Story highlights Japan's I-400 submarine could carry three planes

Sub was scuttled after World War II to keep it away from Soviet Union

Hull of sub was discovered off Hawaii in 2013

(CNN) Piece by piece, the depths of the Pacific are giving up the story of World War II.

Researchers from the University of Hawaii and National Oceanic and Atmospheric Administration announced last month that they have found important pieces of a Japanese aircraft carrier submarine scuttled after the war.

The hull of the Japanese Imperial Navy's I-400 was discovered in about 2,300 feet of water off the southwest coast of Oahu in late 2013. What that dive didn't find was what made the sub so special, a hangar big enough to hold three folding-wing seaplanes.

But the find generated enough buzz that Japanese broadcaster NHK wanted to go find that hangar deck. The network went to the researchers with a plan to make one more, one-day dive.

It was gamble because researchers did not know where the hangar may have fallen when it separated from the sub. They figured they had four quadrants to search but had the time and money to search only one, according to Terry Kerby, operations director and chief submarine pilot of the Hawaiʻi Undersea Research Laboratory at the university.

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