Kaitei Daisensou: Ai no 20,000 Miles

All the nations of Earth are crumbling before the might of Darius, ruler of the Gabia Empire. Meanwhile, childhood friends Ben and Ricky are sailing on the oceans is search of the lost city of Atlantis. When their ship is sunk they are saved by Captain Nemo in his submarine Nautilus.
(Source: Anime News Network)