Double Cross System Totally Explained

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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 and 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 system 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. 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.

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 cyphers. Abwehr hand cyphers were cracked early in the war, and SD hand cyphers and Abwehr Enigma cyphers 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 didn't 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.

Operation outside the United Kingdom

It wasn't only in the United Kingdom that the system was operated. A number of agents connected with the system were run in Spain and Portugal. Some even had direct contact with the Germans in occupied Europe. One of the most famous of the agents who operated outside of the UK was Tricycle. There was even a case where 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, Garbo, created an entire network of phantom sub-agents and finally succeeded in convincing the British authorities that he could be useful. He and his phantom sub-agents were absorbed into the main Double Cross system, and he became so respected by the Abwehr that they stopped landing agents in Britain after 1942. They thus became wholly dependent on the spurious information which was fed to them by Garbo's network and the other Double Cross agents.

Results

Masterman expressed the opinion that as a consequence of Double Cross's efficacy, by early 1941, "we [MI5] actively ran and controlled the German espionage system in this country [UnitedKingdom]." This was confirmed after the end of the war.

Operation Fortitude and D-Day Landings

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 invasion of France. Allowing one of the double agents to claim to have stolen documents describing the closely guarded invasion plans might have aroused suspicion. Instead, agents were allowed to report observing insignia on soldiers' uniforms and unit markings on vehicles. The observations in the south-central areas largely gave accurate information about the units located there: large Operation Quicksilver forces. Reports from southwest England indicated no troop sightings, when in reality many units were housed there. Any military planner would know that to mount a massive invasion of Europe from England, Allied units had to be staged around the country, with those that would land first nearest to the invasion point. German intelligence used the agent reports to construct an order of battle for the Allied forces that placed the center of gravity of the invasion force opposite Pas de Calais, the point on the French coast closest to England and therefore a likely invasion site. The deception was so effective that the Germans kept 18 reserve divisions near Calais even after the invasion had begun at Normandy, lest it prove to be a diversion from the "real" invasion at Calais.
The Allies were willing to risk exposing the Double Cross network to achieve the needed surprise for the Normandy invasion. However, early battle reports of insignia on Allied units that the German armies encountered only confirmed the information the double agents had sent. Some of the double agents were informed in radio messages from Germany after the invasion that they'd been awarded the Iron Cross.

Use against V-2 rockets

When the German V-2 rocket became operational in September, 1944, the Germans asked their still credible spy network in Britain to send reports of exactly where and when each rocket landed. The British took advantage of this opportunity to feed the Germans false impact reports relating to North London, concocted to make the Germans think that they were overshooting their target and to reduce the range of the rockets. This saved many lives, but was a difficult moral choice since the British were in effect deciding which of their citizens would be bombed. Croydon, in South East London, was particularly affected by V-2 rockets, effectively being sacrificed for the sake of central London. A famous agent used against the V-2 rockets was Eddie Chapman, otherwise known as Codename Zigzag.

Double Cross agents

(partial list)

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