Yoinked from the almighty wikipedia monster ...
"Ebirah, Horror of the Deep, (released in Japan as Godzilla, Ebirah, Mothra: Big Duel in the South Seas (ゴジラ・エビラ・モスラ 南海の大決闘 Gojira, Ebira, Mosura Nankai no Daikettō) is a 1966 Japanese science fiction kaiju film produced by Toho. Directed by Jun Fukuda with special effects by Sadamasa Arikawa (supervised by Eiji Tsuburaya), the film starred Akira Takarada, Akihiko Hirata, and Eisei Amamoto. The 7th film in the Godzilla series, this was the first of two island themed adventure films starring Godzilla.
The film was originally written for King Kong (the project was tentatively titled Operation Robinson Crusoe:King Kong vs Ebirah), but Toho switched Kong with another popular character at the time, Godzilla. This explains why Godzilla displays uncharacteristic behavior in the film, such as drawing strength from electricity, his curiosity to Kumi Mizuno's character, the usage of boulders to destroy the Red Bamboo Base, and his hostilities with Mothra (despite them now being allies). Toho would later use Kong for King Kong Escapes.
The US television version and early video versions have a different opening to the film. The opening scenes of Ryota at the Maritime Safety Agency searching for news of his brother have been replaced with a scene supposedly showing Ebirah destroying Yata's boat. This sequence was created by editing a later scene in the movie. The current DVD version of the film restores the Japanese cut.
In 1991, Godzilla vs. the Sea Monster was distributed under the Film Ventures International name. The company replaced the opening with a generic credit sequence, using footage from Son of Godzilla. This version was aired on Mystery Science Theater 3000."