A Special Liaison Unit (SLU) was a unit within the British military during the Second World War tasked with disseminating intelligence from the

Ultra Ultra may refer to: Science and technology * Ultra (cryptography), the codename for cryptographic intelligence obtained from signal traffic in World War II * Adobe Ultra, a vector-keying application * Sun Ultra series, a brand of computer work ...

program in

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

to military commanders in the field.

Origin

The breakthroughs at

Bletchley Park Bletchley Park is an English country house and Bletchley Park estate, estate in Bletchley, Milton Keynes (Buckinghamshire), that became the principal centre of Allies of World War II, Allied World War II cryptography, code-breaking during the S ...

in April 1940 when cryptographers succeeded in deciphering four small messages regarding Luftwaffe personnel led senior

MI6 The Secret Intelligence Service (SIS), commonly known as MI6 ( Military Intelligence, Section 6), is the foreign intelligence service of the United Kingdom, tasked mainly with the covert overseas collection and analysis of human intelligenc ...

agent F. W. Winterbotham to consider how such decoded information would be handled once it became more plentiful. The Chief of MI6,

Stewart Menzies Major General Sir Stewart Graham Menzies, (; 30 January 1890 – 29 May 1968) was Chief of MI6, the British Secret Intelligence Service (SIS), from 1939 to 1952, during and after the Second World War. Early life, family Stewart Graham Menzies ...

, gave "permission to set up a completely new organisation for the translation, distribution and complete security of the decoded signals...". Winterbotham formed ''Special Liaison Units'' attached to each field headquarters that received Enigma. The distribution of Ultra information to Allied commanders and units in the field involved considerable risk of discovery by the Germans, and great care was taken to control both the information and knowledge of how it was obtained. Liaison officers were appointed for each field command to manage and control dissemination. A key part of the solution was arranging for the secure delivery of information from

to the various commanders, and making sure that they did nothing to give away the secret that Enigma was being read.

Personnel

Dissemination of Ultra intelligence to field commanders was carried out by

, which operated Special Liaison Units (SLU) attached to major army and air force commands. Each SLU included intelligence, communications, and cryptographic elements. An SLU consisted of a few RAF officers and enlisted men, low in rank to avoid drawing attention which made it difficult to award military decorations at the appropriate level. The communications element of each SLU was called a "Special Communications Unit" and was manned by army personnel. The unit was headed by a British Army or RAF officer, usually a

major Major most commonly refers to: * Major (rank), a military rank * Academic major, an academic discipline to which an undergraduate student formally commits * People named Major, including given names, surnames, nicknames * Major and minor in musi ...

, known as "Special Liaison Officer". The main function of the liaison officer or his deputy was to pass Ultra intelligence bulletins to the commander of the command he was attached to, or to other indoctrinated staff officers. Technicians within the units were all at the

sargeant Sargeant may refer to: People * Sargeant (surname), a list of people with the surname Places * Sargeant, Minnesota, U.S. * Sargeant Township, Mower County, Minnesota, U.S. See also *Sergeant Sergeant (Sgt) is a Military rank, rank in use b ...

level.

Protocol

In order to safeguard Ultra, special precautions were taken. They received Ultra messages by radio from Britain, carefully encrypted in Britain's strongest

cipher In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...

. The standard procedure was for the liaison officer to present the intelligence summary to the recipient, stay with him while he studied it, perhaps answer questions and then take it back and destroy it. Messages were to be kept under lock and key. The commander was the usual recipient and often the only person cleared to know where the information came from, although at some HQs one or two deputies might also cleared. Ultra recipients were not allowed to transmit, repeat or refer Ultra signals. Ultra recipients were not allowed to voluntarily place themselves in a position where they could be captured, which could create friction with more active commanders. In some large headquarters, there was a special security reading room.

Progress

The first mobile SLUs appeared during the French campaign of 1940. An SLU supported the British Expeditionary Force (BEF) headed by General Lord Gort. The first liaison officers were Robert Gore-Browne and Humphrey Plowden. A second SLU of the 1940 period was attached to the

RAF Advanced Air Striking Force The RAF Advanced Air Striking Force (AASF) comprised the light bombers of 1 Group RAF Bomber Command, which took part in the Battle of France during the Second World War. Before hostilities began, it had been agreed between the United Kingdom ...

Meaux Meaux () is a Communes of France, commune on the river Marne (river), Marne in the Seine-et-Marne Departments of France, department in the Île-de-France Regions of France, region in the Functional area (France), metropolitan area of Paris, Franc ...

commanded by Air Vice-Marshal P H Lyon Playfair. This SLU was commanded by Squadron Leader F.W. "Tubby" Long. Mobile SLUs were attached to field army and air force headquarters and depended on radio communications to receive intelligence summaries. By the end of the war, there were about 40 SLUs serving commands around the world. Fixed SLUs existed at the Admiralty, the

War Office The War Office has referred to several British government organisations throughout history, all relating to the army. It was a department of the British Government responsible for the administration of the British Army between 1857 and 1964, at ...

, the

Air Ministry The Air Ministry was a department of the Government of the United Kingdom with the responsibility of managing the affairs of the Royal Air Force and civil aviation that existed from 1918 to 1964. It was under the political authority of the ...

RAF Fighter Command RAF Fighter Command was one of the commands of the Royal Air Force. It was formed in 1936 to allow more specialised control of fighter aircraft. It operated throughout the Second World War, winning fame during the Battle of Britain in 1940. The ...

, the US Strategic Air Forces in Europe (Wycombe Abbey) and other fixed headquarters in the UK. An SLU was operating at the War HQ in Valletta, Malta. These units had permanent teleprinter links to Bletchley Park.

Origin

Personnel

Protocol

Progress

Special Security Office

References

Bibliography