The "Phantom" is a man-sized reptilian creature mutated by a radioactive rock. It was unintentionally created by Professor King during his experiments with a "death ray" powered by underwater uranium.
While the monster terrorizes the cove, a ring of foreign spies, including the femme fatale Wanda (Helene Stanton), attempts to steal Professor King’s scientific research. The Phantom from 10000 Leagues (1955) - Moria Reviews
The 1955 science fiction horror film is a low-budget "B-movie" produced by the American Releasing Corporation (the predecessor to AIP ). It is known for its blend of atomic-era monster tropes and an espionage-themed subplot. Plot and Characters
Marine biologist Dr. Ted Stevens (Kent Taylor) and government agent Bill Grant (Rodney Bell) investigate a series of mysterious deaths off the California coast characterized by radiation burns.