British counter-intelligence had a lucky break early in the war when they uncovered a Welsh double-agent, Arthur Owens, who had been reporting both to SIS and the Abwehr. Owens handed over his codebooks and volunteered to maintain radio contact with the Abwehr under MI5 control. With his help, MI5 were able to intercept several other Abwehr agents as they parachuted into Britain. Each agent captured was offered the choice of imprisonment (if not execution) or feeding misinformation to the Germans. An ad hoc committee called variously the Double-Cross Committee or the Twenty (XX) Committee was set up to control the agents.
Since the agents' hand-ciphered messages were always re-encoded by the Abwehr's Enigma for retransmission, they provided an invaluable crib for breaking into Abwehr daily settings, which enabled more agents to be uncovered both in Britain and abroad. By 1943, the SIS was able to report with confidence that every Abwehr agent in Britain had been either 'turned' or neutralised. This total control of the Abwehr's information sources allowed the Double-Cross Committee to completely mislead the German High Command as to the planned sites of the Sicily and D-Day invasions, for example, as well as the location of V1 and V2 impacts.
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