South Dakota was a full generation more advanced then Nagato. Even the most modern Battleships were obsolescent in the Post War World. What is this fleet you think the Japanese had in their shipyards. They had some carriers, destroyers, and submarines. The carriers were obsolescent in the jet age, and would need major rebuilds like the American Essex Class did. The destroyers were good ships, but their armament, and fire control, accept for torpedoes needed to be completely replaced. The submarines, accept for the I-201 class were outdated junk.