Editing GCHQ (section)

===Interwar Period===
{{anchor|Government Code and Cypher School}}
In 1919, the Cabinet's Secret Service Committee, chaired by [[Lord Curzon]], recommended that a peacetime codebreaking agency should be created, a task which was given to the [[Naval Intelligence Division (UK)|Director of Naval Intelligence]], [[Hugh Sinclair]].<ref name="johnson44">Johnson, 1997, p. 44</ref> Sinclair merged staff from NID25 and MI1b into the new organisation, which initially consisted of around 25–30 officers and a similar number of clerical staff.<ref>Johnson, 1997, p. 45 and Kahn, 1991, p. 82; these sources give different numbers for the initial size of the GC&CS staff</ref> It was titled the "Government Code and Cypher School" (GC&CS), a cover-name which was chosen by Victor Forbes of the [[Foreign Office]].<ref>{{Cite book|last=Macksey|first=Kenneth|title=The Searchers: How Radio Interception Changed the Course of Both World Wars|year=2003| publisher=Cassell Military|isbn=0-304-36545-9|page=58}}</ref> [[Alastair Denniston]], who had been a member of NID25, was appointed as its operational head.<ref name="johnson44"/> It was initially under the control of the [[British Admiralty|Admiralty]] and located in Watergate House, Adelphi, London.<ref name="johnson44"/> Its public function was "to advise as to the security of codes and cyphers used by all Government departments and to assist in their provision", but also had a secret directive to "study the methods of cypher communications used by foreign powers".<ref>Smith, 2001, pp. 16–17</ref> GC&CS officially formed on 1 November 1919,<ref>Kahn, 1991, p. 82</ref> and produced its first decrypt prior to that date, on 19 October.<ref name="johnson44"/>

[[File:Allidina-Visram.jpg|thumbnail|right|Allidina Visram school in Mombasa, pictured above in 2006, was the location of the British "Kilindini" codebreaking outpost during World War II.]]

Before the Second World War, GC&CS was a relatively small department. By 1922, the main focus of GC&CS was on diplomatic traffic, with "no service traffic ever worth circulating"<ref name="and">{{cite journal |first=Alastair G. |last=Denniston |title=The Government Code and Cypher School Between the Wars |journal=Intelligence and National Security |volume=1 |issue=1 |pages=48–70 |year=1986 |doi=10.1080/02684528608431841 }}</ref> and so, at the initiative of Lord Curzon, it was transferred from the Admiralty to the [[Foreign Office]].<ref>Smith, 2001, pp. 20–21</ref> GC&CS came under the supervision of [[Hugh Sinclair]], who by 1923 was both the Chief of [[Secret Intelligence Service|SIS]] and Director of GC&CS.<ref name="johnson44"/> In 1925, both organisations were co-located on different floors of Broadway Buildings, opposite [[St. James's Park]].<ref name="johnson44"/> Messages decrypted by GC&CS were distributed in blue-jacketed files that became known as "BJs".<ref>Smith, 2001, pp. 18–19</ref> In the 1920s, GC&CS was successfully reading Soviet Union diplomatic cyphers. However, in May 1927, during a row over clandestine Soviet support for the [[1926 United Kingdom general strike|General Strike]] and the distribution of subversive propaganda, Prime Minister [[Stanley Baldwin]] made details from the decrypts public.{{sfn|Aldrich|2010|p= 18}}