[Click on the letter 2 times to ENLARGE.]
This letter dated August 2, 1939, was personally delivered to the President on October 11, 1939 by Alexander Sachs, a longtime economic adviser to FDR.
Albert Einstein was acquainted with the Roosevelts and was internationally recognized for his expertise when wrote this letter telling the President about the dangers of a nuclear chain reaction bomb.
After reading the letter, President Roosevelt told his military adviser General Edwin M. Watson, “This requires action.” This later evolved into the "Manhattan Project".