Editing Ultra (cryptography) (section)

===Army and Air Force===
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.

Dissemination of Ultra intelligence to field commanders was carried out by [[MI6]], which operated [[Special Liaison Units]] (SLU) attached to major army and air force commands. The activity was organized and supervised on behalf of MI6 by [[Group captain|Group Captain]] [[F. W. Winterbotham]]. Each SLU included intelligence, communications, and cryptographic elements. It was headed by a British Army or RAF officer, usually a major, 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. In order to safeguard Ultra, special precautions were taken. The standard procedure was for the liaison officer to present the intelligence summary to the recipient, stay with him while he studied it, then take it back and destroy it.

By the end of the war, there were about 40 SLUs serving commands around the world.{{sfn|Calvocoressi|2001|pp=78}} Fixed SLUs existed at the Admiralty, the [[War Office]], the [[Air Ministry]], [[RAF Fighter Command]], 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.{{sfn|Stephenson|2004|p=56}} These units had permanent teleprinter links to Bletchley Park.

Mobile SLUs were attached to field army and air force headquarters and depended on radio communications to receive intelligence summaries. The first mobile SLUs appeared during the French campaign of 1940. An SLU supported the [[British Expeditionary Force (World War II)|British Expeditionary Force]] (BEF) headed by [[John Vereker, 6th Viscount Gort|General Lord Gort]]. The first liaison officers were Robert Gore-Browne and Humphrey Plowden.{{sfn|West|1986|p=138}} A second SLU of the 1940 period was attached to the [[RAF Advanced Air Striking Force]] at [[Meaux]] commanded by Air Vice-Marshal [[Patrick Playfair|P H Lyon Playfair]]. This SLU was commanded by Squadron Leader F.W. "Tubby" Long.