Summary

Former explosives factory of 1916 for the Royal Navy. Variously updated and reconstructed until production ceased in 1945, though parts of the site remained in use until 1997.

Source: Historic England

Details

PRINCIPAL ELEMENTS
The monument includes the earthworks, buried remains, foundations, ruins and standing buildings of the former Royal Naval Cordite Factory (RNCF) Holton Heath within three separate areas of protection. This purpose-built complex was principally in operation between 1916 and 1945 and is situated on lowland heathland and was an extensive complex covering some 494 acres (just under 200ha). It was equipped to be largely self-sufficient, with the various ingredients necessary for cordite production being manufactured on-site and transported by a railway network. The site was physically organised according to process and risk, and was essentially divided into different factory departments through which the manufacturing process flowed. Many of the structures on site were built of timber or brick, and many have been demolished. There are, however, extant structures of concrete and/or brick, footings and extensive earthwork remains.

A detailed description of a site of this scale is beyond the scope of this document and is covered in detail by Bowditch and Hayward (1996) and Cocroft (2000) from which the following summary draws heavily. This description does not attempt to describe every feature present, but rather will characterise briefly the remains in each area. The conventions used for various buildings when the factory was operational are shown on historic plans of 1939 and 1946, and for reference are cited here.

DESCRIPTION
As a factory dealing with dangerous materials, safety was of paramount concern. Very many of the buildings at RNCF are protected by earthen traverses to minimise the impact of any explosion from damaging neighbouring structures; some were also completely covered with earth. In addition trees (principally leylandii) were planted alongside some of the buildings as additional blast barriers and for screening. The site also needed to operate efficiently so layout of the whole, and the interconnection by transport between individual processes in the factory, was also of great importance. Where sections of the former railway network are visible they take the form of earthwork embankments or cuttings, while evidence for one of the two charging houses for the smokeless locomotives, which depended on high pressure steam, can also be traced on the ground to the east of Black Hill, close to Blackhill Road. Other communication routes within the site are limited, save for a network of concrete pathways, some of which survive. There are also a number of brick-lined culverts and concrete post alignments, some retaining their iron brackets, which carried pipelines or cables for steam and electricity across the site. In addition, some of the concrete blocks, inscribed with individual building numbers and either set in the ground or mounted on posts, and cast-iron lamp posts installed by Mann Egerton & Co Ltd in 1916, survive across the site.

The service RESERVOIR on Black Hill is semi-circular on plan and divided into two quadrants. Its eastern half has brick piers and a concrete roof; the western half was open until 1934 when concrete piers and steel joists were added to support a concrete roof. The footings of the outlet house and some of its metal pipework survive on the top of the reservoir.

The NITROGLYCERINE (NG) FACTORY is situated in the central part of the site, and is laid out on the lower slopes of Black Hill so that the various ingredients could be moved between buildings initially by gravity within lead-lined gutters (removed). The buildings themselves are inter-linked by a network of cuttings and embankments, some of which were for rubber-wheeled trolleys that were introduced to this part of the site after the explosion in 1931. One of the NG factory’s most distinctive features is the nitrator separator (AB2) of 1936 which is covered by a substantial steep-sided earth mound. It contained a Schmid nitration plant (not extant) which was housed in an arched-roofed, reinforced concrete shell that was lined internally with white glazed bricks, and accessed from a concrete-revetted entrance passage through the south-east side of the mound. The nitrator separator (AB1) of 1916 is to the south-west. Its protective earthwork is lower and is square in profile. Situated between these two structures are the substantial remains of the building which housed the mixed acid storage tanks and is protected by a massive concrete blast wall along the south-east side. To the south are the washing houses (C1-2) where excess acids would be removed from the nitroglycerine. Both have well-formed mounds, though their southern south edges have been clipped by modern development. Other surviving remains include the footings and/or lower parts of the walls of various buildings including cold brine tank houses and a charge house. In addition the sites and traverses of one (E1) of the four paste mixing houses and one (F1) of the paste sheet drying houses, of which there were originally four, survive. The wash settling house (D1) has also been demolished and its site redeveloped. The paste mixing and paste sheet drying buildings are not extant but retain their surrounding traverses, the structures themselves are no longer extant. To the north-east of Black Hill is the NG compressor house which supplied compressed air used to move the acids and NG around the NG plant. It survives as low sections of walling and storage tanks. A length of pipe runs south from here towards the mixed acid storage tanks. Beyond the compressor house is a length of railway cutting.

