Phantom from 10,000 Leagues - 1955

A professor works for an oceanography college on the Pacific coast. He has a daughter. A series of fishermen deaths are reported. A government investigator---not the FBI---and a scientist show up. They soon discover an unexplained source of atomic power on the ocean floor that is guarded by a strange monster. The scientist learns from the professor's secretary that his experiments have something to do with the strange monster. The agent learns that negotiations to sell the atomic inventions, and the very strange monster, to a foreign power are underway. The secretary is killed by the professor's assistant, who has been seeking to turn over the atomic-secrets to a foreign power. The agent discovers the assistant's activities and arrests the assistant and the foreign agent. A ship explodes off the coast. The professor now---just now?--realizes that the undersea weapon and the strange monster are a danger to humanity. The professor dives into the sea with intent to blow up the weapon with dynamite. The monster grabs him and the professor, the strange monster and the atomic weapon are all blown up. Finis.