 The first months of Bradbury 's directorship were particularly difficult . He had hoped that Atomic Energy Act of 1946 would be quickly passed by Congress and the wartime Manhattan Project would be superseded by a new , permanent organization . It soon became clear that this would take more than six months . President Harry S. Truman did not sign the act creating the Atomic Energy Commission into law until 1 August 1946 , and it did not become active until 1 January 1947 . In the meantime , Groves ' legal authority to act was limited . 
