It’s well known that as the Truman White House made plans to use the first atomic bombs against Japan in the summer of 1945, a large group of atomic scientists, many of whom had worked on the bomb project, raised their voices, or at least their names, in protest. They were led by the great Leo Szilard. On July 3, he finished a petition to the president for his fellow scientists to consider, which called atomic bombs “a means for the ruthless annihilation of cities.” It asked the president “to rule that the United States shall not, in the present phase of the war, resort to the use of atomic bombs.”
The following day he wrote this cover letter (below). The same day, Leslie Groves, military chief of the Manhattan Project, wrote Winston Churchill’s science advisor  seeking advice on how to combat Szilard and his colleagues. The bomb would be tested two weeks later and dropped over Hiroshima on August 6. For more see my recent book Atomic Coverup  and my book with Robert Jay Lifton, Hiroshima in America.
July 4, 1945
Enclosed is the text of a petition which will be submitted to the President of the United States. As you will see, this petition is based on purely moral considerations.
It may very well be that the decision of the President whether or not to use atomic bombs in the war against Japan will largely be based on considerations of expediency. On the basis of expediency, many arguments could be put forward both for and against our use of atomic bombs against Japan. Such arguments could be considered only within the framework of a thorough analysis of the situation which will face the United States after this war and it was felt that no useful purpose would be served by considering arguments of expediency in a short petition.
However small the chance might be that our petition may influence the course of events, I personally feel that it would be a matter of importance if a large number of scientists who have worked in this field went clearly and unmistakably on record as to their opposition on moral grounds to the use of these bombs in the present phase of the war.
Many of us are inclined to say that individual Germans share the guilt for the acts which Germany committed during this war because they did not raise their voices in protest against these acts. Their defense that their protest would have been of no avail hardly seems acceptable even though these Germans could not have protests without running risks to life and liberty. We are in a position to raise our voices without incurring any such risks even though we might incur the displeasure of some of those who are at present in charge of controlling the work on “atomic power”.
The fact that the people of the people of the United States are unaware of the choice which faces us increases our responsibility in this matter since those who have worked on “atomic power” represent a sample of the population and they alone are in a position to form an opinion and declare their stand.
Anyone who might wish to go on record by signing the petition ought to have an opportunity to do so and, therefore, it would be appreciated if you could give every member of your group an opportunity for signing.