8.9 BLOCK H AND ASSOCIATED HUTS Summary

8.9 BLOCK H AND ASSOCIATED HUTS

(SP 86330 34060)

Summary

Block H was the last significant building to be erected at Bletchley Park during the
Second World War. It was built between May and September 1944, as an annex to
the 'Newmanry' (working on the deciphering of the 'Fish' series of encrypted German
teleprinter transmissions) in nearby Block F. Of reinforced concrete, with a T-
shaped plan, its main features were two spacious machine rooms, built to
accommodate six Colossi. The Colossus machines, often cited as the World’s first
programmable electronic digital computer,1 were built during 1943 by Tommy
Flowers, based on designs by Max Newman. Unlike the bombes, the Colossi were
all housed on site at Bletchley Park. Originally housed in the southern annex of
Block F; the Colossus II was location in purpose-built accommodation in the
southern end of Block H. The more conventional northern range of the building held
offices and store rooms.

After the war Block H was used by the Post Office training establishment at
Bletchley Park, and the northern range was heavily altered. The machine rooms,
however, remain largely intact and lay claim to being the first structures in the world
erected specifically for electronic computers. In 1994 the Bletchley Park Trust
reopened the building as a museum, including a replica Colossus. Its rather isolated
position in the north-west corner of the site results from the demolition of
neighbouring Block F in 1987.

Historical Background

Plans for Block H (fig. 8.9.1) were approved on 25 May 1944, and the building was
ready for occupation on 17 September. Designed as a 13,000 sq ft extension to the
‘Newmanry’ in Block F, Block H was needed primarily to house Colossi 5 to 11 (the
others being in Block F). It comprised two vast machine rooms (each 3,000 sq ft),
and a more conventional wing for offices and storage. After the war it housed part
of a GPO training establishment.2

The immediate built environment of Block H has changed greatly since the end of
the war. Since the demolition of Block F (1987) and the WRNS canteen (see
below), it has been isolated in the north-west corner of the site, and is somewhat
dominated by Faulkner House (built 1974). Furthermore, it is clear from map

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evidence that, despite their wartime character, the complex of brick huts adjoining
Block H to the north-east dates from the post-war period. The northernmost of
these huts first appears on the Ordnance Survey map of 1968, while the south hut
and link bay had been built by 1970. A detached hut, lying parallel to the south hut,
was built at the same time but had been demolished by 1992. Although this
complex is clad in post-war brickwork, its portal frame is identical to that used
throughout Block H, the roofing materials match those used throughout Block H, and
the metal-framed windows are of a design that would be expected in the 1940s, not
in the 1960s or 1970s.

Figure 8.9.1 The east machine rooms of Block H from the north-east (© English Heritage AA044285)

It must be concluded that the complex of huts to the north-east of Block H was
erected with components from a demolished wartime building. The same is true of
Hut 24, located south of Block H. Hut 24 – although mentioned in June 1944 - first
appears on the Ordnance Survey map of 1970, and must have been erected/re-
erected after 1968.3

The building(s) reused to construct the complex to the north-east of Block H, as well
as Hut 24, would have closely resembled Block H, and were probably built around
the same time, towards the end of the war. Parts of the WRNS Canteen, which

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stood east of Block H from December 1944 until circa 1968, may have been used. It
is unlikely, however, that that structure could account for all of the components and
fittings reused in the present buildings.

