In 1939 , Albert Einstein and Leó Szilárd wrote a letter to President Franklin D. Roosevelt warning him that the Germans might be researching the development of atomic weaponry and that it was necessary that the United States fund research and development of its own such project . Roosevelt agreed , and the result was the Manhattan Project — a top-secret research program administered by Major General Leslie R. Groves , Jr . The first bomb was tested successfully in the Trinity nuclear test on July 16 , 1945
Trinity nuclear test
Trinity (nuclear test)
Surrender of Japan