Many of the invasion scenes in Tokyo were edited from an earlier Toei tokusatsu epic, La guerra final (1960). The appearance of a giant billboard of Adolf Hitler has led some viewers to believe that the stock footage is taken from documentary footage of World War II Japan, which it wasn't. The billboard of Hitler is actually an advertisement for a Japanese translation of Mein Kampf.
This film was released in its native Japan on July 19, 1961. In the United States, the film was not released theatrically, but was released directly to television by Walter Manley in 1964 (with several edits).
This film has the third Toei Superhero role for a young Shin'ichi Chiba, here in an early film role, who previously played the title superheroes in the Toei TV series Nana-iro kamen (1959) (which was also his acting debut) and Arâ no shisha (1960). Here, he plays Shinichi Tachibana, a mild-mannered young scientist who is secretly a caped/masked marvel, Iron-Sharp (named by the children protagonists in this film), who travels in the flying supercar of the film's title, the Space Greyhound, which can also shoot lasers. (The car is actually a modified miniature sports car.) Iron-Sharp is called Space Chief in the US version.
Famed artist and veteran designer Tôru Narita, who designed this film's costumes and spaceships, would later become more famous for designing the titular superheroes of Tsuburaya Productions' Urutoraman: Kûsô tokusatsu shirîzu (1966), Ultrasiete (1967), and the two eponymous monsters in Toho's La guerra de los gargantúas (1966). Shortly before this film, Narita was the art director on another Toei Superhero production, the TV series National Kid (1960).
A walking toy of Robby the Robot, the famous robot character from the sci-fi classic film El planeta desconocido (1956), makes an appearance when this film's children protagonists test a metal detector rod on it. It can also be argued that the look of the Neptune henchmen may have been inspired by Robby, with dome like helmets and rotating circular antennas. (Instead of the antennas, the Neptune Men's leader has a transparent disc around the top of his helmet.)