The Newmanry and Testery in Blocks F and H

Tunny, the most prolific and productive of the German Fish traffic (enciphered
teleprinter transmissions), was scrambled by a machine known as the Lorenz.4
From 1942, the research section charged with studying Tunny was split into two
sections: the Newmanry (led by Max Newman, a Cambridge mathematics don) and
the Testery (led by Major Ralph Tester, formerly ICI’s representative in Germany).
The Newmanry recovered cipher settings and the Testery produced decodes. The
machines deployed by Newman were Robinson (or Heath Robinson, available from
June 1943), Super Robinson (available from late 1943) and Colossus (available
from February 1944). These fulfilled a similar role to that of the bombes in
deciphering Enigma traffic, but unlike the bombes, all Colossi were housed at
Bletchley Park. The Bletchley Park historical report, 'The General Report on Tunny',
provides technical information about these machines, but also includes detailed floor
plans of Block F and Block H -- the buildings which eventually housed the Tunny
sections -- as they were in 1945.5 Block F had been completed in autumn 1943,
Block H in September 1944. The spread of the Tunny sections over two buildings,
albeit adjacent, proved inconvenient, but Block H seems to have been built because
it was considered unwise to concentrate so much machinery in one building.
Colossi 1 to 4 were housed in Block F, Spurs N and Y, and Colossi 5 to 10, and
possibly 11, in Block H.

Processing Fish traffic involved several different stages, distributed between Blocks
F and H. The starting positions for a Colossus run were determined by hand
methods of statistical analysis, and the final 'scores', indicating the most probable
settings for the first five wheels each day, were tested on Robinson or Tunny
machines. A second set of wheels were worked out in the Testery, and clear
messages were printed out in the Tunny Room in Block F, Spur W. This decoded
material was read by the Cribs section in Block H and passed to the Fish Watch in
Hut 3 (Block D, Spur G). Tapes and various other material was stored for future
reference. The section eventually occupied Spurs W and X in Block F, in addition to
Spurs N and Y, and the whole of Block H.

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Building Analysis: Block H

Block H is located to the west of the empty site formerly occupied by Block F. It
adopts an inverted ‘T’ shape, with a south range comprising a central boiler house
flanked by machine rooms, and a north range containing various offices and stores.

Figure 8.9.2 Block H in 1945, redrawn from TNA:PRO HW 25/5 (Evans 2003, 70)

South Range – Boiler House

The centre of Block H is occupied by a two-storey structure accommodating a boiler
house and water tank (fig. 8.9.2). Its most distinctive feature is the square chimney
which rises from the slightly cambered roof, together with a tank. The walls are of
fletton brick, laid in English bond and painted cream. The plinth is covered in
cement render. To west, north and east, this structure abuts single-storey ranges.
Above the double-pitched roofs of the ranges to west and east, the upper floor (not
accessed: store and tank room) is lit by two rectangular metal-framed windows with
opening casements; they have concrete lintels and tile sills. The south front has two
windows and a doorway at ground level, and a loading door and a window above.
All of the windows are metal framed, and have narrow concrete lintels. The
doorway appears to be in its original position, but the louvred door is of post-war
date. The small closet window to its left also appears to be original, but the larger

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window beyond this occupies an expanse of infill which suggests that it has replaced
double doors, perhaps loading doors or a large hatch for a coal store. There is a set
of loading doors directly above this, at first-floor level. To its right, a small window
lights a stair bay; this is the only window on this façade to have a tile sill.

The floor inside the boiler house is of shuttered concrete, with extra reinforcement
provided by a steel post and girder. At ground level, the building contains two
rooms. The room to the front (originally coal store?) opens directly into the closet
under the concrete staircase without the intervention of a doorway. It has a rough
concrete floor (with pebble inclusions). The width of the door leading into the boiler
room to the rear has been reduced. The boiler room comprises two sections,
differentiated by height, and does not admit any natural light. The lower front
section no longer contains machinery, although two low plinths remain. The higher
rear section still houses three Britannia boilers, which are now oil fired (two fuel
tanks, each of 10500l capacity, are located to the south of Block H). The floor is
tiled (some tiles display the name ‘West Stourbridge’). Steelwork supports a water

tank on the upper floor, above the boilers. The I-section stanchion was made by

Shelton, while the hefty girder was manufactured by Appleby Frodinghay; lighter,
unmarked girders flank the square stack in the rear wall. The structural materials
used in this boiler house are quite different from those of the wings to east and west,
with which it appears to be contemporaneous.

