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Listed Building
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Ordnance survey map of HUT 3 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 86459 33996


721/0/10018 BLETCHLEY PARK 28-SEP-05 Hut 3 at Bletchley Park

GV II BUILDING: Wooden hut, standing c. 125m north of the Mansion.

DATE: Three phases: summer 1940, winter 1941, June 1942

ARCHITECT: Ministry of Works for Government Code and Cipher School.

MATERIALS: It stands on a brick plinth, with its superstructure comprising a light timber frame clad with red-painted plasterboard and with gabled and hipped asphalt and asbestos sheet roofs, which c.May 1941 were clad with Kimola board to give protection from incendiaries.

EXTERIOR: It is a single-storey building standing hard alongside and wrapping around the west and north end of Hut 6, reflecting the close working relations between the sections they housed.

INTERIORS: The building was built in three phases: the south range (summer 1940); the western part of the north range (winter 1941); and the much smaller eastern part of the north range (June 1942). Internally the arrangement of rooms shown on a plan of 1943 has been considerably altered, although some of the rooms, together with other walls, plus wartime doors and windows, do survive intact or largely so. In the south block notable survivals are the central corridor, and rooms on its west side for visiting dignitaries and for administration; the Watch Room, on the east side of the north end of the corridor, has been subdivided. In the north block the Index Room, which occupied much of its west end, has also been subdivided.

SUBSIDIARY FEATURES: A brick boiler house was added against the north-west corner of the south range in the winter of 1941 to heat the newly-enlarged hut. A brick blast wall around the south and west walls of the south range was removed in May 1943, at the same time a bollard (which survives)being installed against the south-west corner of the building.

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 3 was built in June 1940, to replace a smaller hut erected in August 1939. It housed an inter-service section to analyse the decrypted material material generated by Hut 6, and specifically 'to translate and annotate high-grade German signals (Enigma and non-morse) and to report the results to Ministries and to Commands in the Field' (English Heritage 2004, vol. 1, 223). Activity in the hut revolved around the Watch and Index rooms, the former lying at the north end of the south range and the latter occupying much of the west end of the north range. The Watch Room's personnel undertook the translation of Enigma decrypts received from Hut 6. Translations were then passed to Army and Air Advisers in the building who assessed the intelligence using index cards in the large Index Room maintained by the Army and Air sections and by a special Research Section formed in March 1941. Communication to government was facilitated by a direct (secret) teleprinter line to London, agreed in May 1941, together with a standard Typex system with a special security setting. Teleprinters were installed in May 1941. Over time, Hut 3 acquired numerous sub-sections, including an air traffic analysis section, and a German Book Room. In February 1943 Hut 3's staff moved to Block D, one of the new purpose-built brick blocks.

SUMMARY OF IMPORTANCE: Hut 3'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). It was in Hut 3 that from June 1940 crucial analysis of decrypted German army and air force communications took place. The twin hubs of the building were the Watch Room, where Enigma and other materials were translated and annotated, and the Index Room which housed the card indexes used in the intelligence analysis. Although architecturally undistinguished, and internally much changed, the building is little altered externally and, with the other huts (notably the adjoining Huts 1 and 6), captures the character of Bletchley in its pre-expansion phase. 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'. Hut 3 has considerable group value in the complex, notably with Hut 6. 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, 216-28; Feilden & Mawson, Bletchley Park Conservation Management Plan (draft 05, December 2004)


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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.

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