Some people interpret Clause 13 of the Potsdam Declaration, which stated that Japan would face "prompt and utter destruction" if they did not agree to an unconditional surrender, was a reference to the atomic bomb. The Declaration was issued on July 26th 1945, and Hiroshima was bombed on August 6th 1945 (as Japan did not agree to the terms laid out by the Declaration).

The Manhattan Project, however, was kept under immense secrecy. The average American citizen (or anyone in the Japanese government and military) would definitely have not been aware of the existence of nuclear weapons, nor could they have ever interpreted Clause 13 to be a reference to nuclear weapons (which the Japanese were aware of on a theoretical basis).