Hut 3 at Bletchley Park

Hut 3 at Bletchley Park

A wooden single-storey hut standing approximately 125 metres north of the Mansion, built in three phases between summer 1940 and June 1942 by the Ministry of Works for the Government Code and Cipher School.

The building stands on a brick plinth with a light timber frame clad in red-painted plasterboard. The roofs are gabled and hipped, originally covered in asphalt and asbestos sheet, but clad with Kimola board from May 1941 for protection from incendiary attack. The hut stands hard alongside and wraps around the west and north end of Hut 6, reflecting the close working relations between the sections they housed.

The building was constructed in three phases: the south range in summer 1940; the western part of the north range in winter 1941; and the much smaller eastern part of the north range in June 1942. The internal arrangement has been considerably altered from a plan recorded in 1943, though some rooms, walls, wartime doors and windows survive intact or largely so. In the south block, the central corridor survives, along with rooms on its west side for visiting dignitaries and administration. The Watch Room, which occupied the east side of the north end of the corridor, has been subdivided. In the north block, the Index Room, which occupied much of the west end, has also been subdivided.

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

Hut 3 was built to replace a smaller hut erected in August 1939. From June 1940 it housed an inter-service section analysing decrypted material generated by Hut 6, specifically to translate and annotate high-grade German signals (Enigma and non-morse) and report results to ministries and field commands. Activity centred on the Watch Room and Index Room. The Watch Room's personnel translated Enigma decrypts received from Hut 6, which were then passed to Army and Air Advisers who assessed the intelligence using index cards in the large Index Room maintained by the Army and Air sections and a special Research Section formed in March 1941. A direct secret teleprinter line to London was agreed in May 1941, with a standard Typex system of special security setting. Teleprinters were installed the same month. 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.

Hut 3's significance is principally historic. As an important early building at Bletchley Park, renowned for breaking the German Enigma code and contributing to Allied victory, particularly in the Battle of the Atlantic, it was the site of crucial analysis of decrypted German army and air force communications from June 1940. Although architecturally undistinguished and internally much changed, the building is little altered externally and, with other huts notably the adjoining Huts 1 and 6, captures the character of Bletchley in its pre-expansion phase. The hut possesses considerable group value within the complex, particularly with Hut 6.