MI1
MI1 or British Military Intelligence, Section 1 was a department of the British Directorate of Military Intelligence, part of the War Office. 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 "Room 40" were closed down and merged into the inter-service Government Code and Cypher School, which subsequently developed into the Government Communications Headquarters at Cheltenham.