Maritime Archaeology/Marine Heritage
I-400: Largest diesel submarine ever built, found off
of Barbers Point, Aug 2013.
A World War II-era Imperial Japanese
Navy mega-submarine, the I-400, lost since 1946 when it
was intentionally scuttled by U.S. forces after its
capture, has been discovered in more than 2,300 feet of
water off the southwest coast of Oʻahu. The discovery
resolves a decades-old Cold War mystery of just where
the lost submarine lay, and recalls a different era as
one war ended and a new, undeclared conflict emerged.
Longer than a football field at 400
feet, the I-400 was known as a "Sen-Toku" class
submarine-the largest submarine ever built until the
introduction of nuclear-powered subs in the 1960s. With
a range of 37,500 miles, the I-400 and its sister ship,
the I-401, were able to travel one and a half times
around the world without refueling, a capability that,
to this day, has never been matched by any other
diesel-electric submarine.
The new discovery of the I-400 was led
by veteran undersea explorer Terry Kerby, Hawaiʻi
Undersea Research Laboratory (HURL) operations director
and chief submarine pilot. Since 1992, HURL has used its
manned submersibles Pisces IV and Pisces V to hunt for
submarines and other submerged cultural resources as
part of the National Oceanic and Atmospheric
Administration's (NOAA) maritime heritage research
effort.
Heritage properties like historic
wreck sites are non-renewable resources possessing
unique information about the past. This discovery was
part of a series of dives funded by a grant from NOAA's
Office of Exploration and Research and the University of
Hawaiʻi at Mānoa's School of Ocean and Earth Science and
Technology (SOEST). Working with Steven Price of HURL,
Kerby has researched the subject of lost submarines off
Oʻahu for decades. On these recent dives, Kerby was
joined by two NOAA archaeologists with experience in
documenting World War II vessels and submarines, Drs.
James Delgado and Hans Van Tilburg.
"The I-400 has been on our 'to-find'
list for some time. It was the first of its kind of only
three built, so it is a unique and very historic
submarine,"" said Kerby. "Finding it where we did was
totally unexpected. All our research pointed to it being
further out to sea. The multi-beam anomalies that appear
on a bottom survey chart can be anything from wrecks to
rocks-you don't know until you go there. Jim and Hans
and I knew we were approaching what looked like a large
wreck on our sonar. It was a thrill when the view of a
giant submarine appeared out of the darkness."
The I-400 and the I-401
aircraft-carrying submarines held up to three
folding-wing float-plane bombers that could be launched
by catapult just minutes after the submarines surfaced.
Each aircraft could carry a powerful 1,800-pound bomb to
attack the U.S. mainland. But neither was ever used for
its designed purpose, their missions curtailed by the
end of armed conflict in the Pacific.
"The innovation of air strike
capability from long-range submarines represented a
tactical change in submarine doctrine," said Delgado,
director of NOAA's Maritime Heritage Program, within the
Office of National Marine Sanctuaries, Washington, D.C.
"The large I-400, with its extended range and ability to
launch three M6A1 Seiran strike aircraft, was clearly an
important step in the evolution of submarine design."
Up until the Sen-Toku's day,
submarines had been almost exclusively dedicated to
sinking surface ships (and other submarines) by stealth
attack from under water.
"The I-400 is technologically
significant due to the design features associated with
its large watertight hangar," Delgado said. "Following
World War II, submarine experimentation and design
changes would continue in this direction, eventually
leading to ballistic missile launching capabilities for
U.S. submarines at the advent of the nuclear era."
At the end of WWII, the U.S. Navy
captured five Japanese subs, including the I-400, and
brought them to Pearl Harbor for inspection. When the
Soviet Union demanded access to the submarines in 1946
under the terms of the treaty that ended the war, the
U.S. Navy sank the subs off the coast of Oʻahu and
claimed to have no information on their precise
location. The goal was to keep their advanced technology
out of Soviet hands during the opening chapters of the
Cold War. HURL has now successfully located four of
these five lost submarines.
The HURL crew identified the wreck
site by carefully combing through side-scan sonar and
multi-beam sonar data to identify anomalies on a deep
sea floor littered with rocky outcrops and other debris.
The wreck was positively identified as the I-400 based
on features including its aircraft launch ramp, deck
crane, torpedo tube configuration, and stern running
lights. The remains of the submarine's aircraft hangar
and conning tower appear to have been separated from the
wreck, perhaps in the blunt trauma of the three U.S.
Navy torpedo blasts that sunk the ship in 1946.
The I-400 was discovered in August
2013 and is being announced today after NOAA has
reviewed its findings with the U.S. state department and
Japanese government officials.
"These historic properties in the
Hawaiian Islands recall the critical events and
sacrifices of World War II in the Pacific, a period
which greatly affected both Japan and the United States
and shaped the Pacific region as we now know it," said
Van Tilburg, maritime heritage coordinator for NOAA in
the Pacific Islands region. "Our ability to interpret
these unique weapons of the past and jointly understand
our shared history is a mark of our progress from
animosity to reconciliation. That is the most important
lesson that the site of the I-400 can provide today."
Photos below are courtesy of John M
Johnson GM3, U.S. Crewmember of I-400. Submitted by his
son.
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