A vessel believed to be the Imperial Japanese Navy's I-402 submarine (pictured) has been discovered on the seafloor off the Goto Islands, Nagasaki Prefecture.
The Japan Coast Guard confirmed the outline of the submarine in July, and NTV crews filmed footage of it this month.
The approximately 120-meter-long I-402 was the largest submarine to operate during World War II, capable of carrying three bomber planes.
However, it did not participate in any attacks and was scuttled by the U.S. military after the war ended.
This is the first confirmation of the submarine's location, although it was known to have been scuttled off the Goto Islands.
The submarine's development is said to have started under the leadership of Isoroku Yamamoto, commander-in-chief of the combined fleet.
There were reportedly plans to use it to attack the U.S. mainland.
The I-400 and I-401, submarines of the same type as I-402, were sortied in July 1945, but the war came to an end before they participated in any attacks.
I-402 was completed in the same month but was not deployed. All the submarines were seized by the U.S. military after the war.
I-400 and I-401 were sunk off Hawaii, while I-402 was submerged off the Goto Islands with 23 other submarines in April 1946.
The JCG spotted the outline of the submarine at a depth of about 200 meters while investigating the area's seabed.
What appear to be a catapult for launching bombers and a crane for storing them are visible in the video footage taken by NTV.
"Considering some of the features, it's highly likely to be the I-402 submarine," said Junya Katsume, an expert on the history of the Imperial Japanese Navy.