South Range – Machine Rooms

An area to the rear of the boiler house always formed a passageway between the
east and west wings of Block H. In later years, the inner bays of the wings were
enclosed to create transverse corridors along the east and west sides of the boiler
house. The east wing is 10 bays long, the west wing 12 bays (fig. 8.9.2). Each wing
was two bays deep, constructed with a double portal frame carrying a valley roof.
There is a sill of ‘Marston’ bricks, coated in cement render. The long walls are clad
in clay blocks, while the end walls are of brick, laid in English bond. Brick buttresses
project from the centre and corners of the gable walls, which do not incorporate
standard end trusses. The original windows had wooden frames and tile sills: few of
these survive, the majority having been replaced by metal frames with wooden sills,
probably in the 1960s. The roofs are covered by corrugated asbestos sheets and
have ridges with circular terminals.

These wings, together with the north wing of Block H and reconstructed additions
and outbuildings (see below) are standard huts, designed by the Ministry of Works

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and Planning and published in August 1942.6 The ‘MOWP Standard Hut’ was
'capable of rapidity of erection and has lasting qualities which would be of much
service at the termination of the war'.7 It could be adapted for myriad functions and
could be clad in a variety of materials, depending upon supply. After foundations
were prepared, the standard framework of reinforced concrete was erected. Main
frames comprised ribs bolted to bracketed posts and held at the apex by a
continuous bar; end frames comprised four (or more) posts with flat tops carrying a
lintel. Once this was up, the roof covering -- usually corrugated asbestos cement
sheeting -- was put in place. A photograph of 1942 shows a ridge with a circular
terminal. Wall panels and prefabricated windows were erected together. When
hollow clay blocks were used, as they were for Block H, their external face was
painted. It was estimated at a hut could be completed in approximately 200 man
hours. The east and west wings of Block H are of particular interest, as each
comprised two standard huts erected side by side to create a much deeper space
than was normal. The absence of standard end trusses suggests that they may
have been truncated – or that there was an intention to extend them.

Apart from a partition creating a separate room for engineers in the end bay of the
west wing, of which there is now no sign, both wings were originally open. They
were used as machine rooms, and housed six Colossus machines (nos. 5 to 10)
and Super Robinsons.8 Colossi 5 to 8 were in the west machine room; 9 and 10,
with the Super Robinsons, in the east machine room. Work on the assembly of
Colossus No. 11 - destined for the east machine room - stopped in May 1945.9 By
1945, 15 engineers were employed to maintain these machines.

At some time, a spine wall was erected under the valley of each wing, and a number
of other walls were inserted in the east wing. The south side of the east wing is
currently used as a workshop, where a replica Colossus machine is being built. The
north side of this wing is used partly for storage and partly for museum displays.
The north side of the west wing appears to be fitted out as a computer room, while
the south side contains museum displays.

A covered way on the west side of the west wing probably dates from the late
1960s. It has corrugated asbestos sides and a monopitch roof formed from
transparent corrugated sheets. It leads to a detached building of two storeys (the
Navaid School, see below), built with a steel frame and flat roof in the early 1960s.

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North Range – Offices and Stores

A 26-bay range runs north from the boiler house. Like the machine rooms, it has a
concrete portal frame (with an expansion joint between bays 9 and 10, counting
from the south). The north truss comprises four posts, arranged in pairs to either
side of the apex; the standard L-shaped corner post is visible on the north-west
corner, while that to the north-east is now embedded in modern brickwork. The
north gable wall is filled with brickwork, while the long walls are of clay block. The
windows are of very simple joinery. Each one has two central lights which hang on
top hinges and open outwards. The roof is of corrugated asbestos sheeting,
boarded underneath. Conduits for electrical wiring hang from collars close to the
apex.

