After years of being dubbed, Akira Takarada and Akihiko Hirata are heard using their own voices to speak English in this film.
When the television syndication contracts had expired this film became unavailable, reportedly due to a dispute over the rights.
Lucretia, the evil Malic's companion, was played by 'Patricia Medina'. At the time this was filmed, she was married to Joseph Cotten who was playing good guy Captain Craig McKenzie.
Although this was only special effects director Eiji Tsuburaya's next-to-last film, it was also not only his last sci-fi/fantasy film, but the last time he would work with director Ishirô Honda, with whom he worked on many of Toho's classic tokusatsu movies, including the Godzilla series.
His screenplay, based on his original stories, would be the last work in the film industry for Ted Sherdeman, ending a career in motion pictures that lasted about 20 years.
Linda Haynes celebrated her 21st birthday while acting in this film.
The character Perry Lawton brought back 600 carats (just over 1/4 pound) of diamonds from the underwater city. Even if all the diamonds were industrial grade, this was a great fortune.