Japanese WWII-era aircraft-carrying sub found off Oahu

HONOLULU — Days ahead of the Pearl Harbor bombing's anniversary, University of Hawaii researchers announced they've found a massive, sunken World War II-era Japanese submarine in deep water southwest of Oahu.

The I-400, an aircraft-carrying submarine and one of the largest of its era, was captured by U.S. military forces after the war ended. The Navy then intentionally torpedoed the craft (with nobody aboard) in 1946 so its cutting-edge design would not fall into Soviet hands at the dawn of the Cold War.

It was among five Empire of Japan-surrendered submarines that the Navy sank off Barbers Point that year, once the U.S. had a chance to study the Japa­nese innovations.

"There's a lot of history on the bottom, off of South Oahu," said Terry Kerby, chief submarine pilot for UH's Hawaii Undersea Research Lab. He and two other researchers found the 400-foot-long submarine, a relic of World War II and the burgeoning Cold War, during a test dive in August of HURL's deep-sea submersible, the Pisces V.

They visited the location, more than 2,300 feet below the surface, after sonar mappings of the seafloor showed a sunken vessel might be there. They then made the discovery public Monday after spending several months consulting with the U.S. State Department and the Japanese government, they said.

"Things can look like a shipwreck, but you never know until you put eyes on it," James Delgado, NOAA's director of maritime heritage, said Monday. He was with Kerby in the Pisces V when the discovery was made. "It was a real thrill to see that bow coming out of the dark."

Once torpedoed, the submarine had clearly slammed nose-first into the seafloor, Delgado said. Its bow was badly damaged, and its distinctive airtight hangar, once used to house up to three bomber planes with foldable wings, was missing, Delgado said.

However, the group identified the I-400 by its aircraft launch ramp, deck crane and other features, according to a UH news release.

The Japanese had considered using the submarine to bomb the Panama Canal during World War II but later opted against that, Delgado said. Its hangar design helped usher in Cold War-era innovations, and the nuclear-powered and weaponized submarines that emerged in the 1960s, he added.

HURL has now found four of the five Japa­nese submarines that the Navy sank off Barbers Point since its search began in 2005, Kerby said. The one that remains missing, the I-203, was a sleek, 200-foot-long submarine built for speed and not to carry airplanes, he added.

Retired Navy Lt. Cmdr. Allen B. "Buck" Catlin, who served in the Pacific during World War II, played a key role in sinking those submarines. Catlin helped bring the vessels to Oahu and grasp their technology.

"It's an interesting history, the end of the Japanese fleet," Catlin, 95, said in a phone interview Monday from the Los Angeles area. Catlin said he met the vessels' Japa­nese crew in Japan and that they were "very cooperative" in helping the U.S. forces understand their submarines' capabilities.

Catlin said he wished at least one of the submarines could have been saved instead of sunk.

HURL researchers have found some 140 historic wreck sites along South Oahu since 1992, when they started using their test dives to visit sites believed to have sunken vessels, Kerby said.

The recent federal government shutdown helped delay the announcement of I-400's discovery until December, Delgado said. There have been no additional visits to the site since its discovery, and no immediate plans to return, he added.

However, uncovering its whereabouts could help inspire others to explore and become more interested in history, Delgado said.

"Something like this has us thinking about the oceans, about technology and innovation — about war and sacrifice," Delgado said Monday. "The final frontier doesn't only exist in space. It's here, in these oceans."

Star-Advertiser reporter William Cole contributed to this report.

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