To the south-west of the NG factory are the earthworks, standing and buried remains of the PRESS HOUSES (P). A new form of press house was developed in the late 1920s for the production of cordite SC, while large horizontal presses to produce rocket propellant and catapult charges were introduced in 1937. The press houses, built on the site of the 1916 guncotton drying stoves, are regularly arranged to either side of a railway cutting that runs north-east to south-west. Each of the houses is surrounded by a large earth traverse with a break in the banks facing the railway to move material in and out. These press houses contained a separate press room, control room, and motor and cutting rooms which were protected by concrete walls. The buildings were of timber construction, but footings, concrete walls faced with internally with buff coloured bricks, and concrete machine bases survive. Associated buried archaeological remains are also likely to survive. To either end of the press houses the railway branches off northwards within a deep cutting to form a loop line that served the later press houses of 1937. These are built of reinforced concrete with steel frames, glass-brick windows, and an internal facing of white glazed bricks. The front part of the press house contained the cutting room, pump room, changing room and a recess for the oven; to the rear, accessed from a corridor was the press room which is covered by an earth mound. There are some variations in the design of several of the buildings; for example, the one to the far left comprises two parallel rooms. The structures (S4-6, F5), mostly drying stoves, on the south side of the railway survive in the form of ruined structures or foundation footprints; the earth traverses are also extant. In addition, several small brick structures including a vacuum plant remain.

North of the press houses, and west of the reservoir, are a group of four REFUGES (air-raid shelters). They are set partially below ground and each one has a concrete entrance which leads to an earth-covered, reinforced concrete tube that is painted white internally. Immediately to the east is the CONTROL TRENCH (OP1) which was added during the Second World War. This large linear earthwork is aligned west-east and contains an underground control room of concrete and brick which was used by the Home Guard for monitoring and communications during the war. It is accessed from the south via a pre-cast concrete tunnel which is adjacent to a brick-lined building that is set into the earthwork and which retains a section of rail track. At the rear of the control room is a metal ladder that leads up to an observation turret on the surface. This squat, circular structure is built of brick with a conical concrete roof and three embrasures. At the east end of the control trench is a small, roofless, brick-built magazine.

To the south of the press houses are the standing remains of the ACETONE FACTORY of 1917. It comprised a granary for storing maize; a cooker house (listed at Grade II and not included in the scheduling) where the maize was reduced to a mash in six cookers; and the fermentation building containing eight aluminium fermentation vessels each within a circular tank; it was served by a railway on its north side. The concrete floor slab of the granary survives alongside the railway embankment, and six of the eight concrete tanks which originally contained aluminium fermentation vessels, remain extant. The tanks are 11.5m in diameter, of reinforced concrete, an unusual material in the fabrication of a chemical plant, and raised off the ground on concrete pillar. Although the building which housed them was demolished in 1934 its original extent can be traced.

To the north of Black Hill and on the west side of Blackhill Road are the remains of one of the three cordite INCORPORATING AND PRESS RANGES (two were demolished when Blackhill Road was created) where mineral jelly and acetone were added and thoroughly blended into the cordite dough. Few upstanding remains of the surviving range (Z) survive and it is not included in the scheduling.

On the opposite side of Blackhill Road are the remains of the ACETONE RECOVERY STOVES, a group of four buildings which are aligned north to south and encircled by a deep railway cutting. The northernmost stove is not highlighted on the 1939 plan which suggests that it was no longer operational by this date. The stoves were sited below the surrounding ground level and surrounded by large protective traverses. The buildings themselves have been demolished, but large quantities of collapsed walling and piles of brick are visible at the three southern stove sites (S1-2, X5). The northern stove survives as a level platform with partitions and other features and a large traverse on its north side. It survives less well than the three stoves to the south and is not included in the scheduling.

