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Listed Building
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Ordnance survey map of HUT 11A 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 86397 33992


721/0/10024 BLETCHLEY PARK 28-SEP-05 Hut 11A at Bletchley Park

GV II BUILDING: Wooden hut, standing c.120m north of the Mansion.

DATE: October 1941-February 1942.

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

MATERIALS: Brick structure, with a gabled roof carried on lightweight steel trusses covered with corrugated sheeting.

PLAN: Rectangular.

EXTERIOR: Single-storey building, west of and aligned with Hut 11 and hard against the south side of Hut 10. It has a wide east entrance with a pair of doors, probably to facilitate the bulky bombe machines which it housed to be brought in and out. Steel-framed windows in all four walls are small and high set, probably to keep wall space unencumbered and perhaps furthermore to give protection from blast.

INTERIORS: Concrete floor. The current arrangement of rooms is very similar to that during the war, with small rooms (wartime offices and lavatories) at the east end and an open space (now partly subdivided) at the west. The latter was where the Hut's bombe machines stood. Seven of these are marked on a plan drawn by one of the Wrens who operated them, each bombe identified by name (`Agnes', `Chaos', `Dumbo' etc.). Several trunked vents leading into the roof space presumably relate to the building's wartime air conditioning.

The building is in good condition externally. Internally it is also well preserved with only some superficial deterioration such as buckled plaster ceilings.

SUBSIDIARY FEATURES: A lean-to engine room was added in June 1942. The Milton Keynes Model Railway Club has added a small lean-to against the south wall to accommodate part of a model railway track.

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.

The Hut 11 complex, comprising Huts 11, 11A, and 11B (demolished after the war), housed the Bombe Section, superseding Hut 1 which was timber framed and cramped.. Bombes were electro-magnetic devices, developed from an original idea conceived by the Poles (who called their machine `Bomba' (probably because it had weights which dropped - like bombs - when correct wheel settings were identified) in the late 1930s and developed into a more sophisticated form in 1939 by Gordon Welchman, Alan Turing, and Harold Keen. Bombes were an automated means of testing hypotheses (called menus) for the daily setting of an Enigma machine by working through the 150 million million settings its rotors, rings, and plugsettings were capable of. By November 1939 the first bombe machine had been ordered from the British Tabulating Machine Co. of Letchworth, and this was delivered to Hut 1 in March 1940.

The first of the three huts, 11, was planned in late 1940 and completed in March 1941. Hut 11A was begun in mid 1941 and its fitting out completed (including air conditioning to combat the heat generated by the bombes) in February 1942. Hut 11A was intended to replace, not augment Hut 11, and when the former was complete all the bombe machines were moved into it. Later in 1942, as outstations (built in the grounds of local country houses) took on the role of housing the vastly increased number of bombe machines needed for decryption, Hut 11A developed into the control and communications centre linking those outstations with Huts 6 and 8. Some bombes, however, remained in 11A either as training aids or specialist or experimental machines, for instance `Funf' which was employed to solve the reverse Enigma used by the Abwehr (the German Secret Service).

In 1945 the Hut 11 complex was handed over to MOW direct labour organisation which used it as carpenters workshops and stores. When the Bletchley Park Trust was formed in 1992 Hut 11A became the club room of the Milton Keynes Model Railway Club.

SUMMARY OF IMPORTANCE: Hut 11A's importance is principally historical. Bletchley Park 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). The Bombe Section in the Hut 11 complex was an essential component of the code breaking network, human and mechnical. The bombes were moved to the purpose-built Hut 11 from the vulnerable wooden Hut 1 in March 1941, Hut 11 being the first wartime brick building at Bletchley Park. Hut 11A, which largely superseded it, stands alongside. During 1942 virtually all Bletchley Park's bombe machines were housed in it, and its scale in comparison to Hut 11 shows the rapid increase in the number of bombe machines being manufactured at this time which in turns marks Bletchley Park's development into a global SIGINT (Signals Intelligence) hub capable of processing increasingly vast amounts of data. It survives little changed externally, while internally its layout is only slightly altered. 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, 300-8; 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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