The huge sub was part of a group the Japanese built toward the end of World War II. The massive vessels were able to carry up to three folded wing airplanes in their holds.
Those planes would then be launched against enemies. The sub found, I-400, was meant to attack the Panama Canal.
The sub was discovered by NOAA in 2,300 feet of water just off the coast of Hawaii.
"In cases like this, when you find historic shipwrecks, what you’ve done is not just something archaeological," NOAA’s James Delgado told the New York Times.
"You have added into the catalog of the world’s greatest museum: the bottom of the seas."
The Navy intentionally used the submarine for target practice and sunk it in 1945 to keep it out of the hands of the Soviet Union. After the war an agreement was made with the USSRR that allowed them access to captured technology.
If that technology was nearly a half a mile underwater, it was safe.
So far there have been no plans made to bring the 400 foot monster to the surface.