More information : Site of a Gunpowder works and chemical explosives factory in Cliffe Marshes. Established in 1892 by Hay Merricks & Co as a gunpowder works but subsequently developed as a cordite factory in the early 1900s by Curtis's and Harvey Ltd. The site was closed in the 1920s. A number of earthworks and building remains are still visible at the site.
The extensive remains of ruined buildings and earthworks of blast mounds around the explosives stores, support roads and numerous ponds have been mapped from aerial photographs and Environment Agency lidar imagery as part of the English Heritage: Hoo Peninsula Landscape Project.
The remains occupy and area 1km x 1.6km in the north-western corner of the Hoo Peninusla. The site was originally chosen because of the isolated location devoid of trees and some distance from settlement. The site is divided into different areas with distinctive plans and forms of building or structure. Some variation is as a result of development and expansion of the site from the initial core on the western side where cordite was manufactured, extending eastwards with time. Specific areas have been identified through extensive investigation and surveying of the site undertaken by English Heritage. A block of buildings on the southern edge of the works at TQ 7215 7830 has been identified as the acid factory.
The eastern half of the site is a later phase associated with the HMO Cordite Works. This part of the site is dominated by two areas of dispersed structures arranged in ordered grids linked by a grid of support roads which date from the First World War. The northern group centred at TQ 7253 7899 comprise 33 reinforced concrete buildings c.17.5m square which are sub-divided into 4 rooms occupying an area 590m x 295m which have been identified as cordite drying stoves. Extending down the eastern edge of this group of structures are 5 magazines surrounded by earthworks to contain any explosions. These were the last structures to be built on the site. There is the remains of a large area of cratering at TQ 7275 7874, perhaps where a 6th of these earthen banked magazines stood at the southern end. Along the southern edge were seven of long sub-divided reinforced concrete buildings, four of which remain. The western pair are 60m long, divided by a central spine wall, divided in 30 bays along either side. These are thought to have been used to store small amounts of explosives more unstable than cordite. East of these were another pair of ranges, originally divided into 9 bays.
To the south of this is an area of dispersed embanked structures centred at TQ 7272 7848 covering an area of c.305m x 325m. This comprises 6 rows of gun cotton drying stoves protected by thick earthen bank. Each forms a sub-rectangular structure c.23m 28m, each with an entrance in the south-western corner. They are spaced at about 30m intervals with service roads extending E-W between the rows, each road flanked to the south by a long water-filled pond.
The site is low-lying and prone to being water-logged, being former reclaimed marshland now protected by a considerable sea wall. The aerial photographs, lidar imagery and maps of the area revealed the earlier network of drainage ditches, many probably dating from the 18th and 19th century. Also visible are traces of more sinuous former creeks pre-dating the man-made drains.
The site is believed to have been utilised during the Second World War as a bombing decoy. However, no definite structures have been identified within the ruins of the explosives works. A row of posts has been noted on aerial photographs and during field surveying of the site which may have carried lights, but are almost certainly associated with the explosives works. Essentially, any of the existing structures on the site could have been utilised to create an extensive decoy settlement or factory complex. (1-6)
N.B. THIS MONUMENT RECORD SUPERSEDES DUPLICATE RECORD UID 1075508 / TQ 77 NW 121.
A copy of the General Descriptive Text from authority 1-1a of that previous record has been transcribed below under authority 8-8c. (7)
TRANSCRIBED FROM UID 1075508 (as 8-8c):
TQ 730 785. The Explosives Factory at Cliffe is situated about two kilometres to the northwest of the village of Cliffe on the south bank of the Thames. The factory began life as a Gunpowder Works, established in 1892 by Hay, Merricks and Company, gunpowder makers of Roslin, Scotland. It was a specialised Gunpowder Works engaged only in the finishing operations of gunpowder manufacture, namely blending, dusting and packing. A jetty was constructed to receive and dispatch powder and the original licence plan showed it was intended to construct 14 buildings. However, it appears that only two buildings were erected. An amending licence was issued and the site was used for the storage of explosives and electrical detonators, with a potential capacity of 400 tons. During the Great War Curtis's and Harvey at Cliffe was listed as a place where gunpowder was either manufactured or stored.
