A nefarious organization is trying to mine a rare radioactive mineral. Towards that end, the head of the organization has a mechanical replica of King Kong built, but the radiation proves too much for it. When members of a submarine crew discover the existence of the real King Kong, the evil organization plans to kidnap both Kong and his discoverers.
Back when I was a kid, I thought this was the worst of the kaijus largely due to the fact that I find one of the central premises (that the best way to mine radioactive minerals is with giant gorillas, and if you don't have one of those, the second best way is to build a mechanical replica of a giant gorilla) to plum the depths of absurdity. I still find it ridiculous, but I can get past that nowadays; it's not a bad kaiju, the evil Doctor Who (nothing to do with the British timelord, but dubbed by Paul Frees) is one of the most memorable villains for one of these movies, and the final battle (with both Kong and mechani-Kong climbing Tokyo Tower) is pretty good. I also think that the Kong outfit here is a definite improvement over the one used in KING KONG VS. GODZILLA . The movie also has an interesting genesis; it was based on a forgotten American cartoon, and was co-produced by Arthur Rankin Jr., part of the production team of Rankin/Bass. Two of the main characters are played by Americans, though, for some reason, Linda Milller was dubbed rather poorly by another actress. As a side note, this is the second movie in a row I've seen to feature a boat wrecked by a giant monster.