Enigma cipher machine

A bigger picture

Ultra intelligence was not always used to its fullest. When Enigma was first broken, some British commanders did not take the intelligence produced seriously. In certain cases, cover stories had to be invented to protect the intelligence source and if these could not be supplied in time, the intelligence could not be used. However, intelligence from Bletchley Park contributed to the success of many Allied campaigns.

Coventry Cathedral; 1940


© IWM (Art.IWM ART LD 709)

It has been speculated that Ultra intelligence revealed German plans for a bombing raid on Coventry, but that no action was taken in order to conceal the fact that the Allies had broken Enigma. It is now generally agreed that while Ultra had intercepted and decoded massages about a raid, they were unable to identify the location.

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An Allied convoy in the Atlantic; 1941


© IWM (C 2647)

In the 1941 Battle of the Atlantic, Ultra allowed the British to intercept and decode Kriegsmarine communications, enabling them to divert Allied convoys carrying essential supplies away from the U-boats’ patrol stations.

Convoys of ships.

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The German invasion of Crete; 1941


© IWM (A 4154)

The British commander in Crete knew when and where German airborne troops would attack, but was ordered not to reorganise his forces, as this intelligence had been provided by Ultra.

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HMS Kite on an anti submarine patrol; 1944.


© IWM (A 21989)

In 1942, Germany increased the complexity of the encryption used by the Kriegsmarine, which took ten months for Bletchley to break. After this second breakthrough, and with additional air support, the Allies were able to locate and attack U-boats in mid-Atlantic.

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HMS Argonaut; 1942


© IWM (A 13445)

The code breakers contributed to the North African campaign by providing intelligence that enabled the Royal Navy to attack German supply routes. This photograph shows the ship in harbour after a successful night action with an enemy convoy bound for Tunisia.

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D-Day; 6 June 1944


© IWM (B 5245)

Ultra intelligence enabled the Allies to anticipate the build up of enemy counter-attacks and the directions from which they would come. This photograph shows commandos coming ashore on Gold Beach.

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Enigma cipher machine