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 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 ...

. It was set up during

World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

. 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 Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic se ...

. * MI1c: The Secret Service/SIS. * MI1d: Communications security. * MI1e: Wireless telegraphy. * MI1f: Personnel and finance. * MI1g: Security, deception and counter intelligence. From 1915, MI1(b) was headed by Malcolm Vivian Hay.

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 J ...

was in MI1 during World War I. He transferred to the

Government Code and Cypher School The Government Code and Cypher School (GC&CS) was a British signals intelligence agency set up in 1919. During the First World War, the British Army and Royal Navy had separate signals intelligence agencies, MI1b and NID25 (initially known as R ...

and served there during World War II. John Tiltman was seconded to MI1 shortly before it merged with

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 ...

. In 1919 MI1b and the Royal Navy's (NID25) "

" were closed down and merged into the inter-service Government Code and Cypher School, which subsequently developed into the

Government Communications Headquarters Government Communications Headquarters (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 United Kingdom. Primari ...

(GCHQ) at Cheltenham.

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