This can be quite debatable. Some people would say it was useful as it ended WW2 in the Pacific after Germany surrendered but some would say it wasn't useful as the use of the atomic bombs was 'out of order' and 'over the top'. The usefulness depends on how you look at it and where would it be useful.
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2 atomic bombs and 2 million HE bombs and 5 million incendiary fire bombs
None. The first atomic bomb was dropped decades after World War 1 finished. Atomic bombs weren't used in war until World War II.
See: Atomic Bombing of Hiroshima and Nagasaki.
The atomic bomb wan't completed untill 1945
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