backpacks and shoes are seen at a CEFA (Core Education and Fine Arts) Early Learning daycare franchise, in Langley, B.C., on Tuesday May 29, 2018. THE CANADIAN PRESS/Darryl Dyck
B.C. budget to expand $10-a-day child care, but misses the mark on ‘truly universal’ system

$111 million will be used to fund 3,750 new $10-a-day spaces though 75 additional ChildCareBC universal prototype sites over the next three years.

Mak Parhar speaks at an anti-mask rally outside the Vancouver Art Gallery on Sunday, Nov. 1, 2020. Parhar was arrested on Nov. 2 and charged with allegedly violating the Quarantine Act after returning from a Flat Earth conference held in Geenville, South Carolina on Oct. 24. (Flat Earth Focker/YouTube.com screenshot)
Judge tosses lawsuit of B.C. COVID-denier who broke quarantine after Flat Earth conference

Mak Parhar accused gov, police of trespass, malfeasance, extortion, terrorism, kidnapping and fraud

Ambulance paramedic in full protective gear works outside Lion’s Gate Hospital, March 23, 2020. Hospitals are seeing record numbers of COVID-19 patients more than a year into the pandemic. (The Canadian Press)
B.C.’s COVID-19 infection rate declines, 849 cases Tuesday

Up to 456 people now in hospital, 148 in intensive care

Christy Clark, who was premier from 2011 to 2017, is the first of several present and past politicians to appear this month before the Cullen Commission, which is investigating the causes and impact of B.C.’s money-laundering problem over the past decade. (Darryl Dyck/Canadian Press)
Christy Clark says she first learned of money-laundering spike in 2015

The former B.C. premier testified Tuesday she was concerned the problem was ‘apparently at an all-time high’

Most Read