Eugène Lourié later acquired a 35mm print of the movie for private use and cut out all the stock footage military shots.
First film of Harvey Hall.
Scenes in which the baby Gorgo is driven through London were shot on a Sunday morning, which meant hardly anyone was in the streets. This was then explained away by a "TV announcer" who said that people were told to stay indoors.
The concept for the British poster art and lobby cards was that the face of Gorgo was not revealed. The idea is based on the line of dialogue in the film from Martin Benson, that Gorgo's name is derived from the Gorgon sisters of Greek mythology. The sight of their faces would turn you to stone.
The ending was inspired by Eugène Lourié's daughter who cried at the end of the The Giant Behemoth when the monster was killed. When this happened, he decided to let both monsters live.
The film had its London Premiere on 27 October 1961 at the London Pavilion, the theater seen in the scene where Gorgo is being driven through Piccadilly Circus, and was double-billed with My World Dies Screaming. It went on its suburban London release on the ABC circuit on 27 November 1961.
The film was originally set in Japan. Later, the King Brothers and Eugène Lourié thought of setting it in Paris, but that would have meant the monster would have had to wade about 100 miles up the Seine to get to the city. Finally, the location was changed to Ireland and England.
The original script had no military action indicated. Director Eugène Lourié argued that gunfire would kill a beast, no matter how big. The King Brothers wanted guns and they got them.
When Gorgo is being driven through Piccadilly Circus the West End cinema London Pavilion is showing the Hammer version of The Mummy.