Figure 8.9.3 Block H, north range corridor, looking south (© English Heritage AA044286)

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A corridor runs through the west side of the building from north to south (fig. 8.9.3).
Many of the doorways in the brick wall on the east side of the corridor have been
repositioned, and patching suggests that some rooms once benefited from borrowed
lights. The doors are unpanelled and have post-war handles and simple
architraves; they were probably replaced in the 1950s or 1960s. The rooms are
separated from one another by brick walls. They do not contain many original
features: most of them have suspended ceilings and modern radiators; some have
modern wallpaper and carpets. Most of this is out of character for Bletchley Park.
The radiators in the corridor, however, are older, and could be original.

A much-altered six-bay sanitary annex opens off the seventh bay on the west side.
It has a concrete frame, clay block walls, wooden windows, a corrugated asbestos
roof, and a corrugated asbestos gable end. The end truss comprises four posts,
arranged in pairs to either side of the apex, in addition to the usual L-shaped corner
posts. The annex is entered through a brick lobby with a flat roof, and has been
completely modernised internally. This annex corresponds with a transverse
entrance corridor on the east side of the range.

The rooms in this range are mostly now devoted to museum displays. Numbering
bays from south to north, the room which originally occupied bays 1 to 6 inclusive
held the 'H Registry'.10 This was a branch of the main Registry in Block F, Spur N,
and held copies of the master punched paper tape intercepted at Knockholt for used
by the Newmanry code breakers. The room has been subdivided.

The much-altered room in bays 8 and 9 was, according to the 1945 plan, Mr Maile's
office. A doorway gave Mr Maile direct access to the room occupying bays 10 to 15.
This was the 'Computery' with 'Cribs' in the north-west corner. Maile, although he
has not been identified, was probably in charge of this section. It is also possible,
however, that what was meant was Mrs Miles – a nickname for a machine. The
Computery housed WRNS, 16 on each shift, trained in the mathematical techniques
involved in convergent rectangling, a method which eliminated unlikely wheel
settings, indicating the best start positions for a Colossus run. The Cribs section,
manned by five German linguists, read decoded material, before sending it to the
Fish Watch in Hut 3 (Block D) for translation, analysis and forwarding. It is unclear
why the Cribs section should have been located in a corner of the Computery.

The corridor did not continue through the northernmost part of this range, bays 16 to
25. These bays were divided into two rooms by a wall between bays 21 and 22.

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The first room was referred to as 'Room D', while the second room had no name.
Both rooms were probably used for storage. It is known that by October 1944 a
store room in Block H was being used to house captured German and Italian cipher
equipment.11 There is no sign of the exterior doorway in bay 25, which is shown on
the 1945 plan. It is clear from that plan that every transverse wall in this range –
with the exception of the walls in the entrance bay (bay 7) - have been moved.
Scars in the brickwork of the corridor wall generally support this evidence.

Adjoining Huts to North-East

As stated above, the complex of brick huts to the north-east of Block H was built in
at least two phases in the late 1960s (fig. 8.9.4). This complex comprises two huts
connected to one another, and to the north range of Block H, by corridors.

Figure 8.9.4 Huts to the east of Block H from the south-east (© English Heritage AA048038)

The northernmost hut is 11 bays long, and has a corridor running through its south
side. The parallel southernmost hut is 14 bays long, with a transverse corridor
running through the seventh bay, and continuing through the east side of the north
hut to Faulkner House. Both huts have concrete portal frames which are identical in
form and construction to those used throughout Block H, but instead of being clad in
clay blocks, the outer walls are of brick, laid in stretcher bond. The type of brick

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used -- a dark red colour with a textured surface -- is clearly of post-war date and
might easily date from circa 1968-70.

Both huts have double-pitched roofs covered with corrugated-asbestos sheets, and
have asbestos ridges with circular terminals. The gable walls contain five windows,
with two small windows flanking the central window in each case. Externally, the
windows have sloping red-tile sills. They contain metal frames, and the window
furniture is marked with the name of the manufacture: 'Ideal'. The internal sills are
of yellow quarry tiles. The radiators positioned under the corridor windows (brackets
marked ‘neo-classic’), and those in the southern hut, are evidently older than those
in the rooms of the northern hut. Incongruously, most of the rooms have been
refurbished for museum displays and have suspended ceilings, carpets and,
occasionally, wallpaper. Original internal walls are of painted brick, laid in stretcher
bond, and there is evidence that the corridor walls once incorporated borrowed
lights.

