The film was released theatrically in the United States in the summer of 1970 by Maron Films as Monster Zero, where it played nationwide on a double bill with War of the Gargantuas.
In the late 1960s, a two-man spacecraft with a Japanese and an American crew (Fuji and Glenn), approaches Jupiter's orbit to explore the newly discovered Planet X; a planet that maintains a position directly behind Jupiter, leaving its surface in twilight, with just enough light to make it possible to navigate its surface.
After landing and disembarking, one of the astronauts and the ship vanishes, leaving the other to wonder where they have gone. Suddenly, a flat voice comes over the communications link and instructs the lone astronaut down into subterranean corridors to the office of the Controller of Planet X, where he finds his shipmate.
The spacecraft is safe, the controller assures them and indicates that their location is about to be attacked. The astronauts recognize the attacking monster is King Ghidorah, the three-headed space dragon. The astronauts lose contact with the Controller, but afterwards they are assured that Ghidorah, known to the Xians as Monster Zero, is gone.
The Controller asks for Earth's help: they want to capture Godzilla and Rodan, known to the Xians as Monster Zero-One and Monster Zero-Two. In return, Planet X will gift humanity with a wonder drug that can cure all diseases. The astronauts agree to return home with the proposal. As they lift off, they say on the radio to the Controller, "We're glad we found friends on Planet X."
Meanwhile, Fuji's sister's boyfriend, Tetsuo, has invented a personal alarm he thinks women could use if they're attacked. It creates an extremely loud noise that can be heard for a long distance. Tetsuo wonders, though, why no one is interested in buying it. Eventually, a Miss Namikawa makes an offer to buy the alarm as an educational device, although she continually hesitates to complete the deal. In truth, her boss wants the device and the plans destroyed.
Glenn, Fuji and Dr. Sakurai are invited to accompany the Controller back to Planet X, a trip that takes only a few hours; the Controller says that soon they'll be able to travel at the speed of light. When they reach Planet X, there is an immediate attack by Ghidorah, and the two monsters from Earth are released to battle him. Ghidorah is driven off and the Controller is extremely happy. He presents the astronauts with a box he says contains the formula for the miracle drug. He also gives the three men duplicate of their spaceship so they can fly home.
The Xians soon arrive and destroy the gift spacecraft. They also threaten to release King Ghidorah, Godzilla and Rodan. Overly confident, the Xians show the world how they control the monsters through magnetic waves. The Earth scientists know they can exploit this information and work rapidly to find a way to disrupt the waves. Meanwhile, Earth's armies fight the three monsters with conventional weapons as they destroy much of Japan.
They reach the space center scientists and explain about the alarm. Arrangements are made to broadcast it on all radio and television stations, but only when the magnetic disruption devices are deployed.
Glenn and Fuji are to be sent to Planet X again as ambassadors to seek peaceful relations.
- Nick Adams as Glenn
- Akira Takarada as Fuji
- Kumi Mizuno as Namikawa
- Jun Tazaki as Dr. Sakurai
- Akira Kubo as Tetsuo Torii
- Keiko Sawai as Haruno Fuji
- Yoshio Tsuchiya as Controller of Planet X
During the scenes where Godzilla & Rodan are attacking, stock footage from the original Rodan is used, specifically from the scene where Rodan blows over a train and the scene where two soldiers are blown away.
The film was released in North America by UPA in 1970 under the title Monster Zero. It played on a double bill with War of the Gargantuas.
There were several alterations made:
The opening theme was changed, and some of Akira Ifukube's score was re-arranged. Several sound effects were also added.
Deleted: Several shots of Godzilla's foot stepping on houses and huts. Some short shots of flying saucers. Rodan blowing away tanks from the top of a hill. Several scenes with the Xians speaking in the language of Planet X.
The scene where Godzilla does his dance has added stomping noises in the English version.
The English version runs 93 minutes, three minutes shorter than the Japanese version. In his book Japan's Favorite Mon-Star: An Unauthorized History of 'The Big G', Steve Ryfle says "The Americanization...is respectful to the original Japanese version."
Also, in the original Japanese version of the film, the drug the Xians promised was a cure for all forms of cancer. However, in the English version of the film, the cure was for all forms of disease (perhaps due to a translation mistake).
During production, Nick Adams spoke his lines in English, while the Japanese actors spoke their lines in Japanese, in order to retain his voice for the English-language version. For the Japanese language release, Adams' was dubbed by the noted voice actor, Goro Naya. The English-language version was prepared by UPA at Glen Glenn Sound in Hollywood, and Marvin Miller provided the English voice for Akira Takarada as Astronaut Fuji. The remaining voice talent is unknown.
The Great Monster War - Translated Japanese title.
Invasion of Astro-Monster - Toho's official English title and current home video title.
Monster Zero - Original US title.
The Great Monster War - King Ghidorah vs. Godzilla - Japanese 1971 Champion Festival reissue title.
Invasion of the Astro Monsters - UK home video title.
Godzilla vs. Monster Zero - Previous home video and TV title.
In Japan, the film sold approximately 3,780,000 tickets.
Release date: June 5, 2007
Special features: Audio Commentary by Stuart Galbrath IV, Tomoyuki Tanaka biography, and original trailer.
Note: Contains both original Japanese and English versions of the film.
Note: Part of the Toho Collection