Atragon

The legendary empire of Mu reappears to threaten the world with domination. An isolated World War II Captain has created the greatest warship ever seen and possibly the surface world's only defense, a submarine named Gotengo. While countries unite to resist, Makoto Jinguji, daughter of deceased Imperial Captain Jinguji, is pursued by a suspicious character who claims to be an agent of the drowned Mu Empire. A package inscribed "MU" arrives for Admiral Kosumi, demanding that he appeal to Jinguji and foiling his plans.