How Japan might learn that Pearl Harbor is empty

Japanese observers in Hawaii, including Takeo Yoshikawa, might notice the fleet's departure, but collecting the information was not the same as safely delivering it to the carrier force. The United States might itself announce the movement as a diplomatic display, either immediately or only after the fleet reached the western Pacific. Tokyo would then have to transmit loudly enough for Kido Butai to receive the change without knowing whether American stations were also listening. An acknowledgment could compromise the carrier force's position, while silence would leave headquarters unsure whether the warning had arrived. Repeated broadcasts would magnify the same risk, so even good intelligence in Hawaii might reach the operational commander too late to change the attack plan safely.