World War II

The British Services

MI5 and the XX System

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"The Double Cross System was one of the greatest intelligence coups of the Second World War. J.C. Masterman, Chairman of the Double Cross Committee, concluded that 'we [MI5] actively ran and controlled the German espionage system in this country [Britain].' The Double Cross Committee was known as the Twenty Committee because the Roman numerals, XX, formed a double cross.

"Due to a combination of counter-espionage work prior to the war and signals intelligence during it, MI5 was in a position to monitor and pick up German agents as they were 'dropped' into Britain. These agents were then 'turned' and began working for the British authorities. The preferred communication was via wireless telegraphy (W/T), although secret ink, microphotography and, in some cases, direct contact with the enemy was also employed.

"Initially the Double Cross System was used for counter-espionage purposes, but its comprehensive success provided an excellent conduit for strategic deception, culminating in the D-Day deception operation, known as FORTITUDE. This plan led the Germans into believing that the Pas de Calais was the real landing area of the Allied invasion, rather than Normandy. Further successes were achieved in U-boat and V-weapon deception." From Public Record Office, "New Document Releases: Security Service Records Release 25-26 November [2002]," formerly at: http://www.pro.gov.uk/releases/nov2002_mi5/intro.htm.

Click for materials on deception operations in preparation for D-Day (Operation Fortitude) and on deception operations generally.

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