What Led to the Japanese Attack at Pearl Harbor? Part 2

Japanese Zero fighters fly a mission of destruction to Nanzheng, China, 26 May 1941 (public domain via Wikipedia)

The Military Build-Up to December 7, 1941 — What happened in the last days of peace before the collision between the United States and Japan?

In July 1941 the Japanese leadership made the fateful decision to go to war with the United States.

A short time before, its troops had gained control of the southern half of French Indochina (colonial territories in Southeast Asia comprised of Cambodia, Laos, and certain regions of Vietnam), giving them a strategic launch point to conquer southeast Asia and the Philippines.

President Franklin D. Roosevelt signs the Declaration of War against Japan, December 8, 1941. National Archives

American President Franklin D. Roosevelt, recognizing Japan’s threat to America and many other countries, ordered all of Japan’s assets in the United States frozen. In addition, he imposed immediate sanctions and suspending the sale of steel and scrap metal. Perhaps most serious were cancellations of all shipments of oil to Japan.

Japan’s leaders, desperate in knowing their country had only two years of oil in reserve, accused the United States of economic strangulation. When no actions resulted, they realized immediate actions had to be taken. They settled on a two-prong strategy.

First, diplomatic actions would be attempted to restore relations with the United States. A Japanese diplomat was sent to Washington to try to mend relations and resume a normal trade relationship between the two countries.

At the same time, the American fleet — the only naval force that could thwart Japan’s designs on southeast Asia — presented a serious naval threat. Japan planned to destroy it.

In spring 1940, Franklin D. Roosevelt had deployed the American naval fleet to its base at Pearl Harbor, Hawaii. He believed being nearer to places America would need to defend at war – Philippines, Wake Island, Guam – would be an advantage.

Japanese Naval Commander Isoroku Yamamoto thrilled to Roosevelt’s decision to place the ships at Pearl Harbor. The Japanese leader believed a surprise attack there by his airmen could deal a severe blow to America’s Pacific fleet.

After months of planning, Japan decided to use six of its best aircraft carriers for the operation. Transporting 350 planes, they would move in from the north and launch a massive air strike. Thus, Japan’s primary obstacle to domination in target areas would be eliminated by the single decisive stroke.

For the operation to succeed the Japanese modified some of its weapons — torpedoes to run in shallow harbor conditions at Pearl Harbor and bombs capable of penetrating the decks of American battleships.

As final preparations for war were completed, Hideki Tojo, Prime Minister of Japan, ordered negotiations to continue in Washington.

In November 1941, as the Japanese diplomat negotiated with the American secretary of state, American cryptologists broke the Japanese code. By reading messages sent to the Japanese ambassador, the Americans knew Japan was up to something.

However, by now, it was too late. The Pearl Harbor strike force was trained and ready for action.

During the first week of December, sailors of United States Pacific fleet were slowly gearing up for war, unable to anticipate it was on their very doorstep. They spent time on maneuvers, practiced gunnery and air raid drills, and honed their skills at sea.

On Friday, December 5, 1941, they relaxed as their vessels sailed back to Pearl Harbor. For the first time in months the entire battle line was in port. Usually, when one battleship left for maneuvers, another ship pulled into their spot.

Sailors submit to regular inspections aboard ship. Photo courtesy Bill Smith whose story is in We Gave Our Best: American WWII Veterans Tell Their Stories

On Saturday, December 6, men of the Pacific fleet enjoyed shore leave at bars and parties in Honolulu into the wee hours of Sunday. Each knew his training schedule, which included daily inspections, would resume on Monday morning. Almost everyone assigned to the USS Arizona was aboard ship by 1:00 am.

To the north, 180 miles from Oahu, Japanese aircraft carriers steamed into attack range. For nearly two weeks, crews had battled heavy seas and rain in the north Pacific which was typical weather for that time of year in winter. Commercial ships avoided that area, making it a safe route to travel undetected.

Japanese submarines off of Oahu’s southern coast took up their final positions, making ready to launch their midget subs.

Japanese airmen had one final briefing. Some took time to pray for victory. All knew that just over the horizon the Americans sat, unaware that their last moments of peace for a very long while, were at hand.


Next week: Strike! The Japanese Move In on Their Target

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