The Double-Cross System or XX System was a World War II counter-espionage and deception operation of the British Security Service (a civilian organisation usually referred to by its cover title MI5). Nazi agents in Britain – real and false – were captured, turned themselves in or simply announced themselves, 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" (i.e. a double cross). 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. Of the agents from the German intelligence services, Abwehr and Sicherheitsdienst (SD), some were apprehended, while many of the agents who reached British shores turned themselves in to the authorities; others were apprehended after they made elementary mistakes during their operations. In addition, some were false agents who had tricked the Germans into believing they would spy for them if they helped them reach England (e.g., Treasure, Fido). Later agents were instructed to contact agents who, unknown to the Abwehr, were controlled by the British. The Abwehr and SD sent agents over by parachute drop, submarine, or travel via neutral countries. The last 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 had been captured, with the possible exception of one who committed suicide. Early agents Following a July 1940 conference in Kiel, the Abwehr (German intelligence) began an espionage campaign against Britain involving intelligence gathering and sabotage. Spies were sent over from Europe in various ways; some parachuted or came off a submarine. Others entered the country on false passports or posing as refugees. Public perception in Britain was that the country was full of well-trained German spies, who were deeply integrated into society. There was widespread "spy-mania", as Churchill put it. 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. The agents were not difficult to spot, and it became easier still when the German Enigma machine encryption was broken. MI5, with advance warning