Bletchley Park was the central site for British (and subsequently, Allied) codebreakers during World War II. It housed the Government Code and Cypher School (GC&CS), which regularly penetrated the secret communications of the Axis Powers – most importantly the German Enigma and Lorenz ciphers.
According to the official historian of British Intelligence, the "Ultra" intelligence produced at Bletchley shortened the war by two to four years, and that without it the outcome of the war would have been uncertain.