Kaitei Daisensou: Ai no 20,000 Miles (1981)
https://nyaa.si/view/1886837 Fansub credits can be found in the link above. This is an English fansub of a 1981 TV special by Tatsunoko Productions, titled Kaitei Daisensou —taking place in a world where the evil Gabia empire (controlled by Emperor Darius) has taken over most of the planet Earth, undersea explorers Ricky and Ben dedicate themselves to searching for ancient underwater civilizations when they are suddenly picked up by the mysterious Captain Nemo and his submarine, the Nautilus. Things begin to get tense when Emperor Darius eventually starts chasing after the Nautilus, as he firmly believes he can't be a complete ruler unless he gets rid of Captain Nemo... Many, many years ago, GANGO translated this into English after I managed to snag a low-quality raw from a (now dead) torrent. A while back, I found out that this got added onto JP streaming services, utilizing a slightly better video source than that of the original JP VHS. And so, perevodildo and I partnered up tog