I-400-class submarine
| File:I-400.jpg I-400, with its long plane hangar and forward catapult. | ||
| Career | RN Ensign | |
|---|---|---|
| Ships: | I 400, I 401, I 402 | |
| Completed: | 1944-45 | |
| Decommissioned: | 1945 | |
| Fate: | Scuttled in the Pacific by the US Navy, 1946 | |
| General Characteristics | ||
| Displacement: | 5,223 tons / 6,560 tons | |
| Dimensions: | 400.3 x 39.3 x 23 ft (122 x 12.0 x 7.0 m) | |
| Surface propulsion: | 4 diesels: 7,700 hp (5.7 MW) | |
| Submerged propulsion: | Electric motors: 2,400 hp (1.8 MW) | |
| Surface speed: | 18.75 knots (35 km/h) | |
| Submerged speed: | 6.5 knots (12 km/h) | |
| Maximum depth: | 100 m (330 ft) | |
| Range: | 37,500 nautical miles (69,500 km) at 14 knots (26 km/h) | |
| Complement: | 144 | |
| Armament: | 3 Aichi M6A1 Seiran sea-planes 8 x 533 mm forward torpedo tubes |
|
The Sen Toku I-400 class (伊四〇〇型潜水艦) submarines of the Imperial Japanese Navy were the largest submarines of WW2, the largest non-nuclear submarines ever constructed, and the largest in the world until the development of nuclear ballistic submarines in the 1960s. These were submarine aircraft carriers and each of them was able to carry 3 Aichi M6A Seiran aircraft underwater to their destinations. They also carried torpedoes for close range combat and were designed to surface, launch the planes then dive again quickly before they were discovered.
The I-400 was originally designed so that it could travel round-trip to anywhere in the world, and it was specifically intended to destroy the U.S.-controlled Panama Canal. A fleet of 18 boats was planned in 1942, and work on the first one was started in January 1943 at the Kure, Hiroshima arsenal. Within a year the plan was scaled back to five, and only three (the I-400 at Kure, and the I-401 and I-402 at Sasebo) were completed.
Although the U.S. Navy remained discreet about it, the Japanese were ahead of the Allies in many aspects of submarine development and underwater weapons. During the Second World War, the Japanese had 30 different classes of submarines — from the one-man suicide torpedoes to the giant I-400 class of aircraft carriers, and used the world's most efficient torpedoes, the Long Lance.
Characteristics
Each submarine had four 3,000 horsepower (2.2 MW) engines and fuel enough to go around the world one-and-a-half times, more than enough to reach the United States from either direction. It displaced 6,500 tons and was over 400 feet (120 m) long, three times the size of ordinary submarines. It had a figure-eight hull shape for additional strength to handle the on-deck hangar for housing the three aircraft. In addition, it had four antiaircraft guns and a large deck cannon as well as eight torpedo tubes from which they could fire the Long Lance.
They were able to carry three 3 Aichi M6A seiran aircraft, each carrying an 800 kilogram (1,764 lb) bomb 650 miles (1000 km) at 360 miles per hour (580 km/h). Its name was combination of sei (clear sky) and ran (storm), literally “storm out of a clear sky,” because the Americans would not know they were coming. The existence of the seiran class of aircraft 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 propellor. 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) catapult on the deck of the giant submarine. A restored seiran airplane is on exhibit in the National Air & Space Museum in the Smithsonian Institute. 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.
Operational history
As the war turned against the Japanese and their fleet no longer had free reign over the Pacific, the Commander-in-Chief of the Japanese Combined Fleet, Admiral Isoroku Yamamoto, devised a daring plan to attack the cities of New York, Washington D.C., and other large American cities as well as to destroy the Panama Canal.
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 by U.S. ships. The plan was to sail westward through the Indian Ocean, around the southern tip of Africa, and attack the canal’s Gatun Locks from the east, a direction from which the Americans would not expect and were little prepared to defend. The flights would, of course, be one-way trips. None of the pilots expected to survive the attack, a tactic called tokko. 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 Ulithi 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 sei ran aircraft were launched without unfolding the wings and stabilizers. When the I-401 surrendered to an American destroyer, the U.S. crew was astounded at its size. The commander of the submarine fleet, Captain Ariizumi, had been responsible for an atrocity earler in the war and therefore apparently decided on suicide rather than surrender to the Americans. He requested that his body be wrapped in the Japanese flag and buried at sea. He then shot himself. His body was never presented as proof of his death.
American inspections
The U.S. Navy boarded and recovered 24 submarines including the three I-400 submarines, taking them to Sasebo Bay 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 from Nagasaki and off the island of Goto-Rettō, were packed with charges of C-2 explosive and destroyed.
Four remaining submarines (I 400, I 401, I 201 and I 203 which achieved speeds double those of American submarines), were sailed to Hawai by US Navy technicians for further inspection. Upon completion of the inspections, the submarines were scutled in the waters off Kalaeloa near Oahu in Hawaii by torpedoes from the American submarine USS Cabezon on May 31, 1946. The reason for the scuttling is apparently that Russian scientists were again demanding access to the submarines. The wreckage of I 401 was re-discovered by the Pisces submarines deep-sea submarines of the Hawaii Undersea Research Laboratory in March 2005 at a depth of 820 meters.
Post-War influences
It is sometimes suggested that the sen toku inspired the building of the large modern nuclear submarines and that the launching of aircraft from a submarine lead to the idea of launching ballistic missiles. This has been disputed because the largest submarines ever, the Russian Typhoon class, was built in ignorance of the sen toku. As early as the Second World War, US submarines had fired rockets from deck-mounted launchers against the Japanese mainland (the Japanese thought they were bombs from high-flying night bombers). Incidentally, the hulls of modern nuclear submarines do not feature the figure-eight shape of the sen toku, but were based on the shape of the German Walther boats that were developed toward the end of the war (The Germans themselves based their design on the shape of dolphins.)