For many years it was widely believed that the failure of the original copyright holder to renew the film's copyright had resulted in it falling into public domain, meaning that virtually anyone could duplicate and sell a VHS/DVD copy of the film. Therefore, many of the versions of this film available on the market were either severely (and usually badly) edited and/or of extremely poor quality, having been duped from second- or third-generation (or more) 16mm pan/scan television copies of the film purchased on the underground market. The legal status of the film was eventually resolved by 20th Century-Fox, and the movie was rescued from public domain so that a quality DVD could be released through Fox Cinema Archives. Fans are now able to enjoy the movie with stereo sound and a quality picture--complete with the "lost" scene in which Gilbert Roland stuffs a cigar into Peter Graves' mouth after beating him in a fistfight.

Filmed in Tarpon Springs, FL. As of 2019 is it still the home of the natural sponge industry in the US, and has the highest percentage of Greek-Americans of any city in the country.

Underwater sequences were filmed with a French specialty camera named the Aquaflex.

Robert Wagner was nearly drowned during filming at Tarpon Springs, FL, when he was kicked in the abdomen by another swimmer. He sank to the bottom and had to be rescued by a crew member.

Third film to be shot in CinemaScope, following The Robe (1953) and How to Marry a Millionaire (1953).

Kathleen Crowley and Debra Paget were considered for the female lead that went to Terry Moore.

Famous puppeteer Jack Shafton made the miniature figures used in underwater sequences.