The estate in Bedfordshire purchased in 1936 by the Secret Intelligence Service chief, Adm. Sir Hugh Sinclair, as a war station for his organization. The first full dress rehearsal took place during the Munich Crisis of 1938 when the SIS and the Government Code and Cypher School established themselves in the mansion and a few huts constructed in the grounds.
In September 1939, following cryptographic success with Abwehr hand ciphers, the staff at “BP” or “Station X” was increased significantly, and by the end of the war 12,500 mathematicians, linguists, analysts, engineers, couriers, and support personnel were working on intercepted enemy communications traffic at the site in three eight-hour shifts.
In 1945 the renamed Government Communications Headquarters (GCHQ) was transferred to Eastcote in Middlesex, leaving only a training unit at Bletchley, which remained in one of the purpose-built offices on the estate until 1988.