Feeling rather like a traditional British whodunit, I suppose Behemoth, The Sea Monster (1959, aka The Giant Behemoth aka The Behemoth) is best characterized as science-detective fiction grafted onto a kaiju movie. A man and his daughter, fresh in from fishing off the Cornish coast, pull into a cove, and she runs off to start dinner. He loiters a trifle too long after she leaves, and something … gets him. Hours later, his daughter and another fisherman find him as he expires, badly burned, muttering.
Before long a marine biologist and another scientist are investigating, pawing their way through various fishy specimens, and eventually discover there’s radiation involved. Soon they use radar (for an underwater object?) to track whatever it is, but that fails. A visual search comes to a grisly ending for those involved, which was a trifle unfortunate for the redshirts manning the helicopter sent out to look manually, as they get mysteriously fried, which is even more frustrating because we lose the best character of the lot, a slightly wacko paleontologist, in the incident. The military refuses to blockade the Thames, which for reasons unclear is where our agent of malfeasance is heading, and soon it knocks over a car ferry, terrifies the locals, and then submerges again.
Soon, we’re on a monster romp through London, but the scientists devise a torpedo with a radium tip, and, enticing the Behemoth back into the Thames, manage to shoot it into Mr. B’s head. The End.
Except … there’s reports of dead fish washing up on America’s East Coast.
Right up front, I’ll say that some of the science is screwy. Radar is not used underwater, that’s where sonar excels, for example. But the plot is very much an example of scientists gathering data, analyzing it, making educated guesses, and following through. There’s some cool stuff, even, for example when they discover an irradiated fish by placing it on a glass plate sensitive to radiation, and it showing the fish’s skeleton.
Unfortunately, it’s hard to make scientific method exciting, and so the movie tends to be a bit of a plodder. When we finally do get a good look at Mr. B, it’s really a trifle disappointing, although I’ll admit the extreme closeups of his head did make me laugh. But the acting is OK, the story is good, and the monster is at least a bit temperamental about getting hit with electricity.
This doesn’t really qualify as horror, so don’t watch it expecting to curl your toes. In some ways, it’s a historical curiosity. I couldn’t possibly recommend it … but you might enjoy it if you’re of a certain turn of mind.