A pool was set up on stage nine during the production (stage nine is one of the largest on Toho's lot in Setagaya). They used the pool, which was about five feet deep, to film the shot of Godzilla rising above the surface of the ocean. Haruo Nakajima (the actor in Godzilla suit for the water scenes) was on a cart on a rail. He held onto the handle of the cart while it was towed by a truck. As the cart moved forward, he slowly rose out of the water. He wore a very tiny air cylinder that contained enough air for about ten minutes. The water that rushed by his face while the cart was being towed made it very difficult for him to prevent the mouthpiece from coming out of his mouth.
The name Minira started out as an inside joke short for "Mini-Gojira", because the film crew saw him as a "miniature Gojira". For the English dub, the name was translated to Minilla, meaning "Mini-Godzilla".
While the character of Minilla is divisive among the western American fandom, in Japan the character is very popular and well liked. The character routinely tops Japanese popularity polls with one fan poll ranking Minilla as the 4th most popular Godzilla monster, beating American favorites such as Mechagodzilla and Anguirus.
Upon its released on home video in Italy during the 70s, the movie was presented as a sequel to the British monster movie Gorgo (1961), with even the title being changed to "Il ritorno di Gorgo" (The Return of Gorgo). The Japanese actors' names were inexplicably changed to "John Wembley", "Keny Sahara", "Dick Kennedy" and "Charles Simon", and the directorial credit was given to Ishirô Honda instead of Jun Fukuda.
While screenwriter Shin'ichi Sekizawa had originally enjoyed writing for the Godzilla series, his irreverent approach having a major impact on the series, he nonetheless desired to do other projects and complained to Toho that he had run out of ideas for further monster movies. Director Jun Fukuda heartily agreed. Producer Tomoyuki Tanaka then proposed the idea of introducing a son to Godzilla. Toho's refusal to let Sekizawa work on other projects eventually led the screenwriter to disobey his contract and write an animated film for rival Toei studios.