Trivia

The villain's submarine was modified from a Space: 1999 (1975) Eagle play-set. The toy was made by Mattel in 1976, two years before the film. The engine section, side cargo doors, command capsule and framework superstructure from the Eagle are all visible on the modified submarine.

The model submarine Nautilus used in filming was originally built as one of the "Seaview" filming models (eight feet long) for Voyage to the Bottom of the Sea (1961), also created/written/directed/produced by Irwin Allen. Many Hollywood prop collectors bemoaned the conversion of the Seaview for use in this very short-lived TV show.

The movie is in three parts whose on-screen titles are: "Deadly Blackmail" (Pt1); "Duel in the Deep" (Pt2); and "Atlantis Dead Ahead" (Pt3).

This film is a compilation of a 3-part TV miniseries that aired March 8, 15 and 22 in 1978. The three episodes were titled "Deadly Blackmail", "Duel in the Deep" and "Atlantis Dead Ahead". It was intended to be the launch of a new series in the same vein as its 1964 to 1968 predecessor, Voyage to the Bottom of the Sea. The ratings were so dismal that the hoped-for series was never ordered. It did win a couple of Emmy nominations for optical effects and special photographic effects.

The Pit's dive of Submarine Nautilus is older on riveted plates as usually in 19th century, however the same pit's dive appears on modern Prof. Waldo submarine where this obsolete technology was already replaced by welding plates.