60 years ago today, the first atomic bomb to be used in anger upon living people was dropped. This was, of course, Hiroshima in Japan. The bomb was developed at Los Alamos laboratories in the US, and had the destructive power of 20000 tonnes of TNT - by today's standards this is a small bomb.
As the bomb was developed, its builders were aware that the Germans may be working in the same field. Combined with the V2 this would have been disasterous. Even after Germany was defeated, one can make the case that not dropping the bomb would ultimately have cost many more lives on both sides of the conflict.