powered by AFI
The end credits contain the following written statement: "We gratefully acknowledge the cooperation of the Ground Observer Corps." The film begins with a lengthy voice-over narration describing the radar "fences" throughout North America that serve as a distant warning system for the American and Canadian military. The construction of the farthest radar system, known as the Dew Line, is shown, using archival footage. A similar voice-over later describes CONAD and the radar it uses as "the shield that could mean the difference between life and death for all Americans." According to a May 1956 Hollywood Reporter news item, Universal originally considered Mara Corday and Rex Reason to co-star in the film.
Studio press materials reveal the following details about the creation of the film's special effects: One papier-mach model of the mantis was built for the picture, measuring 200 feet long and 40 feet high, with a wingspan of 150 feet. It was fitted with a hydraulic system to raise its legs. Two smaller models, one six feet long and the other one foot long, were also constructed for use in walking and flying scenes. For the scene in which the bug climbs the Washington Monument, close-up shots of a real mantis were used. According to modern sources, the footage of an Eskimo village included in the film was taken from the 1933 Universal film S.O.S Iceberg, which was directed by Tay Garnett and starred Rod LaRoque (see AFI Catalog of Feature Films, 1931-40). Modern sources also identify some stock footage used in the film as being drawn from Air Force short films, including Guardians All, One Plane-One Bond and SFP308.