Why all the dubbing?
As the notes on this site reveal, star Todd Armstrong's voice was dubbed by Tim Turner, and female lead Nancy Kovack's voice was dubbed by Eva Haddon.
I believe that another case of dubbing in the movie is the voice of the figurehead-Hera: I believe Joan Greenwood (who'd been one of the stars of the Ray Harryhausen movie released two years before this one, Mysterious Island) spoke some of those lines. (I'm very familiar with Honor Blackman's voice from her work in The Avengers, Goldfinger, and several television roles--and because of this familiarity, I am fairly certain that it was not she reading some of wooden-Hera's line. However, this is just an opinion; I have no proof).
At any rate, I'm curious as to the reason for dubbing the two leads (as well as possibly other performers). I did some searching but can't find a discussion of the topic.
Both Todd Armstrong and Nancy Kovack, though certainly not household names, were working actors with respectable credits--so it's not as if their own voices would have been unacceptable to audiences.
Was it common with "B" movies filmed overseas, to film the performers but refrain from paying them to come to the studio and loop their dialogue? That's my best guess at the moment.
Anyone have any better information on this?