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 Room 40) respectively.[1][2] It was particularly known for its work on codebreaking at Bletchley Park and after the war became the Government Communications Headquarters (GCHQ).
- ^ Gannon, Paul (2011). Inside Room 40: The Codebreakers of World War I. Ian Allan Publishing. ISBN 978-0-7110-3408-2.
- ^ Johnson, 1997, p. 27
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