Soon after daylight on July 27, 1945, Tokyo radio monitored the Potsdam Declaration issued in the name of the three major Allied powers —the United States, Britain and the Soviet Union — then engaged in the war against Japan.

In the declaration, the three governments agreed that Japan should be given the opportunity to end the fighting. They called on Tokyo to "proclaim now the unconditional surrender of all Japanese armed forces and to provide proper and adequate assurances of their good faith in such action. The alternative for Japan is prompt and utter destruction."

Although it was an ultimatum, a little carrot went along with the club. The declaration promised that acceptance would ensure that Japan would neither be enslaved as a race nor destroyed as a nation.

It made no mention of the means that would be used to bring about Japan's immediate and total destruction. However, the orders had already been issued that would lead to the dropping of the atomic bomb on Hiroshima. These could, and almost certainly would, have been canceled if there had been a positive response from Tokyo. Whether the Potsdam declaration was warning enough will no doubt be debated for centuries to come.