Finding Japan's Aircraft-Carrier Sub - NYTimes.com Noaa Hurl Archives The wreck of the I-400, a huge World War II submarine that was built by Japan and intended to attack the Panama Canal, was found off Hawaii by submersible Pisces V. It could just as easily have been a rock. Instead, what the crew of the submersible Pisces V found on the sea floor off Hawaii in August was a huge Japanese submarine that the United States sent to the bottom of the ocean in 1946, lest it become a Cold War trophy for the Soviet Union. The submarine, the I-400, was one of five that met a similar fate; some of the others have already been discovered. But Terry Kerby, the longtime operations director and chief submarine pilot for the Hawaii Undersea Research Laboratory, or HURL, called this one "the real prize." Besides being the first of its class, it has particular historic value. "This one actually trained for a mission: Attack the Panama Canal," Mr. Kerby said. The megasub was remarkable for its size alone: 400 feet, nearly twice as long as a standard German U-boat of the time. More important, it could serve as an underwater aircraft carrier, carrying up to three folding-wing M6A1 Seiran bombers. "At the time this thing was sunk, it and its sister ship were the most advanced submarines in the world," said James P. Delgado, director of the National Oceanic and Atmospheric Administration's maritime heritage program and one of two marine archaeologists aboard the Pisces V when it came upon the I-400 wreck, 2,300 feet down. Word of the Aug. 1 discovery, which was announced Monday in a University of Hawaii news release, was withheld until the State Department and Japanese government could be informed. The five submarines captured by the Navy, among the last remnants of the Imperial Japanese fleet, were taken back to Pearl Harbor for inspection. But under the treaty that ended the war in the Pacific, any military technology acquired from Japan was to be made available to other Allied powers, including the Soviet Union. Sensing that United States-Soviet relations were already tense, however, the Navy decided to scuttle the vessels off the coast of Oahu rather than offer a rival access to such advanced technology. "More time could have been spent documenting them, but there was a Cold War beginning," Dr. Delgado said. It was important to get those subs on the bottom and keep them out of the hands of the Soviets. The government's official line, that the five subs had been used for target practice and that the precise locations of the wrecks were unknown, has been corroborated by since-declassified Navy documents, Dr. Delgado said. "The position that was given was miles away," he said. They were more interested in just sinking it and getting it out of the way. Federal funding cuts have driven HURL's submarine pilots to capitalize on every moment underwater, including commercial research excursions paid for by other organizations. For years while conducting these science dives - HURL's bread and butter, for the most part - Mr. Kerby has discreetly made note of points of interest on the ocean floor to revisit whenever the opportunity might arise. "In his back pocket, Terry always has a list of things: a sonar contact, something of that sort that might turn out to be an interesting find," Dr. Delgado said. He wanted to find the I-400. Often the sea-floor irregularities that catch Mr. Kerby's interest turn out to be nothing more than rocks, carbon formations or debris. On the morning of Aug. 1, however, one of his hunches was validated. "There was an anomaly up to the north that was very possibly a wreck," he said, but it was a long way from where they thought the I-400 was actually sunk. So when we came up and this giant bow came out of the dark, this submarine, it was a surprise to find it where we did. But it was a thrill. The three men aboard the Pisces V were guardedly optimistic about their find. "As we approached it from the sonar the excitement built, and suddenly there you were, at the mangled bow of a submarine," Dr. Delgado said. But it wasn't readily apparent that we were on I-400 until we really started to go through it piece by piece and match things up. "It wasn't an immediate high-five," he said. As for what awaits the I-400, its present resting place will probably be permanent. There are no plans to bring any of the wreckage to the surface. "In cases like this, when you find historic shipwrecks, what you've done is not just something archaeological," Dr. Delgado said. You have added into the catalog of the world's greatest museum: the bottom of the seas.