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Western Europe 1939-1945: D-Day

Why was D-Day successful?

The role of the intelligence services

Extract from a German intelligence report that was intercepted by British intelligence

Catalogue ref: HW 1/2784

Extract from a German intelligence report; HW 1/2784

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What is this source?

This is an extract from a German intelligence report that the British intelligence services were able to intercept in 1944.


By 1943 British intelligence services had cracked a number of German codes. What was even more valuable was that the Germans were unaware of the extent to which their codes had been cracked.

What’s the background to this source?

By late 1942 the tide began to turn against Germany. From 1943 to 1944, British Empire and US forces began a build up of troops and equipment to drive the Germans out of the lands they had invaded in 1940. The landings took place in June 1944.


German naval forces and aircraft closely watched the Allies’ preparations. It was simply not possible to hide a force as large as the D-Day invasion force but the Allies did try very hard to keep the Germans guessing about exactly where the invasion would take place.

It’s worth knowing that...

The fact that the Germans did not know that the Allies knew what they were thinking was incredibly useful. Apart from any other advantages, it allowed the Allies to see whether their plans to deceive the Germans were working.

How does this source help us to understand why D-Day was successful?

  1. What does the source tell us about what the Germans knew?
  2. The Germans did not know the British were intercepting their reports. Is that obvious from this source?
  3. How much of the information in this source is correct?
  4. How would you sum up the main value of this source to the historian?
  • Will you include this source (or part of it) in your storyboard?
  • If you do use it, what are the main points you will make in your caption?

Use this framework to plan your storyboard.