Richard Briers has claimed in interviews that he finds the plot of this film hard to fathom
Exotic Spanish locations in the region of Andalucía seen in the film included Málaga, Nerja, Mijas and Torremolinos.
Fathom's name was an amalgam of the first names of the character's uncles who were called (in order of the letters in Fathom's name) Freddie, Arthur, Tom, Harry, Oscar and Milton.
H.A.D.E.S stood for Headquarters Allied Defences, Espionage & Security.
The name of this movie's MacGuffin was the Fire Dragon. At first, it is described as a failsafe device that can explode a hydrogen bomb via an electronic signal but turns out later to be a a priceless Oriental ceramic treasure from the Ming Dynasty.
The opening title sequence was designed by Maurice Binder who regularly did the opening titles for the James Bond movies from the 1960s right up until the late 1980s.
This 1960s spy comedy is bookended by aerial plane, parachuting and skydiving sequences. This movie was influenced by the James Bond franchise, and ironically, such above-mentioned aerial activities would actually make this picture prefigure the many aerial and flying stunt sequences which would dominate the Bond series from the 1970s onwards.
This movie was based on Larry Forrester's second 'Fathom' novel which was never published and was only in draft form at the time of production and release. Forrester's first 'Fathom' novel was called 'A Girl Called Fathom' and was first published in the same year as this film was released: 1967.
This movie was one of three 20th Century Fox pictures featuring female spies that were released in 1967. The other movies were Come Spy with Me and Caprice. The studio was also responsible for the comic book female spy flick Modesty Blaise released the previous year.
This spy spoof movie, influenced by the James Bond film franchise, features actor Tom Adams in a supporting role as Mike, the Owner of Casa Miguel. Adams actually played a James Bond knock-off character Charles Vine in three movies during the 1960s era in which this movie was made. The films were The Second Best Secret Agent in the Whole Wide World, Where the Bullets Fly and O.K. Yevtushenko.