They find the remains of an advanced submarine sunk by the U.S. Navy in 1946 . The submarine was essentially an underwater aircraft carrier . The Soviet Navy wanted to exploit the submarine 's advanced technology . The submarine represented a big shift in submarine tactics , a researcher says .
Researchers find the remains of an advanced submarine sunk by the U.S. Navy in 1946 . The I-400 was essentially an underwater aircraft carrier . The Soviet Union wanted to inspect the sub 's advanced technology . The sub represented a big shift in submarine tactics , a researcher says .