How Japan might learn the fleet has sailed

Takeo Yoshikawa, the professional Japanese naval intelligence officer working under consular cover, found local people of Japanese ancestry notably uncooperative and Americanized. He gathered observations around Pearl Harbor and sent them from the consulate in the Purple diplomatic code. Those reports still had to pass through the Foreign Ministry to the navy, imposing delay before they could influence operational decisions. A public American announcement after the fleet had cleared harbor could therefore become the fastest strategic warning to Tokyo. Delaying that announcement until the sortie was safely outside the narrow entrance would deny Japan the especially vulnerable moment when scouts were ahead but the battle line still lacked sea room.