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Listed Building
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Date first listed:
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Ordnance survey map of BLOCK A AT BLETCHLEY PARK
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Statutory Address:

The building or site itself may lie within the boundary of more than one authority.

Milton Keynes (Unitary Authority)
West Bletchley
National Grid Reference:
SP 86531 33960


721/0/10015 BLETCHLEY PARK 28-SEP-05 Block A at Bletchley Park


BUILDING: Adapted spider block.

DATE: 1942

ARCHITECT: Highly-adapted spider block plan purpose-built by Ministry of Works for Government Code and Cipher School

MATERIALS: Steel frame with pre-cast concrete floors and roofs. Painted Fletton brick walls, metal windows.

PLAN: E-plan building, comprising an east-west range with three ranges projecting forward from this to the south. On the east side of the western spur a bay window marks the office of Frank Birch, Head of the Naval Section.

EXTERIOR: Two storeys with flat roof. Regular runs of mainly four-light steel-framed windows to both storeys (some lengthened at some stage) with tile sills. Doors to south ends of each spur. External steel staircases to first floors of west and east spurs. Projecting open-sided porch on north side of the spine range.

INTERIORS: Although the building has undergone considerable alteration to service its post-war uses, until recently most of the corridors and walls were of wartime date. In 2004 the eastern spur and part of the spine range were gutted to create exhibition spaces. Sub-divisions of the building are legible from structural compartments.

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.

Block A, with Block B, was conceived in mid 1941 as an extension to the overcrowded wooden huts and first occupied in August 1942. They formed the first wave of purpose-built structures on the site, responding to the increased volume of decrypts and the desire to create an effective military intelligence centre. Initially it housed the both the Naval and the Air Sections. The former, on the ground floor, took on functions previously carried on in Hut 4. These included intelligence analysis of naval traffic decrypted by Hut 8, non-Enigma cryptography, crib research, and plotting. In addition, Hagelin cipher machines were installed. After analysis material was sent to the Admiralty. The Air Section, on the first floor, included the Meteorological Section (which, for instance, supplied weather forecasts which would help Coastal Command and predict the movements of U-boats and shipping), and SALU (a sub-section mainly concerned with intelligence on German bomber and reconnaissance aircraft). In mid 1943 the Air Section moved to Block F, enabling the Naval Section to take over all of Blocks A and B.

After the war the building - which was considerably adapted for its future uses - accommodated various bodies, notably (early 1950s-late 1970s) a teacher training college and from 1977 the Civil Aviation Authority. The latter left the site in 1993, since when the building has been the responsibility of the Bletchley Park Trust, and stood largely unoccupied for ten years. In 2004 the building was partly stripped out by the Trust to create a new exhibition space.

SUMMARY OF IMPORTANCE: Like Block B, which is already listed, Block A's importance is principally historical, although the physical survival of the building which reflects the scale of the operation at Bletchley is important. The blocks are among the buildings which demonstrate the first instances on the site of the construction of more permanent buildings, ones moreover specifically designed for the personnel and functions which they were to house. They stand markedly in contrast to the small and temporary wooden huts they succeeded. Not only does Block A have a significant relationship to Block B, but also to the lake and landscape and to all the other wartime buildings, several of which it had close operational links with. Bletchley Park is renowned for its part in breaking the German Enigma code, and in contributing to the Allied victory (especially in the Battle of the Atlantic). Block A played an important part in this achievement from 1941 onwards. Architecturally, like Block A, Block B survives externally little altered, and its crisp and functional appearance reflects Bletchley Park's increasing scale and reliance on a large staff and complex electronic machinery. Internally much of the building retains the main components of its wartime layout, although sections of the building have been gutted. 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. 2, 309-49; Feilden & Mawson, Bletchley Park Conservation Management Plan (draft 05, December 2004)


The contents of this record have been generated from a legacy data system.

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This building is listed under the Planning (Listed Buildings and Conservation Areas) Act 1990 as amended for its special architectural or historic interest.

End of official listing

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