'The Great War of the Monsters')[1] is a 1965 kaiju film directed by Ishirō Honda, with special effects by Eiji Tsuburaya.

It was followed by a theatrical release in the United States on July 29, 1970, by Maron Films as Monster Zero, on a double bill with The War of the Gargantuas.

[13] In the year 196X,[4] two astronauts, Fuji and Glenn, are sent to investigate the surface of the mysterious "Planet X" recently detected on the far side of Jupiter.

The monster eventually leaves, but the Controller states that Ghidorah has been attacking repeatedly, forcing them to live underground in constant fear.

The tape is played for the world's leaders, but instead, it contains an ultimatum demanding that they surrender Earth to the Xiliens or be destroyed by Godzilla, Rodan, and Ghidorah, who are all under the aliens' mental control.

The invasion is thwarted and the Xiliens, unable to fight back or retreat, destroy themselves en masse.

All three topple off a cliff into the ocean; Ghidorah surfaces and flies back into outer space, while those watching speculate that Godzilla and Rodan are probably still alive.

[17] Saperstein approached Toho and began involvement in the film when Frankenstein Conquers the World was already in its production phases.

[20] This role was eventually filled by Nick Adams, who had previously starred in Frankenstein Conquers the World without any suggestion from Saperstein.

This led to special effects scenes having less elaborate model cities built and including footage which had been shot for previous films such as Rodan, Mothra, and Ghidorah, the Three-Headed Monster.

[23] Yoshio Tsuchiya improvised the Planet X Controller's hand gestures and combined French, German, and Ryunosuke Akutagawa's Kappa language to form the alien dialect, at Honda's request.

[23] The Godzilla Shie victory dance was added after Yoshio Tsuchiya suggested it to Tsuburaya, who was already supportive about anthropomorphizing monster characters with comical traits.

[27] Godzilla performer Haruo Nakajima, effects cinematographer Sadamasa Arikawa, and director Ishirō Honda were against the inclusion of the dance.

[30] In one scene, the effects crew wanted to show the 3-meter P1 lift from a low angle, however, its size would have exposed the top edge of the Planet X set.

[31] Against company policy, special effects art director Yasuyuki Inoue broke the sound stage floor, and dug a hole to allow the P1 to rise from the subterranean base.

[34] Effects animator Sadao Iizuka created the transport tractor beam and designed it after a Neon club sign he saw in Shibuya ward.

The new suit removed the kneecaps from the previous two film, the breast bone is slightly retained and deemphasized, the dorsal fins are less pointed, and the eyes are enlarged.

[38] For Ghidorah, the suit was repainted with a darker shade of gold, with fewer details on the faces due to settled rubber.

[5] It was re-issued in Japan in 1971 where it was edited to a 74-minute running time under the title The Giant Monster War: King Ghidorah vs. Godzilla (怪獣大戦争 キングギドラ対ゴジラ, Kaijū Daisensō Kingu Gidora tai Gojira).

[47] Co-producer Henry G. Saperstein commissioned an English dub from Glen Glenn Sound, a Los Angeles-based company, for the film's American release.

[17] Among the changes in the American version of the film include improvised "Planet X language" scenes spoken by Yoshio Tsuchiya being cut, and a few brief shots involving the flying saucers at Lake Myojin.

The audio was changed as well with sound effects added for Godzilla and several pieces of Akira Ifukube's score re-arranged.

[10] The English dialogue was written by an uncredited Riley Jackson, who was hired by UPA post-production supervisor S. Richard Krown because of his previous work on Storm Over the Pacific.

[26] Originally released as Invasion of the Astros at military bases in the United States,[51][52] the English dub by Glen Glenn Sound was released on July 29, 1970, by Maron Films[3] as part of a double feature with The War of the Gargantuas (also dubbed by Glen Glenn Sound).

Variety reported again in September 1970 that both the film and The War of the Gargantuas "sat on the shelf at [UPA] because [distributors] figured they had no potential".

"[54] The presentation for the Criterion Channel states: "This retro romp, featuring American star Nick Adams, stands as a high point in the Showa Godzilla series.