Loosely based on "The Incredible Tide" by Alexander Key. It is rather difficult to find this book today. The basic premise is same, but the story in the anime is mostly Miyazaki's original. In the book, Conan is 14 (in the anime he is 11), and doesn't have superhuman strength like Conan in the anime does. 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.