GCHQ

The British signals intelligence and communications security agency, successor to GC&CS.

Description based on the Crypto Museum's crypto glossary.¹

According to GCHQ, its predecessor, the Government Code and Cypher School, was formed around 1919 as a single signals intelligence organisation by merging military units from the First World War. In 1939, after moving to Bletchley Park, it was given the cover name GCHQ; breaking German communications, especially those enciphered on the Enigma, contributed significantly to the Allied victory. In 1946 the agency left Bletchley Park and, after a short spell in the London suburbs, moved to Cheltenham.^2,3

GCHQ's legal basis is the Intelligence Services Act 1994, which according to SIS officially acknowledged the existence of both MI6 and GCHQ for the first time. GCHQ's cooperation with the NSA rests on the UKUSA Agreement of 1946, the nucleus of the Five Eyes alliance.^4,5

More in the service card: GCHQ (Government Communications Headquarters).