From what I recently saw on the History Channel, the first Japanese A-bomb was largely designed and manufactured in North Korea. And during the last days of the war Japan, supposedly, tested an A-bomb prototype.
According to that History Channel episode (and my memory) the Russians destroyed and/or moved everything associated with the A-bomb construction post WWII. This would explain how they got the technology so fast. Also, this may be why North Korea will be off limits for a long time. None of the larger nations including Russia, Japan, and USA want this to be known, hence, why North Korea is such a secluded country.
Is any of this making any sense?
Reasons for each nation to keep this information suppressed, assuming it is true. This is my opinion after watching the History Channel’s episode about Japan’s A-bomb.
1. Russia - No need to brag about stealing the A-bomb technology.
2. Japan - Wouldn't have a leg to stand on if the world new they would have easily used it on the USA if WWII didn’t end when it did.
3. USA – Oops, we shouldn’t have allowed Russia to occupy North Korea after WWII, my (the USA treaty designers) mistake.
PS I think the episode was on the History Channel, but not entirely sure.
