The Giant Behemoth (a.k.a. Behemoth, the Sea Monster and The Behemoth) is a 1959 American-British black-and-white science fiction giant monster film distributed by Allied Artists Pictures. The film was produced by Ted Lloyd, directed by Eugène Lourié, and stars Gene Evans and André Morell. The screenplay was written by blacklisted author Daniel James (under the name "Daniel Hyatt") with director Lourié.
Originally a story about an amorphous blob of radiation, the script was changed at the distributor's 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 "nuclear-breathing" power of the titular monster.
The radiation is also slowly killing the dinosaur. According to Dr. Samson, the dying creature will leave the ocean depths to head upstream, 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 River 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.
Rising from the river, the creature attacks the city, flattens several cars and knocks a building over onto fleeing citizens. Bickford and Karnes advise the military on how to destroy the beast: bombs are out of the question, because blowing the creature to pieces would just spread the lethal radiation further, resulting in more deaths. The two scientists propose finding a way to administer a dose of radium to the behemoth, hoping to accelerate the radiation sickness that is already slowly killing it. While they prepare the dose (which takes time, because radium must be handled carefully), the behemoth continues its rampage, destroying electric towers and eventually plummeting through London Bridge back into the Thames.
Karnes and Bickford set their plan into action. A mini-sub with Karnes carries a torpedo filled with radium into the Thames in pursuit of the monster. During an initial pass, the Behemoth takes a bite out of the mini-sub, but Karnes convinces the submarine captain to have another go. This time the sub fires the torpedo into the monster's mouth.
The behemoth roars in pain as the radium accelerates the high radiation levels that were already bringing about its death. Observers in helicopters see steam rising from the ocean, indicating the monster's demise. As Karnes and Bickford climb into a car to leave the area, they hear a radio report of dead fish washing up on the eastern shores of the United States.
The live-action scenes for The Giant Behemoth were filmed in Great Britain, including London. The model-animation special effects were shot in a Los Angeles studio, where they were also optically integrated with live-action footage.
In an odd connection between O'Brien and his most famous creation, stock screams that were used in King Kong can be heard in the scenes where the creature attacks the ferry and when it invades London.
In Video Movie Guide 2002, mention of the stop-action animation was made but with the proviso that "the film monster wasn't bad but [Willis O'Brien] was clearly working with a low budget".
American film critic Andrew Wickliffe considered the preamble to the appearance of the monster in The Giant Behemoth to be more interesting than the rampage that follows, writing, "I'm not sure the British are really suited for giant monster movies. No offense to the Brits, but watching a bunch of folks stand around and keep the stiff upper lip while radioactive monsters from the deep attack London isn't too much fun.".
Regarding a later release of the film in a package with other science fiction features, film reviewer Glenn Erickson observed that The Giant Behemoth was derivative, speculating that "... director Eugène Lourié apparently instructed writers Robert Abel and Alan Adler to repackage his original The Beast from 20,000 Fathoms, copying whole scenes and situations. The structure and script are almost a verbatim clone, right down to the dotty paleontologist".