The Sen Toku I-400-class (伊四〇〇型潜水艦)
submarineA submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has only limited underwater capability...
s of the
Imperial Japanese NavyThe Imperial Japanese Navy , literally Navy of the Empire of Greater Japan was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes...
were the largest submarines of
World War IIWorld War II, or the Second World War , was a global military conflict which involved a majority of the world's nations, including all great powers, organized into two opposing military alliances: the Allies and the Axis...
, and remained the largest ever built prior to the development of nuclear ballistic missile submarines in the 1960s. They were
submarine aircraft carrierSubmarine aircraft carriers are submarines equipped with fixed wing aircraft for observation or attack missions. These submarines saw their most extensive use during World War II, although their operational significance remained rather small...
s able to carry three
Aichi M6AThe Aichi M6A Seiran was a submarine-launched attack floatplane designed for the Imperial Japanese Navy.-Design and development:...
Seiran aircraft underwater to their destinations. They were designed to surface, launch the planes then dive again quickly before they were discovered. They also carried
torpedoThe modern torpedo is a self-propelled explosive projectile weapon, launched above or below the water surface, propelled underwater toward a target, and designed to detonate on contact or in proximity to a target...
es for close range combat.
The I-400
class was designed with the range to travel anywhere in the world and return. A fleet of 18 boats was planned in 1942, and work started on the first in January 1943 at the Kure, Hiroshimais a city located in Hiroshima prefecture, Japan.As of January 1, 2008, the city has an estimated population of 246,118 and a density of 696 persons per km². The total area is 353.74 km².- History :...
arsenal. Within a year the plan was scaled back to five, of which only three (I-400
at Kureis a city located in Hiroshima prefecture, Japan.As of January 1, 2008, the city has an estimated population of 246,118 and a density of 696 persons per km². The total area is 353.74 km².- History :...
, and I-401
The Sen Toku-class I-401 was once the largest submarine in the world. It was commanded by Lieutenant Commander Nambu. Capable of carrying three two-seat Aichi M6A1 "Seiran" float torpedo bombers, the Sen Tokus were built to launch a surprise air strike against the Panama Canal.-Service...
and I-402 at Sasebo) were completed.
Characteristics
Each submarine had four 3,000
horsepowerHorsepower is the name of several non-SI units of power. It was originally defined to allow the output of steam engines to be measured and compared with the power output of draft horses. The horsepower was widely adopted to measure the output of piston engines, turbines, electric motors and other...
(2.2 MW) engines and carried enough fuel to go around the world one-and-a-half times—more than enough to reach the United States traveling east or west. They displaced 6,500 tons and were over 400 feet (120 m) long, three times the size of the typical submarines of the time. They had a figure-eight hull shape affording additional strength to handle the on-deck hangar for housing the three aircraft. They also had four anti-aircraft guns, a large deck gun, and eight torpedo tubes.
They were able to carry three
Aichi M6A SeiranThe Aichi M6A Seiran was a submarine-launched attack floatplane designed for the Imperial Japanese Navy.-Design and development:...
aircraftAn aircraft is a vehicle which is able to fly by being supported by the air, or in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil An aircraft is a vehicle which is able to fly by being supported...
, each carrying an 800 kilogram (1,764 lb) bomb 650 miles (1000 km) at 295 miles per hour (474 km/h). The existence of the Seiran was unknown to Allied intelligence. The wings of the Seiran folded back, the horizontal stabilizers folded down, and the top of the vertical stabilizer folded over so the overall forward profile of the aircraft was within the diameter of its propeller. When prepared for flight, they had a wing span of 40 feet (12 m) and a length of 38 feet (11.6 m). A crew of four could prepare and get all three airborne in 45 minutes. The planes were launched from a 120-foot (37-m)
catapultAn aircraft catapult is a device used to launch aircraft from ships—in particular aircraft carriers—as a form of assisted take off. It consists of a track built into the flight deck, below which is a large piston or shuttle that is attached through the track to the nose gear of the aircraft.Older...
on the deck of the giant submarine. A restored Seiran airplane is displayed at the
National Air and Space MuseumThe National Air and Space Museum of the Smithsonian Institution is a museum in Washington, D.C., United States, and is the most popular of the Smithsonian museums. It maintains the largest collection of aircraft and spacecraft in the world...
in
Washington, D.C.Washington, D.C. , formally the District of Columbia and commonly referred to as Washington, the District, or simply D.C., is the capital of the United States, founded on July 16, 1790...
. Only one was ever recovered and it had been ravaged by weather and souvenir collectors, but the restoration team was able to reconstruct it accurately.
The I-402 was completed immediately before the war ended, but had been converted during building to a tanker and was never equipped with aircraft.
Operational history
As the war turned against the Japanese and their fleet no longer had free rein in the Pacific, the Commander-in-Chief of the Japanese Combined Fleet,
Admiral Isoroku YamamotoNaval Marshal General was the commander-in-chief of the Combined Fleet during World War II, a graduate of the Imperial Japanese Naval Academy and a student of the U.S...
, devised a daring plan to attack the cities of
New YorkNew York is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous. The state is bordered by New Jersey and Pennsylvania to the south, and Connecticut, Massachusetts and Vermont to the east...
