How Japan Kept Pearl Harbor a Surprise

April 26, 2017

To a civilian thinking about the logistics of a surprise attack on a military base, it seems almost impossible to pull off. We tend to imagine untouchable bases protected by the best military defense and watched over by enough detection equipment that even a seagull flying hundreds of miles away could be spotted. Of course, Pearl Harbor was over 75 years ago and technology and the nation's precaution have changed quite a bit, but Japan’s ability to fly into Hawaiian airspace unnoticed wasn’t without ingenuity on their part.

Movement in the Shadows

US cryptograph

The United States government was well aware of the tensions rising with Japan. In fact, cryptographers were working around the clock to decipher the latest Japanese intelligence that crossed their desks. In the days leading up to the attack, nothing was believed to be out of the ordinary, even for the personnel in charge of pinpointing the location of the Japanese Imperial Navy. How would that be possible? The United States should have been well aware of any movement in the Pacific by pinpointing whether or not the chatter was stemming from Japan’s coast.

While the fleet traveled from Japan to its destination, the radio operators who typically transmitted from the ships remained behind, creating the illusion that the transmissions were being sent aboard vessels still moored off Japan’s coast. The massive fleet was able to move without worry of their position being pinpointed by American interceptors.

The Spy

Takeo Yoshikawa

To pull off such a complex feat, it always helps to have somebody on the inside. For the Japanese, that was Takeo Yoshikawa , who was known to the Americans as vice-consul Tadashi Morimura. Under his guise, Yoshikawa was able to survey Pearl Harbor and activity in the nearby waters. The spy divulged everything he could to his commanders, including where the battleships were moored, that the aircraft carriers were in international waters, and that approaching from the north would be met with no air patrols.


The Perfect Day

When planning on taking a military base by surprise, the best day to launch an assault is one where much of the workforce is away. Choosing a quiet Sunday in December wasn’t something done at random. Thanks to reports from their man on the inside, the masterminds behind the attack knew that a Sunday morning would be the ideal time to attack. Even if they had been spotted coming in, the number of action-ready manpower would have been considerably smaller than during the week.

In the early hours of the morning of December 7,1941, many sailors were either heading to shore for a little R&R—or simply enjoying their breakfast—but no one was prepared for the incoming waves of attack that would soon decimate much of Pearl Harbor, leaving thousands dead and injured.

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