Loosely based on "The Incredible Tide" by Alexander Key. The basic premise is same, but the story in the anime is mostly Hayao Miyazaki's original. In the book, Conan is 14, while in the anime he is 11. Conan doesn't have superhuman strength in the book, as he does in the anime. Miyazaki said he didn't like the book very much. When the project was brought to him, he made sure that he could change the story however he wanted.
First animated series to air on Japanese Public TV, NHK.
Unlike many other anime shows from that time period, this one was never picked up by a German TV station for broadcast and so was mostly unknown. Only in 2022, polyband Medien started a crowdfunding campaign on Kickstarter for an official German release. That campaign was successful and a Blu-ray/DVD release is scheduled for 2023.