World War II-era Japanese sub discovered off Hawaii coast

Just days before the 72nd anniversary of the attack on Pearl Harbor, there's a major find for shipwreck hunters -- a massive Japanese submarine, sunk off Hawaii's shores. It could have re-written the history of World War II.

The I-400-class submarine, Chip Reid reported on "CBS This Morning, was really an underwater aircraft carrier, capable of launching Japanese bombers, just minutes after surfacing. It was state-of-the-art at the time, and its technology led to some important innovations for the U.S. Navy's own submarine fleet.

The wreckage was discovered off the coast of Oahu, nearly half-a-mile under the ocean surface. It was the culmination of decades of work by researchers at the University of Hawaii. 

The I-400's location was first identified using sonar images of the ocean floor. The team then used a submersible to get a closer look.

James Delgado, director of maritime heritage at the National Oceanic and Atmospheric Administration, helped find the wreck.

"Three of us crowded into a tiny six-foot diameter sphere and dropped into the darkness," Delgado said. "And then out of the darkness -- there it was, this huge submarine, sitting on the bottom."

The I-400 was one of only three of its kind ever built. The 400-foot-long super sub carried three bombers and was capable of sailing one-and-a-half times around the world without refueling.

It was conceived by Isoroku Yamamoto, the Japanese admiral who masterminded the attack on Pearl Harbor. He wanted to use the sub to attack major U.S. cities and the Panama Canal.

"I-400, I-401 and I-402 -- its sister subs -- never were able to carry out that mission, and at the end of the war, were caught on the high seas and surrendered, literally at gunpoint, to U.S. Navy forces," Delgado said.

The Navy studied the sub for a year before finally sinking it off the coast of Hawaii. The U.S. wanted to keep the sub's secrets and technology away from the Soviet Union -- a World War II ally that was becoming a Cold War foe.

"Ultimately, I-400 would pave the way for the next generation of American submarines -- in particular, American submarines that would take the atomic bomb to sea," Delgado said. "Because they recognized, in these subs, what they had with that undersea hanger was the ability to put not a plane, but a missile."

The discovery was made in August, but was not publicly revealed until now because the researchers needed time to confirm their findings and inform the U.S. and Japanese governments. The I-400 is likely to stay in its watery grave indefinitely. There are no plans to bring it to the surface at this point.