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Pacific 1939-1945: Pearl Harbor

Why was the USA so unprepared for the attack on Pearl Harbor in 1941?

Extract from a report by a British naval intelligence officer

Catalogue ref: WO 208/2081

Extract from a report by a British naval intelligence officer; WO 208/2081

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What is this source?

This source is an extract from a report by a British naval officer soon after the attack on Pearl Harbor.


The officer clearly believed that the Japanese citizens living in and around Pearl Harbor could not be trusted. He was concerned that Japanese citizens in the British possession of Singapore might act as agents for a Japanese attack there.

What’s the background to this source?

WW2 broke out in Europe in 1939. The USA was neutral in the early stages of the war although it was clear that US President Roosevelt was no friend of Nazi Germany or its ally Japan. In Japan, hard line military commanders had become increasingly powerful during the 1930s. Japan had built up an empire in Asia and these leaders wanted Japan to become Asia’s leading power. They knew that the USA would stand in their way and that war with America would happen some time. They decided to try and knock out the US fleet in the Pacific. The plan was to buy time to build up their resources in the Pacific so that Japan would be ready to take on the USA once it recovered from the attack at Pearl Harbor.


By 1941 Japan was a dominating force in Asia. It invaded Manchuria in 1931 and then China in 1937. By 1940 Japan controlled Korea and French Indochina (modern Vietnam). It intended to use these territories as a platform to take control of British territories like Malaya and Singapore, the Dutch East Indies and the US dominated Philippines. After Pearl Harbor this plan worked very effectively. At one point it seemed that even Australia might be under threat from invasion.

It’s worth knowing that...

Hawaii had a large population of Japanese immigrants. Some were Japanese citizens but many others were American citizens as they had been born in Hawaii and grown up there.


During WW2 around 120000 Americans of Japanese descent were put into camps.

How will you use this source?

  1. Study the first paragraph of this source. Does it give you confidence in the accuracy of the rest of the information in the source?
  2. Why did the Japanese attack when they did?
  3. According to the source, did some Japanese in Pearl Harbor know the date? How convincing is this evidence?
  4. What does the writer imply was the significance of the actions of the Japanese girls and the restaurant owner? Do you find this evidence convincing?
  5. Does this source convince you that Japanese spies and infiltrators played a key role in the Pearl Harbor attack?
  6. Has a big event ever happened in your school (e.g. a fire)? Did rumours travel around after the event and how accurate did they turn out to be? Does this affect your view of this source?
  7. Could any parts of this source be used as evidence in your report on the key question?

Use this table to help plan your report.