The prospect of Germany developing an atomic bomb was also of great concern to scientists in the United States, particularly those who were refugees from Nazi Germany and other fascist countries. In July 1939, Leo Szilard and Albert Einstein had written a letter warning the President of the United States, Franklin D. Roosevelt, of the danger. In response, Roosevelt created an Advisory Committee on Uranium in October 1939, chaired by Lyman Briggs of the National Bureau of Standards.