Godzilla vs. Megalon

Godzilla vs. Megalon , Gojira tai Megaro? is a 1973 Japanese science fiction kaiju film produced by Toho. Directed and cowritten by Jun Fukuda with special effects by Teruyoshi Nakano, the film starred Katsuhiko Sasaki, Hiroyuki Kawase, Yutaka Hayashi, and American actor Robert Dunham. It was the thirteenth film in the Godzilla franchise. Heavily influenced by the tokusatsu superhero TV shows of the time, the film had Godzilla essentially acting as a costar to a huge robotic superhero character called Jet Jaguar.

In the year 1973, the most recent underground nuclear test, set off near the Aleutians, sends shockwaves as far south as Monster Island, disturbing the monsters, causing Anguirus to fall into a fault opened up by the consequential earthquakes and Rodan to fly off, while Godzilla decides to stay put.For years, Seatopia, an undersea civilization, has been heavily affected by this nuclear testing conducted by the surface nations of the world. Upset by these tests, the Seatopians plan to unleash their civilizations beetlelike god, Megalon, to destroy the surface world out of vengeance. ........

Source: Wikipedia