This was the only film in the original Gamera series to be released to American theaters. It was originally presented in America by World Entertainment Corp. and Harris Associates, Inc. who re-named the film Gammera the Invincible. All subsequent entries in the series were released directly to television by American International Productions Television. Gammera the Invincible's American premiere was in New Orleans on December 15, 1966. Gammera the Invincible was heavily re-edited from its original Japanese version. Scenes were moved around and some were deleted completely. New footage featuring American actors was spliced in to create a more international feel and to replace scenes shot in the original cut featuring American extras with poor acting. Theses new scenes featured actors such as Albert Dekker and Brian Donlevy. The film was dubbed by Titan Productions, Inc. It features the voices of Jack Curtis and Peter Fernandez, who are best known as voices on Speed Racer and Ultraman. The film opens with Gamera's awakening from the accidental detonation of an atomic bomb as a result of an aerial assault by American fighters on Soviet bombers caught crossing into North American airspace. Gamera wastes no time in causing a rampage of destruction, first destroying a Japanese research ship, then making its way to Japan to wreak havoc. In an attempt to stop the giant turtle, Gamera is sedated with a freezing agent on a precipice, and powerful explosives are placed at the base. The explosion knocks the monster on its back, and while it seems as though mankind has scored a victory, this is not the case: Gamera reveals its ability to fly. A second strategy, Plan Z, is devised to stop the monster, this time by baiting it into a rocket bound for Mars. The plan is successful and the Earth is safe from Gamera.