Kaitei Sanman Mile
Genres: Adventure, Fantasy
Type: Movie, Episodes: 1
Aired: Jul 19, 1970
Studio: Toei Animation
Source: Original
Rating: G - All Ages
Synopsis:
Returning home from an ocean trip, young Isamu meets the beautiful sea-dweller Angel on a volcanic island. Attacked by a fiery dragon, Isamu and Angel escape on the observation boat See Through, and Angel invites Isamu to see her undersea kingdom of Atlas.

(Source: AniDB)