Hut 11 at Bletchley Park

Hut 11 at Bletchley Park is a brick building standing north of the Mansion, planned in late 1940 and completed in March 1941. It was designed by the Ministry of Works for the Government Code and Cipher School.

The hut is a squat, single-storey rectangular structure with walls at least 500mm thick and a slightly cambered concrete slab roof 480mm deep, supported on an axial steel beam. This robust construction was intended to protect against blast damage. It is built from brick with metal-framed three-light windows. There are doors in both the east and west gables, although the west door may not be of wartime date. The east doorway is notably wide, possibly to allow the bulky bombe machines to be moved in and out, and has a porch probably added in 1943. Small rectangular vents high in the walls may relate to fans installed in December 1941 to manage the considerable heat generated by the electro-magnetic bombes.

Internally, the hut is now divided into three rooms by plasterboard and stud partitions post-dating 1943. Before this division, when used by the Bombe Section, it was likely a single open space, though a supervisor's room may have been partitioned off.

A lean-to bicycle shelter with brick side walls and an asbestos roof stands adjacent to the east door, probably dating from 1943.

Bletchley Park became the dispersal home of the Government Code and Cipher School in 1939 and developed into the focal point of inter-service intelligence activities, where German codes—notably those encrypted using the Enigma machine—were deciphered. The Hut 11 complex, comprising Huts 11, 11A, and 11B (the last demolished after the war), housed the Bombe Section. Bombes were electro-magnetic devices developed by Gordon Welchley, Alan Turing, and Harold Keen from a concept conceived by the Poles in the late 1930s. They provided an automated means of testing hypotheses for the daily settings of Enigma machines by working through the 150 million million possible settings. The first bombe was delivered to Hut 1 in March 1940. Hut 11 was the first brick-built structure on site and superseded the timber-framed and crowded Hut 1 when the bombe machines moved there in March 1941. Nine bombe machines were apparently installed initially. After Hut 11A was constructed in February 1942, the bombes were relocated and Hut 11 was thereafter mainly used for training operators. Later in the war, when larger numbers of bombe machines were housed on outstations elsewhere, Hut 11 served as a store for the WRNS.

In 1945 the hut was handed over to the Ministry of Works direct labour organisation, which used it as carpenters' workshops and stores. When the Bletchley Park Trust was formed in 1992, Hut 11 was refurbished to house a display about the history of the bombe.