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Pacific 1939-1945: Pearl Harbor

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

On the morning of December 7th 1941 Japanese aircraft and submarines attacked the US Pacific fleet in its base at Pearl Harbor, Hawaii. The fleet was devastated and it was pure luck that the most important ships in the fleet, the US aircraft carriers, were out at sea. Why was the USA taken so completely by surprise?

Your task

Your task is to study the sources and reach an official judgement on why the US was taken so much by surprise at Pearl Harbor in 1941. Your report should cover at least some of these issues:

  • The work of Japanese 5th columnists
  • Japanese military tactics and equipment
  • The efficiency (or inefficiency) of the American forces
  • General attitudes in the USA as a whole
  • The possibility that President Roosevelt sacrificed Pearl Harbor

Use this table to help you plan your report.

Extension question

Was Pearl Harbor a conspiracy?

Study the Pearl Harbor Conspiracy Theory in more detail here.

Clip from British newsreel called Pearl Harbour – First Pictures, January 1942

Catalogue ref: BP190242131817
Courtesy of ITN/Source, London.

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What is this source?

This source is a British newsreel feature from January 1942. It shows the aftermath of the Japanese attack on Pearl Harbor in 1941.


The actual attack took place on December 7th 1941 but it would have taken some time to get the film edited and approved for use with a British audience. There was probably a lot of discussion about how to present the news without damaging morale too much in Britain.

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 North East China in 1931 and then moved deeper into the country in 1937. By July 1941, Japan had flooded French Indochina (now Vietnam) with troops. 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..

The US Pacific fleet had two main bases, Pearl Harbor in Hawaii and San Diego in California. San Diego would have been out of range from Japanese attack.


Although the damage was very severe, the most important ships in the fleet, the US aircraft carriers, were out at sea. This was to prove decisive in the outcome of the Pacific War.

How will you use this source?

  1. Try playing this newsreel clip without sound. Does it confirm that US forces were taken completely by surprise?
  2. What aspects of the attack does the commentary focus on?
  3. How are the Japanese referred to in the clip?
  4. 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.

Now open the source box