It’s been described as a “quiet Sunday morning in December.” Sunday, December 7, 1941 is a day that will forever be remembered as the day Japan attacked the United States. The quiet of that Sunday morning was shattered when an aerial striking force of the Imperial Japanese Navy flew into Pearl Harbor, wreaking devastation and killing more than 2,400 Americans. But why had that particular morning been chosen? Was there a special significance about December 7 or the fact that it was a Sunday morning?

Though it may seem like Japanese officers simply threw a dart at a calendar and landed on Sunday, December 7, there was actually a lot of strategy behind every decision made that affected the attack. They left nothing to chance and wanted to make sure the plan was executed perfectly, and to ensure that, they also needed to carefully consider when the attack should take place.

Why Sunday?

Sunday, December 7

St. Andrew’s Cathedral, Honolulu

Why Japan chose a Sunday of all days actually coincides with why many businesses were closed on the seventh day of the week. During the 1940s, Sundays still held religious significance for many. Japanese intelligence on the United States, some of which was provided by an insider living in the Hawaiian Islands, made it clear that much of the nation was occupied on Sunday mornings with religious services. On that Sunday morning, many military personnel were attending off-base services, leaving the ships in the harbor understaffed in the event of an emergency.

By deciding to attack on a Sunday, Japan had knowingly chosen a day where the United States would not be at full strength. This added to the possibility of the attack remaining a surprise until it was too late to react to it. Japanese officers knew that the United States would be ill-prepared for a Sunday morning attack, especially since those not on leave were relaxing, enjoying the relative quiet of the otherwise busy harbor. It created a peaceful atmosphere that would be completely vulnerable to the surprise attack.

Why December 7?

Sunday, December 7

Before smoke filled the air, the sky was mostly clear

While attacking on a Sunday makes sense, it still leaves the question of why Sunday, December 7 specifically? The answer to that comes down to weather. For the attack to be effectively pulled off, the aerial attack fleet needed good visibility. Any amount of heavy cloud cover would have made it difficult to identify vital targets, and the mostly clear conditions ensured that Oahu was visible to the strike force.

While planning the attack on Pearl Harbor, Japanese officers and Admiral Isoroku Yamamoto took several points into consideration to guarantee the attack was pulled off flawlessly. By choosing a clear-skied Sunday in December, the fleet was able to do precisely what it had intended.

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