Einstein’s Letters of 1939 and 1945 and Szilard’s Petition of 1945
There were certainly a number of cautionary flags waved at the Executive Branch in the period just before the atomic bomb was first used against a Japanese target. As I wrote in an earlier post here, Dwight Eisenhower was adamantly opposed to the use of the bomb on a city, preferring an example to be made of the thing on an unpopulated area; in his memoirs, General Spaatz (who had received the only written communication authorizing the use of the bomb) was privately against using the weapon on a city. As early as 1939 Albert Einstein famously communicated with Franklin Roosevelt his concerns on the possibility of the terrifying nature of a bomb produced by his early efforts and those of Fermi and Szilard and many others. In all Einstein wrote four letters to the President, the first part of the first letter is shown below: