It was called The Manhattan Project. This video is an instructional record of the times they lived in and the degree the USA government committed resources to have it all happen.
One could say, it would be better to prevent the development of such technology, but, if it didn't happen in the USA it would have happened elsewhere and would the outcome today be so stark and aimed at non-proliferation.
At the first test occurred, the scientists backed away from using the technology as a weapon. They had an idea about the magnitude of the technology, but, it's final development was a surprise to even them. They told the USA military they did not want this unleashed in the world.
Their protestations were taken seriously and the President wanted to notify Japan of the weapon and the willingness of the USA to use it. The weapon itself and not the use of it in war was to be a deterrent. The rest is history.
