Ebirah, Horror of the Deep (movie, 1966)

Searching for his brother, Ryota stows away on a boat belonging to a criminal alongside two other teenagers. After being caught in a storm the group arrives on Letchi island, where the Infant Island natives have been enslaved by a terrorist organization and held captive by a crustacean monster. Discovering a sleeping Godzilla, they decide to wake him up to defeat the terrorists and liberate the natives.