Government Communications Headquarters

The British signals intelligence and cybersecurity agency, descended from Bletchley Park

Overview

GCHQ began in 1919 as the Government Code and Cypher School, the cryptanalytic successor to wartime Room 40. Its wartime home at Bletchley Park broke the Enigma cipher and produced the Ultra intelligence that many historians credit with shortening the war by as much as two years. Postwar it joined the 1946 UKUSA agreement binding it to the American NSA, and 2013 disclosures described its Tempora fiber optic interception program. Today it also leads the cybersecurity defense of the United Kingdom.