Kaitei Sanman Mile
Japanese title: 海底3万マイル
Type: Movie
Episodes: 1
Source: Original
Genres: Adventure, Fantasy
Studios: Toei Animation
Duration: 59 min
Rating: G - All Ages

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)