MI1 or British ''Military Intelligence, Section 1'' was a department of the British Directorate of Military Intelligence, part of the

War Office The War Office was a department of the British Government responsible for the administration of the British Army between 1857 and 1964, when its functions were transferred to the new Ministry of Defence (MoD). This article contains text from t ...

. It was set up during World War I. It contained "C&C", which was responsible for code breaking. Its subsections in World War I were: * MI1a: Distribution of reports, intelligence records. * MI1b: Interception and cryptanalysis. * MI1c: The Secret Service/SIS. * MI1d: Communications security. * MI1e: Wireless telegraphy. * MI1f: Personnel and finance. * MI1g: Security, deception and counter intelligence. In 1919 MI1b and the Royal Navy's (NID25) "

Room 40 Room 40, also known as 40 O.B. (old building; officially part of NID25), was the cryptanalysis section of the British Admiralty during the First World War. The group, which was formed in October 1914, began when Rear-Admiral Henry Oliver, the ...

" were closed down and merged into the inter-service Government Code and Cypher School ( GC&CS), which subsequently developed into the

Government Communications Headquarters Government Communications Headquarters, commonly known as GCHQ, is an intelligence and security organisation responsible for providing signals intelligence (SIGINT) and information assurance (IA) to the government and armed forces of the Unit ...

(GCHQ) at Cheltenham.

Oliver Strachey Oliver Strachey CBE (3 November 1874 – 14 May 1960), a British civil servant in the Foreign Office, was a cryptographer from World War I to World War II. Life and work Strachey was a son of Sir Richard Strachey, colonial administrator and ...

was in MI1 during World War I. He transferred to GC&CS and served there during World War II. John Tiltman was seconded to MI1 shortly before it merged with

Notes

References

What happened to MI1 - MI4?
* Updated and extended version of ''Action This Day: From Breaking of the Enigma Code to the Birth of the Modern Computer'' Bantam Press 2001 * Gannon, Paul, ''Inside Room 40: The Codebreakers of World War I'', Ian Allan Publishing, 2011, {{DEFAULTSORT:Mi1 Cryptography organizations Defunct United Kingdom intelligence agencies 1910s establishments in the United Kingdom Military units and formations disestablished in 1919 United Kingdom in World War I Military communications of the United Kingdom