Dive discovers missing aircraft hangar of sunken WWII-era Japanese submarine. The dramatic discovery of a lost World War II-era Imperial Japanese Navy mega-submarine by a University of Hawaiʻi and U.S. National Oceanic and Atmospheric Administration (NOAA) team in December 2013 inspired a new search by NHK, the Japanese Broadcasting Corporation, to find key missing pieces of the battleship.
The recent survey, the first to return to I-400 submarine since its discovery, successfully located, mapped and captured on vdeo for the first time not only the submarine’s hangar and conning tower (navigation platform), but an unexpected and significant new discovery—the submarine’s bell. Torn from the submarine by the explosive forces that broke apart and sank I-400, the bell lies close to the conning tower on the seafloor.
The massive aircraft hangar, large enough to launch three float-plane bombers, was the defining feature of the I-400. After the end of the war, the I-400 was deliberately sunk at sea outside of Pearl Harbor to keep its technological innovations safe from the Soviet Union.
“We didn’t have detailed enough bottom mapping data to help locate the hangar, conning tower and other signature features missing from the wreck of the I-400,” said Terry Kerby, operations director and chief submarine pilot of the Hawaiʻi Undersea Research Laboratory (HURL). “With only one dive day to try to find anything, we knew there was a strong chance we might spend the dive looking at the barren sandy bottom.”
Kerby continued, “We made a lucky guess where to start when we approached the main hull of the I-400 from the northwest. Our guess started to pay off when the giant hangar door came into view, followed by the conning tower and hangar. Many items were amazingly intact for something that had ripped out of the hull of a sinking 400-foot-long submarine.”
The survey was conducted in cooperation with NOAA’sMaritime Heritage Program in the Office of National Marine Sanctuaries, with NOAA’s Hans Van Tilburg joining the dives as project archaeologist.
“The Office of National Marine Sanctuaries has been a partner for over a decade with HURL on many of the amazing and significant historical and archaeological discoveries they have made off Oahu,” said James Delgado, director of the Maritime Heritage Program. “The waters off Hawaiʻi not only encompass an important part of Native Hawaiian culture, but are also a veritable museum of our maritime past. As America’s ocean science agency, we’re committed to working with partners like HURL and NHK to learn more, and to share more of what lies beneath the waves.”
HURL-NHK I-400 submarine survey
The dramatic discovery of a lost World War II-era Imperial Japanese Navy mega-submarine by a University of Hawaiʻi and U.S. National Oceanic and Atmospheric Administration team in December 2013 inspired a new search by NHK, the Japanese Broadcasting Corporation, to find key missing pieces of the battleship. The recent survey, the first to return to I-400 submarine since its discovery, successfully located, mapped and captured on video for the first time not only the submarine’s hangar and conning tower (navigation platform), but an unexpected and significant new discovery – the submarine’s bell.
HURL video of I-400 initial sighting
Experience the first view of 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. It now sits in more than 2,300 feet of water off the southwest coast of O'ahu.
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.
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.