Male and female lavatories occupy a structure opening off the west side of the
three-bay corridor that links the north and south huts. It has a slightly cambered
roof. The interior has been modernised.

Faulkner House

Faulkner House, a two-storey steel-framed building with a flat roof, is said to have
been built to the north of Block H in 1973-74 for British Telecom, at first for the GPO
engineering section, but from 1980 for management training.12 The date is suspect,
as a building with the same outline is shown on the Ordnance Survey map of 1970,
and a site plan of 1969. On balance, it was probably built in 1968. It was served by
the boiler house in Block H, with large external insulated pipes running along the
west side of the building. The area in front of Faulkner House, where Block F once
stood, appears to have been called Faulkner Green in recent years. The building
became redundant in 1993, but was brought into partial use by the Bletchley Park
Trust in July 1994.

Navaid School

Standing to the west of Block H, this is a detached building of two storeys and 11
bays, built with a steel frame and flat roof in 1964-65. The bays contain large areas
of glazing. The architects were Bernard Sunley & Sons Ltd.13 The building appears

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to have been disused since the Civil Aviation Authority ceased its operations in the
Park in 1993.

WRNS Cafeteria (demolished)

Approximately 250 WRNS were employed in the Newmanry alone, and in November
1944 a WRNS cafeteria was erected on the east side of the north range of Block H.
It opened on 4 December.14 At this time, the main cafeteria had ceased to supply
meals to service personnel. The WRNS cafeteria was in charge of a WRNS officer
and staffed by WRNS cooks and stewards. It provided meals for all Naval
personnel, and at its peak served 1000 meals a day.

This building was demolished between 1968 and 1970, and some of its components
may have been reused in the complex to the north-east of Block H (see above). A
very faint plan of the building survives in the archives at Bletchley Park. It is
captioned 'Bletchley Park Conversion of Engineers Depot to New WRNS Canteen',
and is dated 1944.

The canteen was U-shaped, comprising a broad east range, with two narrower
ranges projecting from its west side. The east range contained the boiler room,
kitchen and kitchen stores. The mess room was in the centre. The south range
held a restroom and lavatories, and the north range had an ante room and 'war
room' in addition to lavatories.

Hut 24

This straightforward detached hut, located south of Block H, was moved from
elsewhere between 1968 and 1970.15 It is constructed with an eight-bay concrete
portal frame, of the same type that is used throughout Block H. Each bay is filled
with painted fletton bricks laid in stretcher bond (note, the original buildings used
English bond for external walls). The windows have metal frames; they are very
similar to those in the north-east ranges of Block H, but have different fittings. The
roof is covered in corrugated-asbestos sheets. The entrance, on the east side, is
sheltered by a brick porch with a lean-to roof. Inside, the building remains open to
the roof and is not subdivided by internal walls. It is currently used as a store and
contains cages. The floor is covered in brown linoleum, and radiators (pre-1970
style) stand under the windows. The underside of the roof is boarded over.

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8.9 BLOCK H: NOTES

1. GCHQ Covernames, 38 and Copeland in Smith and Erskine 2001, 343.
2. GCHQ Huts and Blocks, 43.
3. GCHQ Huts and Blocks, 30.
4. See Wylie in Smith & Erskine 2001, 317-341.
5. TNA:PRO HW 25/5.
6. The Builder 28 August 1942, 176-177.
7. The Builder 28 August 1942, 176.
8. See TNA:PRO HW 25/5 for positions of machines.
9. TNA:PRO HW 25/40.
10. TNA:PRO HW 25/5.
11. GCHQ Huts and Blocks, 43.
12. White 1996, 7 and 9.
13. White 1996, 2.
14. GCHQ Huts and Blocks, 32.
15. Ordnance Survey maps.

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