In the case of Behemoth the Sea Monster (the film is also known as The Giant Behemoth) the monster wreaks havoc on London not Tokyo. Before that the monster kills some Cornish fishermen and lots of fish.
The earlier part of the film works better to be honest as you don't actually see the monster, after the unveil of the beast later on it does descend into a bit of a model building destroying romp. The monster scenes are pretty well done though. The budget wasn't huge. Lots of people unconvincingly run around in a British version of panic.
The main problem with the film is the British-ness of it all. I'm not sure stiff-upper-lip characters work that well when the enemy is a giant sea monster and not the Luftwaffe.
Overall its not a bad film but its not very original...
