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Atomic weapons were born from the fear that Hitler's Germany would dominate the world with a monopoly of atomic bombs. The initiative for their development came from Dr Leo Szilard, a Hungarian-born refugee from fascism, who obtained the support of Albert Einstein. Einstein, a German-born Jew and a life-long opponent of German militarism, was then living in self-imposed exile in the United States of America. On 2 August 1939 he wrote to the President Roosevelt, warning of the danger that Germany might develop the bomb:
Some recent work by E. Fermi and L. Szilard, which has been communicated to me in manuscript, leads me to expect that the element uranium may be turned into a new and important source of energy in the immediate future. Certain aspects of the situation seem to call for watchfulness and, ff necessary, quick action on the part of the administration. I believe therefore that it is my duty to bring to your attention ... that extremely powerful bombs of a new type may ... be constructed. I understand that Germany has actually stopped the sale of uranium from the Czechoslovakian mines which she has taken over ...
The USA was not at that time at war and so Einstein's warning did not meet with an energetic response. On 7 March 1940 Einstein, again after an approach from Szilard, wrote a second and more urgent appeal. Preliminary work on bomb manufacture then started, shortly after this second appeal, and by the time they joined the war, U S government and military officials knew that 'extremely powerful bombs of a new type' could be constructed in the way suggested by Szilard and Fermi. In fact the decision to go ahead and build an A-bomb was taken on 6 December 1941 - the day before the Japanese attack on Pearl Harbor which brought America into the war.
In the next four years the scientists worked feverishly to develop atomic weapons in advance of Germany. Enrico Fermi, Leo Szilard, Niels Bohr, Hans Bethe and Joseph Rotblat were among the many Europeans who worked for the project (despite the fact that some were not even American citizens). Several British nuclear scientists also participated. All were united in their fear of what might happen if Hitler were to get the atomic bomb first.
But by November 1944 it was clear that Germany was not in fact making such a bomb. In December 1944 Rotblat, who later became Professor of Physics at St Bartholomew's Hospital Medical College, London, left the project because it no longer seemed necessary. In the spring of 1945 Szilard and Einstein again wrote to Roosevelt, this time with a quite different purpose: to warn him of the dangers which would face the post-war world from the development of atomic energy.
On 8 May 1945 the European war ended and it was confirmed that Germany had never seriously considered building an atomic bomb. The $2,000 million project need never have begun. And there no longer seemed any need to continue with it, since it was known that the Japanese, who were still fighting, had no intention or possibility to make such a bomb. At this time the scientists had not even got as far as building a prototype bomb.
Already the more far-seeing were becoming concerned about the long-term implications of atomic weapons. Einstein, Szilard and Bohr had all attempted in different ways to warn the politicians of the coming dangers. They felt that the bomb project should be abandoned and the emphasis switched to peaceful uses of nuclear energy.
After 8 May this feeling began to be shared by more and more of those who had worked to build the bomb. A poll of these atomic scientists was taken and only 15 per cent wholeheartedly favoured its military use against Japan.
Nonetheless, work on the bomb continued with renewed urgency.