Many people wanted the US and UK to drop nuclear bombs on Russia shortly after WWII. That was a real threat to the Soviet Union.
See, for example, Bertram Russell
> "If the whole world outside of Russia were to insist upon international control of atomic energy to the point of going to war on this issue, it is highly probable that the Soviet government would give way on this issue. If it did not, then if the issue were forced in the next year or two, only one side would have atomic bombs, and the war might be so short as not to involve utter ruin."
See, for example, Bertram Russell
> "If the whole world outside of Russia were to insist upon international control of atomic energy to the point of going to war on this issue, it is highly probable that the Soviet government would give way on this issue. If it did not, then if the issue were forced in the next year or two, only one side would have atomic bombs, and the war might be so short as not to involve utter ruin."
The US had plans for sudden nuclear attack against the USSR. (http://books.google.co.uk/books/about/To_Win_a_Nuclear_War.h...)