, Washington D.C., and other large American cities as well as to destroy the
Panama CanalThe Panama Canal is a ship canal which joins the Caribbean Sea to the Pacific ocean. One of the largest and most difficult engineering projects ever undertaken, it had an enormous impact on shipping between the two oceans, replacing the long and treacherous route via the Drake Passage and Cape Horn...
.
One of Yamamoto’s plans was to use the sen toku (secret submarine attack), so that in the opening days of 1945, preparations were under way to attack the Panama Canal. The strategy was to cut the supply lines and access to the
Pacific OceanThe Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Tepre Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan. It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and...
by U.S. ships. The plan was to sail westward through the
Indian OceanThe Indian Ocean is the third largest of the world's oceanic divisions, covering about 20% of the water on the Earth's surface. It is bounded on the north by South Asia ; on the west by Africa; on the east by Indochina, the Sunda Islands, and Australia; and on the south by the Southern Ocean...
, around the southern tip of
AfricaAfrica is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the...
, and attack the canal’s Gatun Locks from the east, a direction from which the Americans would not expect an attack and would be ill-prepared to defend. The flights would, of course, be one-way trips. None of the pilots expected to survive the attack, a tactic called
tokkoDuring World War II, , also abbreviated to 特攻隊, tokkōtai), also called shimbu-tai by the Imperial Japanese Army, were specialized units normally used for suicide missions...
. Each pilot was presented with a tokko short sword, symbolic of the ultimate sacrifice.
Before the attack could commence from the Japanese naval base at Maizuru, word reached Japan that the Allies were preparing for an assault on the home islands. The mission was changed to attack the Allied naval base on
UlithiUlithi is an atoll in the Caroline Islands of the western Pacific Ocean, about 191 km east of Yap. It consists of 40 islets totalling , surrounding a lagoon about long and wide—at the fourth largest in the world. It is administered by the state of Yap in the Federated States of Micronesia....
where the invasion was being assembled. Before that could take place, the Emperor announced the surrender of Japan.
On August 22, 1945, the crews of the submarines were ordered to destroy all their weapons. The torpedoes were fired without arming and the aircraft were launched without unfolding the wings and stabilizers. When I-401
surrendered to an American destroyer, the U.S. crew was astounded at its size.
American inspections
The U.S. Navy boarded and recovered 24 submarines including the three I-400
submarines, taking them to Sasebo Bayis a city located in Nagasaki Prefecture, Japan. As of 2009, the city has an estimated population of 252,698 and the density of 694 persons per km². The total area is 364 km². The locality is famed for its scenic beauty. The city includes a part of Saikai National Park...
to study them. While there, they received a message that the Soviets were sending an inspection team to examine the submarines. To keep the technology out of the hands of the Soviets, Operation Road’s End
was instituted. Most of the submarines were taken to a position designated as Point Deep Six, about 40 miles (60 km) west of Nagasaki and off the Gotō IslandsThe , literally: "five-island archipelago") are Japanese islands in the East China Sea, off the western coast of Kyūshū. The islands are a part of Nagasaki Prefecture...
, were packed with charges of C-2 explosive and destroyed. They are today at a depth of 200 meters.
Four remaining submarines (I-400
, I-401
, I-201
The I-201-class submarines were submarines of the Imperial Japanese Navy during World War II. These submarines were of advanced design, built for high underwater speed, and were known as Senkou...
and I-203
The I-201-class submarines were submarines of the Imperial Japanese Navy during World War II. These submarines were of advanced design, built for high underwater speed, and were known as Senkou...
) were sailed to Hawaii by U.S. Navy technicians for further inspection. Upon completion of the inspections, the submarines were scuttledScuttling is the act of deliberately sinking a ship by allowing water to flow into the hull. This can be achieved in several ways – valves or hatches can be opened to the sea, or holes may be ripped into the hull with brute force or with explosives...
in the waters off Kalaeloa near OahuOahu or Oahu , known as "The Gathering Place", is the third largest of the Hawaiian Islands and most populous of the islands in the State of Hawaii. The state capital Honolulu is located on the southeast coast...
in HawaiiHawaii is the newest of the 50 U.S. states, and is the only state made up entirely of islands. It is located on an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of Australia. The state was admitted to the Union on August...
by torpedoes from US submarine on June 4, 1946, apparently because Soviet scientists were again demanding access to them. The wreckage of I-401
was rediscovered by the Pisces
deep-sea submarines of the Hawaii Undersea Research Laboratory in March 2005 at a depth of 820 meters.
See also
- AM type submarine—IJN two-aircraft submarine seaplane tender
- Submarine aircraft carrier
Submarine aircraft carriers are submarines equipped with fixed wing aircraft for observation or attack missions. These submarines saw their most extensive use during World War II, although their operational significance remained rather small...
- French submarine
Surcouf
External links
I-400
WW2DB: I-400-class Submarines
I-400
I-401
I-402
Discovery of I-401
wreckage off Hawai
Hawai Undersea Research Laboratory report
A Damn Interesting article
Story of the transpacific voyage of I-400
Japan's WWII Monster Sub: How the deadly Sen-Toku mission almost succeeded
The Sen-Toku Raid
— review of novel by John Mannock about I-400-class submarine
I-400