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I have heard it claimed that until some refugee physists made new calculations it had been thought that one would need a device weighing perhaps 30 tons to creat a nuclear explosion. Such was obviously not usable in military terms

If that had been believed there might have been no Manhatten project.

I am fairly clear that Japan would have been defeated and probably without a full scale invasion.

(I think that Japan might have surrendered conditonally - just keeping emporer- to avoid the risk of Soviet Occupation).

How likely is a war with the the Soviet Union in the absence of nuclear weapons?

How likely is the use of chemical or bio weapons in such a war?
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