Two World War II Japanese submarines, designed with revolutionary technology to attack the U.S. mainland, have been discovered off the Hawaiian coast of Oahu. They each carried two aircraft while submerged and were the fastest attack subs of WWII.
The announcement of the discovery was made by the National Oceanic and Atmospheric Administration’s (NOAA’s) Undersea Research Lab at the University of Hawai‘i at Manoa and by National Geographic Channel (NGC), which documented and partly funded the search mission for an upcoming special documentary.
The subs, intended as part of a top-secret plan by the Imperial Japanese Navy to attack the U.S. mainland, including New York City and Washington, D.C., were last seen in 1946 when the American Navy intentionally sunk them, reportedly to keep their advanced technology out of Soviet hands during the opening chapters of the Cold War.
Since 1992, the Hawaii Undersea Research Laboratory has used the manned submersibles Pisces IV and Pisces V during test and trial dives to hunt for the submarines and other lost maritime heritage artifacts. In March 2005, the I-401, which carried three aircraft, was the first submarine located. Its discovery was publicly announced that same year. The I-400, sister ship to the I-401, remains undiscovered. The I-14 and the I-201 attack submarines ? which were both capable of staying submerged for up to a month ? were discovered in February 2009.
Longer than a football field at 400 feet, the I-400 “Sen-Toku” class were the largest submarines ever built until the introduction of nuclear-powered submarines in the 1950s. With a range of 37,500 miles, they were able to go one and a half times around the globe without refueling, a capability that, to this day, has never been matched by any other diesel-electric submarine.
At the end of WWII, the U.S. Navy captured the subs and had exclusive access to their technology. When the Soviet Union demanded access in 1946 under the terms of the treaty that ended the war, the U.S. Navy sunk the subs off the coast of Oahu and claimed to have no information on their precise location.