Immediately to the east are the CORDITE DRYING STOVES, interconnected by a complex network of railway embankments which survive particularly well. The buildings are arranged in three parallel rows, with a shorter row to the south which contains further stoves and the MAGAZINES. Each stove was tightly encircled by an earthen traverse with a gap for access to and from the railway. The structures survive to varying degrees from foundations slabs to ruined structures. When the picrite factory was added in 1937-38 these buildings were converted for picrite pressing. At the western end of the central alignment of drying stoves are the remains of the BATCH or PACKING HOUSE. It is built of brick and the west, north and east walls of the building survive almost to eaves level with openings for windows supported by brick piers in each of the walls.

The PICRITE FACTORY (picrite was used in large quantities in the production of flashless cordite) achieved maximum production from 1939 and comprises some twenty structures where the various manufacturing processes were carried out. It was approached and served by a railway network which gave access to all the buildings and its route can be traced on the ground. The buildings were either set below the surface or surrounded by earth traverses which remain extant. They were steel-framed buildings with external walls of brick, concrete roofs, and internally faced with white glazed bricks. They survive to varying degrees, including areas of collapsed brickwork to complete flat-roofed structures. A massive arched-roofed concrete cover in which a mixing house (E6) stood survives towards the south end of the complex. To the south-west of the picrite factory, close to Squirrell Corner, is an area that is marked on the 1946 plan of RNCF as dump storage where a number of small storage buildings and laboratories were laid out.

EXCLUSIONS
All modern structures such as gates and fence posts relating to land boundaries and the cooker house building (Grade II) which forms part of the acetone factory are excluded from the scheduling although the ground beneath them is included.

Source: Historic England

Reasons for Scheduling

The former Royal Naval Cordite Factory Holton Heath, which opened in 1916, is scheduled for the following principal reasons:

* Survival: the archaeological remains provide an illustration of the layout and organisation of the site and add significantly to our understanding of the scale and nature of explosives manufacture in the first half of the C20;
* Functional legibility: its specialist purpose and the careful handling which the materials required are well represented, as is the logical production flow and its transport infrastructure;
* Representation: although some of the structures are present at other explosives sites, the diversity of the features and the inter-relationship of the different elements increase the group value of the site and enhance the national importance of the monument as a whole;
* Rarity: of particular significance is the acetone factory where one of the first significant applications of biotechnology was carried out and which was innovative in the introduction of sterile conditions to an industrial process;
* Documentary: the site is well documented with the survival of contemporary plans and more recently published material which adds to our understanding and knowledge of the site and the significance of the archaeological remains.

Source: Historic England

Sources

Books and journals
Bowditch, M R, Hayward, L , A Pictorial History of the Royal Naval Cordite Factory, Holton Heath, (1996)
Cocroft, W, Dangerous Energy, (2000)
Dukes, B, 'The Royal Naval cordite factory at Holton Heath' in Dorset Natural History and Archaeological Society, , Vol. 133, (2012), 166-170
Lawson, B, 'Royal Naval Cordite Factory Holton Heath' in Subterranea, , Vol. 1, (January 2003), 12-13
Websites
The Story of the Royal Naval Cordite Factory, Holton Heath, Dorset, accessed 10 December 2015 from http://www.greenacre.info/RNCF/index.html
Other
Curtis’s and Harvey Ltd Explosives Factory, Cliffe and Cliffe Woods, Medway. Archaeological Survey and Analysis of the Factory Remains. English Heritage, Research Department Report Series no.11-2011, 2013
First World War National Factories: An Archaeological, Architectural and Historical Review, David Kenyon, Research Report Series no. 76, Historic England, 2015
Planning Purbeck’s Future, Purbeck Local Plan Part 1. Adopted November 2012
R N Cordite Factory, Acetone Factory, Holton Heath, Dorset, 1996, Royal Commission on the Historical Monuments in England

Source: Historic England