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U.S. Military Strategy Prior to Dec. 7, 1941

Stationing the Fleet at Pearl Harbor

Admiral Kimmel

Admiral Kimmel. National Park Service photo.

In the 1930s the United States Pacific Fleet was based in California (San Diego, Long Beach, San Francisco), and Washington (Bremerton), all on the West Coast of the U.S. During this time, Japan became very active in invading Manchuria and many major Chinese cities. After the Germans invaded France in 1940, the Japanese also took bases in French Indo-China.

In an attempt to discourage Japanese aggression or invasion in Asia, President Roosevelt decided to move the Pacific Fleet out to Hawaii, about 2,400 miles closer to Asia. The intent was to intimidate Japan, in order to dissuade it from invading all of the smaller countries, and European colonies in the Pacific. These had become particularly vulnerable as Germany was invading European countries in the early years of WWII.

U.S. Belief the First Attack Would be on the Philippines

The Pacific Fleet was the largest fleet in the United States Navy and the original U.S. war plan was based on the fact that the Philippines would be lightly guarded. If the war broke out with Japan, the Japanese would invade the Philippines and conquer it. Next, the United States Fleet, based on the west coast, would prepare itself, sail out past Hawaii to the Philippines, rescue the American Army there, and drive off the Japanese after defeating their fleet. So the mind set was that the attack was going to come in the Philippines as part of a Japanese move into southern Asia.

A Change in U.S. Strategy

General MacArthur, as the Grand Marshal (field marshal) for the Philippines, convinced the U.S. War Department that the Philippines could be defended and that he was raising and training a 100,000 strong Filipino army. As a result, the basic U.S. strategy changed. The United States started increasing the size of the army in the Philippines and MacArthur started working on protection for the most likely invasion beaches, which were to the north of Bataan and Manilla on the Lingayen Gulf.

Aircraft SabotageSecurity at Pearl Harbor

General Short

General Short. US Army photo.

General Short had been ordered to protect aircraft located at Pearl Harbor against sabotage - which was thought might come from the local population which had a large percentage of people of Japanese ancestry. So he placed guards around the perimeters of the army bases and lined up the aircraft in tight rows, in a central location that could be easily guarded.

Three Levels of Alert at Pearl Harbor

General Short had three levels of defense. The first level of alert was for sabotage protection. This alert required all of the ammunition to be stored in a central area under lock and key. All of the airplanes were grouped together wingtip to wingtip in formation out on the middle of the runway where they would be easy to guard from ground attack by small numbers of individuals attempting to conduct sabotage.

Every time Washington and the War Department sent out war warnings, General Short went to level one status and lined everything up to protect it from sabotage. And he would inform Washington of this fact. (This is the alert level which Peal Harbor was under at the time of the Japanese attack).


Alert level two assumed that Washington D.C. would inform Hawaii when war had been declared and at that point preparations would be made to protect Hawaii from a potential attack by an enemy military force.

Once Pearl Harbor had received news of war (not before), weapons, like aircraft, would actually be armed and stationed in revetments, so they would have walls on two or three sides to protect the aircraft from nearby explosions during bombing attacks.

Airplanes would be armed, fueled, and prepared to take off and do battle. The new radar stations would be manned to provide advanced warning. But at level One, none of these preparations would happen. Because level two involved more personnel, more weapons, and was more expensive to conduct, General Short just assumed that an attack would not happen without Washington informing them in advance that war had actually been declared.

Level three, the highest state of readiness, assumed that an attack on Pearl Harbor had already happened and that army personnel would be siphoned off of the air forces and deployed to beach fortifications to repel the invasion. It did not assign a large role to army aircraft.

So in one sense, General Short assumed that the army air force would get the worst end of battle and become essentially non functional as a result of an attack. And he planned that once those planes were destroyed, the 2,000 - 3,000 men in the army air force who were mechanics, armorers, and other air force support, would be available to man the beach defenses. This was the reason he required army air force personnel to take six weeks of infantry training when they arrived in Hawaii.

The concept that Hawaiian defenses were in place to protect the US Navy fleet really didn't penetrate General Short's line of though. And certainly the concept that the Japanese might attack before war was declared, was not in General Short's line of thinking - even though they had done this in the war against Imperial Russia in 1904. General Short was an Army officer and a gentleman, and war, in Western thought, was conducted after war was declared. So there was a certain naivete in that whole generation of Americans that didn't really expect sneak attacks.

Japan's Timing of Declaration of War

On the other hand, the Japanese did not really intend that the attack would be a complete surprise to the United States. The Japanese planned to have their ambassador in Washington D.C. notify the U.S. thirty minutes before the attack on Pearl Harbor. That was perhaps deemed enough time for war etiquette, but not enough time to allow Pearl Harbor to make any preparations for war.

But the Japanese were walking a very fine line and events did not go according to plan. The Japanese ambassadors were not able to decode the message in time to notify the United States until an hour after the attack had actually commenced. By then, the U.S. decoders had already deciphered the message but its language was ambiguous. So the American forces were sent a notification only that the Japanese had broken off negotiations and war was likely.


However, a declaration of war occurring thirty minutes prior to the attack on Pearl Harbor as planned by the Japanese, would not have changed the outcome of the attack. It would have taken thirty minutes for the message to reach Pearl Harbor anyway.

The first action taken by Peal Harbor would have been to relay the declaration of war to the Philippines, as the assumption that the Philippines would be the primary target would not have changed. Additionally, the message would have needed time to be distributed throughout the bases at Pearl Harbor, and for the men on leave to be called back to base.

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