Japan's Self-Defense Forces gave assistance to this production and allowed the filming of military equipment and personnel. Through them, the production was also allowed to shoot TôhôScope-wide footage, especially of military aircraft, at United States Military installations in Japan.
There are in fact two runs of The Mysterians. The original dub was released by RKO/MGM in 1959, and corresponded to the 3 minutes of edits in the American cut. This dub was released on VHS a few times, panned and scanned with warbly sound. For the DVD release, Media Blasters created a new dub which corresponds to the Japanese cut. This dub is generally regarded by the fandom as poorer, and is responsible for the goof mentioned in the Goof section, wherein it's mentioned that one of the firefighters has a Southern accent. This is an error only present in the DVD dub
An early concept of Mogera was of a four-footed mecha, more along the lines of a mole. The name Mogera was based on the Japanese word for mole ("mogura"), which was not in the original script, but was added at the insistence of producer Tomoyuki Tanaka, who felt the movie needed a giant monster.
U.S. press material issued at the time of the film's original release incorrectly listed Masaru Satô (another highly regarded Japanese film composer), rather than Akira Ifukube, as the creator of the score.
This was one of the first Japanese productions to be shot in anamorphic widescreen. Tôhô Kabushiki Kaisha, which called its anamorphic process TôhôScope, specifically made this film to show off the new process. Part of Akira Ifukube's battle score was used on the TôhôScope logo, which appeared at the beginning of the Japanese-language prints.
Mogera, the giant robot that was added to the film, was created to be a Godzilla-like mechanical monster, including spines along the back and a large tail. In the final edit of the film, most of the selected shots hide the fact that the robot does have a tail.
In the original Japanese-language version, the aliens are called Mysterians (rendered in katakana as Misuterian). When he visited the United States, special-effects director Eiji Tsuburaya was surprised to discover that the term Mysterians was well-known. It had also been used in the English-language dubbing, and the film had even been released in the United States under the title "The Mysterians."
The one-hit-wonder band Question Mark and the Mysterians named itself after the the movie's US title, "The Mysterians." The band is known for the song "96 Tears" and the eccentric behavior of its leader, who had his name legally changed to an actual question mark.
The Mogera suit, originally worn by Haruo Nakajima, was, after filming, kept in storage in one of Tôhô's visual effects soundstages until 1974, when it was destroyed in a fire on the lot, caused by a pyrotechnical accident during the filming of Nosutoradamusu no daiyogen (1974).
When Metro-Goldwyn-Mayer took over the first-run distribution from RKO in the United States, it packaged it as a double feature with the bottom feature being the British-made negative pickup First Man Into Space (1959).
The USA premiere of the Mysterians, Aka Chikyû Bôeigun (tôhô, 1957) was on October 30, 1958, at the United Artists Theater in downtown Inglewood, California. A giant 6-foot-tall cardboard standee poster of Mogera was placed outside of the theater, facing the street. It was released by RKO and Warner Bros. for that release, then MGM re-released it again in May 1959. It is available on VHS, Laserdisc from Tôhô, and on DVD from Tokyo Shock, 2005. The reissue DVD has a re-recorded English-language soundtrack with new voice actors and is not the original 1958 USA release soundtrack that had Paul Frees as the voice of actor Takashi Shimura, who played the veteran scientist Dr. Tanjiro Adachi, as he also did for this actor in voiceover work in Godzilla: King of the Monsters (1956) and Mosura (mothra) (1961).
When Toho was only allowed one hour to film footage of the Military Air Transport Service cargo plane unloading, producers shut down production of the film and used all available cameras to shoot the operation from different angles. By hiding the plane number, it appears that multiple planes have landed. Toho did a similar thing in "Gojira/Godzilla." Only allowed to film the movement of one military convoy, producers simply put their cameras in jeeps and raced ahead of each section of the convoy to make it seem as if the convoy was massive.
The trivia item below may give away important plot points.
At the end of the English-language US version, the last Mysterian saucer is seen ascending into the upper atmosphere. In the original Japanese-language version, this is revealed, through dialog, to actually be an Earth satellite that is launched to monitor the Mysterians and prevent a future attack.