Behemoth, the Sea Monster

The Giant Behemoth aka Behemoth, the Sea Monster and The Behemoth is a 1959 AmericanBritish science fiction giant monster film coproduction. Originally a story about an amorphous blob of radiation, the script was changed at the distributors insistence to a pastiche of The Beast from 20,000 Fathoms 1953, though elements of the original concept remain in the early parts of the film and in the nuclearbreathing power of the titular monster.

A man, his son, and their dog are the next victims of the creature. A photo of the area reveals a huge footprint of some prehistoric animal. Dr. Sampson Jack MacGowran, a paleontologist, identifies the creature as a Paleosaurus, an aquatic dinosaur that emits an electric pulse, like an eel. Karnes believes that the dinosaur is saturated by radiation, which is transmitted by the electric pulse, resulting in the burns that killed the fishermen and other victims. The radiation is also slowly killing the dinosaur. According to Dr. Samson, the dying creature will leave the ocean deeps to head up stream, seeking out the shallow waters where it was born unfortunately death by radiation may not come soon enough to prevent the creature from wreaking havoc on London along the way.Karnes and Bickford try to persuade authorities to close the Thames, but the military believes their radar tracking systems will be enough to detect the behemoth and prevent it from getting near the city. Unfortunately, the dinosaur appears to be invisible to radar. Dr. Sampson and some other scientists spot it from a Royal Navy helicopter, but the radar equipment tracking the helicopter sees no sign of the beast, which destroys the helicopter with its radioactive emanations. Soon, the Behemoth surfaces in The Thames and destroys The Woolwich Ferry by capsizing it. ........

Source: Wikipedia