Japanese WWII Mega-Submarine Found Sunk Off Hawaiian Coast
December 4, 2013

Japanese WWII Mega-Submarine Found Sunk Off Hawaiian Coast

Lee Rannals for redOrbit.com - Your Universe Online

A World War II-era Imperial Japanese Navy mega-submarine has been found off the coast of Hawaii, 67 years after it was lost. The ship was discovered more than 2,300 feet below sea level near the southwest island of O'ahu.

The I-400 submarine, longer than a football field, was the largest submarine ever built until the introduction of nuclear-powered subs in the 1960s. It had a range of 37,500 miles and was able to travel one and a half times around the world without refueling, which is a capability that has never been matched by any other diesel-electric submarine to this day.

The discovery of the vessel's final resting place helps resolve 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.

Scientists using the Hawaii Undersea Research Laboratory (HURL) Pisces IV and Pisces V deep-diving manned submersibles found the I-400. This equipment has been used before to help hunt for submarines and other submerged cultural resources.

“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,” veteran undersea explorer Terry Kerby, who led the excursion, said in a statement. “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 its sister ship I-401, were aircraft-carrying submarines that 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 1,800-pound bomb to attack the US mainland. While the submarines were a deadly asset, Japan never had to use them for their designed purpose because their missions were 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,” Dr. James Delgado, director of NOAA’s Maritime Heritage Program, within the Office of National Marine Sanctuaries, Washington, DC, said in a statement. “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 emergence of I-400, submarines were designed for sinking surface ships through stealth attacks from under water. The I-400 changed the game in how a submarine could be used to attack enemies.

“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 US submarines at the advent of the nuclear era.”

When WWII ended, the US Navy captured five Japanese subs, including the I-400. The navy brought the subs to Pearl Harbor for inspection, but when the Soviet Union demanded access to the submarines in 1946 under the terms of the treaty, the US Navy sank the subs off the coast of O’ahu and claimed to have no information on their precise location.

The HURL team identified the wreckage site by carefully looking 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 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 US Navy torpedo blasts that sunk the ship in 1946.

“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,” Van Tilburg, maritime heritage coordinator for NOAA in the Pacific Islands region, said in a press release. “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.”