The Double-Cross System or XX System was a World War II counter-espionage and deception operation of the British Security Service (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".
The Security Service, also known as MI5, is the United Kingdom's domestic counter-intelligence and security agency and is part of its intelligence machinery alongside the Secret Intelligence Service (MI6), Government Communications Headquarters (GCHQ), and Defence Intelligence (DI). MI5 is directed by the Joint Intelligence Committee (JIC), and the service is bound by the Security Service Act 1989. The service is directed to protect British parliamentary democracy and economic interests and to counter terrorism and espionage within the United Kingdom (UK).
Plan Kathleen, sometimes referred to as the Artus Plan, was a military plan for the invasion of Northern Ireland by Nazi Germany, sanctioned in 1940 by Stephen Hayes, Acting Irish Republican Army (IRA) Chief of Staff.
Roman Garby-Czerniawski was a Polish Air Force captain and Allied double agent during World War II who used the code name Brutus.
The Emergency was a state of emergency in the independent state of Ireland in the Second World War, throughout which the state remained neutral. It was proclaimed by Dáil Éireann on 2 September 1939, allowing the passage of the Emergency Powers Act 1939 by the Oireachtas the following day. This gave sweeping powers to the government, including internment, censorship of the press and correspondence, and control of the economy. The Emergency Powers Act lapsed on 2 September 1946, although the Emergency was not formally ended until 1976.
Arthur Graham Owens, later known as Arthur Graham White, was a Welsh double agent for the Allies during the Second World War. He was working for MI5 while appearing to the Abwehr to be one of their agents. Owens was known to MI5 by the codename SNOW, which was chosen as a play on his last name.
Josef Jakobs was a German spy and the last person to be executed at the Tower of London. He was captured shortly after parachuting into the United Kingdom during the Second World War. Convicted of espionage under the Treachery Act 1940, Jakobs was sentenced to death and shot by a military firing squad. He was not hanged since he was captured as an enemy combatant.
Jan Willem Ter Braak was a Dutch espionage agent working for Germany who operated for five months in the United Kingdom. Ter Braak, whose original name was Engelbertus Fukken, is believed to have been the German agent who was at large for the longest time in Britain during the Second World War, despite his short period of activity. When he ran out of money, Ter Braak committed suicide in a public air raid shelter.
Operation Lobster I was an Abwehr plan to infiltrate three German agents into Ireland, in July 1940. It was part of a wider series of missions carried out within the framework of Operation Lobster during World War II.
In 1940 the Germans decided to send agents and saboteurs to infiltrate Britain from Norway and northern France. This plan was given the codename Operation Lobster. It remained in place despite the collapse of plans for the invasion of Britain in Operation Sea Lion.
Günther Schütz was a German citizen who worked for German Intelligence (Abwehr) during World War II, he was deployed to Ireland, however, after parachuting to the wrong location he was apprehended by Irish police, and spent much of the rest of the war in prison, barring a brief escape.
Colonel Dan Bryan (1900–1985) was an officer in the Irish Army and Director of Military Intelligence G2 during World War II, known in neutral Ireland as "The Emergency", who "masterminded the most sophisticated security operation in the history of the Irish state."
The Abwehr was the German military-intelligence service for the Reichswehr and the Wehrmacht from 1920 to 1945. Although the 1919 Treaty of Versailles prohibited the Weimar Republic from establishing an intelligence organization of their own, they formed an espionage group in 1920 within the Ministry of Defence, calling it the Abwehr. The initial purpose of the Abwehr was defence against foreign espionage: an organizational role which later evolved considerably. Under General Kurt von Schleicher the individual military services' intelligence units were combined and, in 1929, centralized under Schleicher's Ministeramt within the Ministry of Defence, forming the foundation for the more commonly understood manifestation of the Abwehr.
Wulf Dietrich Christian Schmidt, later known as Harry Williamson was a Danish citizen who became a double agent working for Britain against Nazi Germany during the Second World War under the codename Tate. He was part of the Double Cross System, under which all German agents in Britain were controlled by MI5 and used to deceive Germany. Nigel West singled him out as "one of the seven spies who changed the world."
Richard James Hayes was an Irish code-breaker during World War II and was Director of the National Library of Ireland.
Karel Richard Richter was a German spy. Richter was captured on 14 May 1941 after parachuting into the United Kingdom during the Second World War. He was convicted of espionage at the Old Bailey on 24 October 1941, sentenced to death and hanged on 10 December 1941 at Wandsworth Prison.
Jessie Jordan was a Scottish hairdresser who was found guilty of spying for the German Abwehr on the eve of World War II. She had married again after her German husband died fighting for Germany, before she became a spy in Scotland. She was imprisoned and deported to Germany after the war ended.
Nikolaus Ritter is best known as the Chief of Air Intelligence in the Abwehr who led spyrings in the United Kingdom and the United States from 1936 to 1941.
Walter Arthur Charles Dicketts was a British double agent who was sent by MI5 into Nazi Germany in early 1941 to infiltrate the Abwehr and bring back information about any impending invasion of Britain.
Alphons Louis Eugene Timmerman was a Belgian ship's steward who became a spy for the German intelligence agency, the Abwehr, during the Second World War. He was captured by the security services upon his arrival in Britain in September 1941. MI5 officers posed as Timmerman in correspondence with the Abwehr in an attempt to deceive them as to the competence of the British security services. This attempt was unsuccessful as German intelligence officers failed to spot deliberate mistakes in the letters, but did help to disprove the Abwehr's previously good reputation for intelligence work. Timmerman admitted to being a spy and was executed at Wandsworth Prison in 1942.
