WWII submarine found: what it was doing in underwater 'trash heap' off Hawaii

WWII submarine built by Japan to transport bomb-carrying planes to within striking distance of New York was captured by the US. The WWII submarine was studied and scuttled before the Soviets could get a good look.

Hawaii Undersea Research Laboratory (HURL) photo shows a submerged Japanese I-400 submarine discovered off the coast of Oahu, Hawaii in August 2013.

For 67 years, one of the most remarkable warships to ply the Pacific during World War II has lain beneath 2,300 feet of water somewhere off the Hawaiian island of Oahu.

Now, marine archaeologists say they have located the vessel – a 400-foot long Japanese submarine that carried three single-engine aircraft tucked in its hangar and enough fuel to circumnavigate the Earth 1-1/2 times non-stop.

Japan's 400-class subs represented the largest ever built until well into the 1960s.

The newfound sub, designated I-400, was the first of 18 similar subs the Japanese Navy planned to build, although only three were completed. Their mission, never realized, was to take Japan's fight against the United States to US shores, initially by unleashing their planes, each carrying one 1,800-pound bomb, on New York City.

Their size, technology, and their missions have anointed these vessels with almost mythical status among naval historians of World War II, says James Delgado, who heads the Maritime Heritage Program at the National Oceanic and Atmospheric Administration's Office of Marine Sanctuaries in Washington.

The discovery was announced Monday, but historians have long known about the subs, and the Navy hastily examined all three after their captains surrendered them. The I-400's sister sub, the I-401, also was found off Oahu in 2005. But discovering such vessels again – especially the first of a class – after decades of uncertainty about where they rest is important, Dr. Delgado says.

“The oceans are the biggest museum we have,” he says. “Whenever we find one of these things, it takes it out of the books, or off of the Internet if you will, and makes it real again.”

Japan was not the first country to consider using submarines as platforms for launching airplanes. During World War I, the Germans balanced a single-engine seaplane on the forward deck of a surfaced submarine. When the sub partially submerged, the seaplane floated away and took off – a proof of concept that was deemed impractical, in no small part because sub and seaplane were vulnerable to bad weather and well-placed rounds from an enemy ship.

Between the two World Wars, France, Italy, Britain, and the US explored the idea. But the US and Britain abandoned it after a British sub carrying a small airplane sank after water flooded in though the open hangar door. A French sub sank after it collided with a US merchant ship in the Caribbean during World War II.

Germany and Japan continued to develop the concept, however, although the planes were designed for reconnaissance.

Japan advanced the concept to carry combat aircraft, ultimately deploying three types of aircraft-bearing subs. The 400-class subs represented the most potent of the three.

“They were the brainchild of Admiral Yamamoto,” the commander-in-chief of Japan's Navy during the war, Delgado explains. “His plan is to go hit New York. His plan is to pay back the United States psychologically for the Doolittle raid on Tokyo.”

That raid, which took place in 1942, involved the launching, from an aircraft carrier, of 16 B-25 bombers designed for typical airfields on land. The raid inflicted little physical damage on Tokyo, but it boosted US morale after the debacle at Pearl Harbor and undermined the morale of the Japanese.

The Japanese also planned to have two of the mammoth subs attack the Panama Canal with the hope of destroying enough lock gates to drain the artificial lake that is critical to the canal's operation.

After the war, the US captured all three I-400 class subs, one of which had been converted into a tanker for carrying fuel. And while the terms of the agreement among the Allies at Yalta gave the Soviets access to the spoils of war captured by other countries in the Alliance, the US had no intention of letting Soviet experts pore over such advanced subs.

The converted tanker was sunk in the East China Sea in late 1945. The other two reached Pearl Harbor, where they were examined, then towed well out to sea and torpedoed in deep water. The Soviets, Delgado notes, were not happy campers.

There, the sub has rested, along with the I-401, as well as other prizes the US captured.

Indeed, Delgado says, the deep waters off of Pearl Harbor essentially represent the marine-archaeology equivalent of the kitchen trash for the US Navy.

For about a century, the US has used those waters to dump tanks, aircraft, unexploded bombs, captured prizes from naval engagements, and surplus ships it no longer needed – a 20th century version of a midden, the pile of shucked shells and gnawed or butchered bones land-based archaeologists pick through for insights into the people that left it. And many of the artifacts off of Oahu are very well preserved.

The August expedition that discovered the I-400 was led by Terry Kerby, operations director for the Hawaii Undersea Research Laboratory at the University of Hawaii and its chief submarine pilot. He, Delgado, and Hans Van Tilburg, also with NOAA, initially went out to gauge the status of two Japanese one-man mini-subs that were sunk during and after the attack on Pearl Harbor.

Unlike a captured vessel, which becomes the property of the nation that captures it, ships sunk in combat remain the property of the nation that built and deployed it. The NOAA archaeologists were making the dive to check out the subs and report back to the Japanese government on their condition.

Over the years, Mr. Kerby has systematically hunted for ships in Pearl Harbor's midden, squeezing an extra dive or two onto his minisub's agenda when out on other assignments, Delgado says.

On this occasion he recalls asking Kerby if he had anything else the archaeologists would like to see. The answer: He had a couple of targets no one had explored before, based on sonar data he had collected from various sources. The first one turned out to be the USS Kailua, a ship built in the 1920s that towed the I-400 and I-401 out to be sunk, and itself was torpedoed as unneeded postwar surplus at the same time. They gingerly traversed the darkness toward the second target.

“Slowly, out of the gloom, comes the bow,” Delgado recalls, one that clearly belongs to a submarine. “Everybody's pulse picks up.”

As the sub slowly moved along the length of the vessel, the trio noted the hull's features. After analyzing the data once they got back, they realized they'd found the I-400. Among the clinchers: the sub's unique set of eight torpedo tubes, a bow sloped to serve as a launch ramp for the aircraft, and the location of a crane designed to pluck the pontooned planes out of the ocean so they could be prepared for storage on the sub.

Delgado and his colleagues notified the State Department, and in a meeting with US and Japanese officials in Washington turned over photos of the sunken sub and explained how they had discovered it.

For Delgado, the discovery highlights the fact that much remains to be uncovered beneath the seas.

“There's still an awful lot yet to be done and to be found,” he says. “The age of exploration isn't over. It's just beginning.”

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