Double Cross System

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The Double Cross System or XX System, was a World War II anti-espionage and deception operation of the British military intelligence arm, MI5. Nazi agents in Britain were captured or turned themselves in and were then used by the British to broadcast mainly disinformation to their Nazi controllers. Its operations were overseen by the Twenty Committee under the chairmanship of John Cecil Masterman; the name of the committee comes from the number 20 in Roman numerals: "XX".

The policy of MI5 during the war was initially to use the system for counter-espionage. It was only later that its potential for deception purposes was realised. Agents from both of the German intelligence services, the Abwehr and Sicherheitsdienst (SD), were apprehended. Many of the agents who reached British shores turned themselves in to the authorities. Still others were apprehended when they made elementary mistakes during their operations. Later agents were instructed to contact agents in place who, unknown to the Abwehr, were already controlled by the British. The Abwehr and SD sent agents over by a number of means including parachute drops, submarine and travel via neutral countries. The latter route was most commonly used, with agents often impersonating refugees. After the war it was discovered that all the agents Germany sent to Britain had given themselves up or been captured,[1] with the possible exception of one who committed suicide.


Methods of operation

The main form of communication that agents used with their handlers was secret writing. Letters were intercepted by the postal censorship authorities and some agents were caught by this method. Later in the war, wireless sets were provided by the Germans. Eventually transmissions purporting to be from one double agent were facilitated by transferring the operation of the set to the main headquarters of MI5 itself. On the British side, a critical aid in the fight against the Abwehr and SD was the breaking of the German ciphers. Abwehr hand ciphers were cracked early in the war, and SD hand ciphers and Abwehr Enigma ciphers followed thereafter. The signals intelligence allowed an accurate assessment of whether the double agents were really trusted by the Germans and what effect their information had.

A crucial aspect of the system was the need for genuine information to be sent along with the deception material. This need caused problems on a regular basis early in the war, with those who controlled the release of information reluctant to provide even a small amount of relatively innocuous genuine material. Later in the war, as the system became a more coherent whole, genuine information was integrated into the deception system. For example, one of the agents sent genuine information about Operation Torch to the Germans. It was postmarked before the landing, but due to delays deliberately introduced by the British authorities the information did not reach the Germans until after the Allied troops were ashore. The information impressed the Germans as it appeared to date from before the attack, but it was militarily useless to them.

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