Of the agents from the German intelligence services, Abwehr and Sicherheitsdienst (SD), while many who reached British shores turned themselves in to the authorities, others were apprehended after they made elementary mistakes during their operations.
The truth was that between September and November 1940 fewer than 25 agents arrived in the country; mostly of Eastern European extraction, they were badly trained and poorly motivated.
Writing in 1972, John C. Masterman (who had, later in the war, headed the Twenty Committee) said that by 1941, MI5 "actively ran and controlled the German espionage system in [the United Kingdom]."
[2][3] Once caught, the spies were deposited in the care of Lieutenant Colonel Robin Stephens at Camp 020 (Latchmere House, Richmond).
A Scot and something of a playboy, Robertson had some early experience with double agents; just prior to the war he had been case officer to Arthur Owens (code name Snow).
In the end Owens was interned for endangering Dicketts' life and for revealing the important information that his German radio transmitter was controlled by MI5.
[7] The whole affair resulted in the collapse of the entire Snow network comprising the double agents Owens, GW, Biscuit, Charlie, Summer and Celery.
[2] Robertson believed that turning German spies would have numerous benefits, disclosing what information Abwehr wanted and to mislead them as part of a military deception.
[8] Robertson's first agents were not a success, Giraffe (George Graf) was never really used and Gander (Kurt Goose; MI5 had a penchant for amusingly relevant code names), had been sent to Britain with a radio that could only transmit and both were quickly decommissioned.
This need caused problems early in the war, with those who controlled the release of information being reluctant to provide even a small amount of relatively innocuous genuine material.
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.
There was even a case in which an agent started running deception operations independently from Portugal using little more than guidebooks, maps, and a very vivid imagination to convince his Abwehr handlers that he was spying in the UK.
This agent, Juan Pujol García (Garbo), created a network of phantom sub-agents and eventually convinced the British authorities that he could be useful.
The British put their double-agent network to work in support of Operation Fortitude, a plan to deceive the Germans about the location of the Normandy Landings in France.
Early battle reports of insignia on Allied units only confirmed the information the double agents had sent, increasing the Germans' trust in their network.
[12] When the Germans received a false double cross V-1 report that there was considerable damage in Southampton—which had not been a target—the V-1s were temporarily aimed at the south coast ports.
When V-1s launched from Heinkel He 111s on 7 July at Southampton were inaccurate, British advisor Frederick Lindemann recommended that the agents report heavy losses, to save hundreds of Londoners each week at the expense of only a few lives in the ports.
[11] From mid-January to mid-February 1945, the mean point of V-2 impacts edged eastward at the rate of a couple of miles a week, with more and more V-2s falling short of central London.