One of the earliest Japanese cartoons to come to the US, Marine Boy is now available from Warner Archive in a three-disc, 26-episode first season set.
It was produced beginning in 1965 and aimed at the English-speaking syndication market. (I recall seeing this in the mid 1970s in England and then wanting to pretend to be Marine Boy and his mermaid girlfriend on the playground.)
The story is basic but attention-capturing. Marine Boy is an invention-enhanced teenager who works with the Ocean Patrol to fight bad guys. His father is a scientist, and he has a dolphin, Splasher, for a pet and companion. Oxy-gum made it possible for him to breathe underwater.
There’s also a young mermaid, Neptina. Both she and Marine Boy were voiced in English by Corinne Orr, voice of Trixie on Speed Racer, while dad was Peter Fernandez, Speed Racer himself. Both series were narrated by Jack Curtis.
I haven’t seen the remasters yet, but I’m guessing that, while it may look a little simple compared to today’s anime, it’ll still fire kids’ imaginations.