Today marks the 75 anniversary of the Potsdam declaration of July 26, 1945. The proclamation by the Americans, British, and Chinese, laid out the terms for Japanese surrender, the alternative being prompt and utter destruction.
The declaration was never sent via diplomatic channels, but within hours, it was sent in English by shortwave, and shortly thereafter, the Japanese translation was broadcast. In addition, over three million leaflets containing the text of the declaration were dropped over Japan by American bombers.
The stations broadcasting the message included KSAI on Saipan, whose 50,000 watt signal on 1010 kHz blanketed the home islands as strong as any Japanese station. Within days, leaflets specifically mentioning Hiroshima and Nagasaki were dropped, warning civilians to evacuate those locations.