This list entry was subject to a Minor Amendment on 16/07/2020
Hut 4 at Bletchley Park
(Formerly listed as Hut 4 at Bletchley Park, BLETCHLEY PARK)
BUILDING: wooden hut directly south of the Mansion.
DATE: Summer 1939.
ARCHITECT: by Captain Faulkner for Government Code and Cipher School.
MATERIALS: brick plinth, shiplap boards for its exterior walls and a double-pitched roof, now asphalt covered.
PLAN: rectangular, with some later extensions.
EXTERIOR: it is a twelve-bay single-storey structure. At 145 feet it is one of the largest huts on the site.
INTERIORS: internally Hut 4 has been much altered, both during the war and later. A western extension added about 1940 now houses a kitchen servicing a café in the four western bays of the hut. A cupboard door near the north-west corner is the likely location of the entrance to a 1941 teleprinter extension (now lost) which linked Hut 4 and the Mansion. From the café a central corridor leads west, with roughly two-and-a-half bay rooms to the north and south, part of the wartime arrangements. These have original doors and windows. The corridor leads into a three-bay bar with post-war bay window on its south side. Beyond are stores and, finally, a meeting room which occupies an area which in 1943 was divided into three offices.
SUBSIDIARY FEATURES: several buildings (some at least later extensions) are attached to this building, including a small brick boiler house with chimney on the south side.
HISTORY: In 1939 Bletchley Park became a dispersal home to the Foreign Office's Government Code and Cipher School. It became the focal point of inter-service intelligence activities, the place where German codes (notably those encrypted using the Enigma machine) were deciphered, the significance of decrypts assessed, and intelligence passed to appropriate ministries and commands. Bletchley Park has become celebrated for its contribution to the Allied victory, as well as for its contribution to the development of information technology. As the organisation enlarged new buildings had to be provided, firstly wooden huts and, from 1942, more permanent brick blocks.
Hut 4 was probably constructed along with the first group of huts (1,2, the first Hut 3, and 5) by August 1939. Its original occupants and functions are not clear, but in early 1940 at least part of it became home to the German Naval Section (French, Italian, and Spanish Naval Sections were at that time housed elsewhere), analysing decrypted material from the German Navy. Some low-level decryption also took place. Subsequently that section took over the whole hut. It worked closely with Huts 3, 6, and especially 8, responsible for decoding naval Enigma traffic and headed by Alan Turing. About June 1941 the Italian and Spanish Naval Sections were amalgamated with the German in Hut 4, contributing to its overcrowding. In June 1942 `Fish' (the Bletchley Park covername for German encyphered teleprinter traffic) began to be read, and two machines for Fish enciphered messages were installed. In August and September 1942 the Naval Section moved out to Blocks A and B.
For the remainder of the war Hut 4 was occupied by various sections (although retaining Tunny machines, which printed out decyphered high-level German signals traffic) until early 1943) including Military Intelligence, the Japanese Military Section, and parts of WT co-ordination.
After the war the hut was used as the Bletchley Park Club until 1995. Currently it is used as a café and bar by the Bletchley Park Trust.
SUMMARY OF IMPORTANCE: Hut 4's significance is principally historic. It was an important building in the early phase of Bletchley Park, which is renowned for its part in this breaking of the German Enigma code, and in contributing to the Allied victory (especially in the Battle of the Atlantic). From early 1940 its Naval Section carried much of the responsibility for analysing deciphered Enigma material relating to the German Navy (and later the Spanish and Italian navies too). Although architecturally undistinguished (and retaining few features of interest internally) this long hut stands hard alongside the Mansion and its wartime appearance is outwardly little altered. The whole of the hut as here described, including the boiler house, merits inclusion on the list because of its historic significance through its central role in the early part of `the Bletchley story'. This recommendation is informed by considerable English Heritage research, cited below.
SOURCES: English Heritage, Bletchley Park (Architectural Investigations Reports and Papers B/010/2004), vol. 1, 26-38, 229-40; Feilden & Mawson, Bletchley Park Conservation Management Plan (draft 05, December 2004)