Hirohito's surrender broadcast was scheduled to begin at noon in Japan.
The recorded address aired at 12:00 Japan Standard Time on August 15, 1945. NHK announcers told the public to prepare for an announcement of the highest importance, and many people gathered around household radios or public listening points. The broadcast was heard across Japan and became the first widely heard recording of the emperor's voice.
The timing was significant because the speech was intended to reach the entire country simultaneously. Hirohito spoke in formal classical Japanese, and the audio was not especially clear, so many listeners did not immediately grasp that he was announcing acceptance of the Allied surrender terms. The speech avoided a simple direct statement that Japan had surrendered.
The broadcast time also helps distinguish the announcement from later events. The written surrender was signed on September 2 aboard USS Missouri in Tokyo Bay. Thus, noon on August 15 marked the public announcement, while the September ceremony formally documented the capitulation.