In 1898 the site was acquired by Curtis's and Harvey, gunpowder makers of Hounslow who by this date had a controlling interest in 50% of the British gunpowder industry. The flat, open and remote site at Cliffe was ideal for the construction of a new chemical explosives factory for the manufacture of nitroglycerine, and nitroglycerine based products. In June 1901 an amending licence was issued for the manufacture of cordite, blasting gelatine and gelatine dynamite. Further amending licences were granted as the factory expanded including one to manufacture the chlorate based explosive Cheddite. The later documented history of the factory is sketchy and no contemporary plan of the factory has been located. The eastern part of the factory is depicted on the 1908 Ordnance Survey map Kent IV.10, but does not show the functions of the individual buildings. Unfortunately the adjoining sheet to the west does not show the factory layout.
At the end of the Great War Curtis's and Harvey were absorbed into Explosives Trades Limited which later became Nobel Industries Limited. The Cliffe factory was, however, a victim of the sharp downturn in the explosives market at the end of the Great War and the factory closed in 1921.
Extensive remains of the factory survive on Cliffe Marshes with the potential to recover an almost complete plan of the works. The remains comprise earthworks of traverses and the lines of internal tramways, concrete floor slabs and a number of standing but roofless buildings. A row of concrete stanchions also survives on the site, which may represent the line of steam heating pipes or may be an element of a Second World War Bombing Decoy (TQ 77 NW 122).
The factory was approached on the landward side from Cliffe village along a lane ending at the Poplars (TQ 718 785). This group of buildings comprises the derelict remains of three single storied structures, probably representing the factory offices. Immediately to their northwest is an area of concrete floor slabs, their large size and the absence of protective traverses suggests they formed part of the acid factory. Another large area of concrete floor slabs to the southeast of The Poplars may represent another acids section or possibly the remains of a Guncotton Factory.
Returning to the area north of the Poplars the earthworks of a nitroglycerine factory may be identified, centred at (TQ 718 787). This is a distinctive form of monument comprising what may be identified as a nitrator at its southern end with a production flow which worked northwards. If this factory corresponds to a standard type the two circular traverses to either side of the nitrator might be expected to have held washing houses. The next set of traverses to their north might be interpreted as pouring on or mixing houses where the nitroglycerine was mixed with an inert solid. The traverses at the centre of the group might be a wash water settling house where any waste nitroglycerine was floated off the wash waters. A remarkable feature of this group of earthworks is the use of circular traverses around two of the buildings. This is an unusual form and is only known elsewhere at the Royal Gunpowder Factory at Waltham Abbey which might suggest that this plant was closely modelled on the one at Waltham Abbey.
To the north-east of the nitroglycerine factory are a series of long rectangular floor slabs, of building originally divided into bays which may represent cordite processing ranges. Surrounding these former buildings are large groups of earthwork traverses which formerly surrounded single buildings. Without more careful analysis it is difficult to ascribe functions to these buildings. They might be expected to have contained drying houses, storage magazines and process buildings for the mixing and packaging of explosives.
A large group of reinforced concrete stores or magazines and long rectangular buildings arranged in a subrectangular plan to the east suggests that the factory was considerably expanded during the Great War. At the centre of the new area were seven long, reinforced concrete structures, four of which remain. The westerly pair are 60m long, divided in two by a central spine wall, with 30 bays along either side. These very small bays suggests a design to handle small amounts of explosives far more sensitive than cordite. To their east are another pair of ranges, 51m in length, each was originally divided into nine bays. In a block between these and the Thames are 20 untraversed, reinforced concrete magazines or stores. Each measures 16m x 14m and is cruciform in plan, divided into four separate compartments. The sites of other groups of structures erected at this time are marked by concrete floor slabs or earthwork traverses, but it is not possible to say with any certainty whether they were associated with the manufacture of storage of explosives.
An octagonal brick traverse surrounded by a circular earthwork may also be associated with this group. The interpretation of this feature is difficult as it lies away from the main acid processing areas or nitroglycerine factory where explosives mixing might expected to have taken place. But is perhaps not sufficiently removed from the factory to be considered part of the Great War air defences of the factory.
(8-8c)
NB: THIS RECORD SUPERSEDES UID 1075508 / TQ 77 NW 121, AND HAS BEEN MADE THE PRIMARY REPOSITORY FOR ALL FURTHER UPDATES. The site had been mistakenly given two NRHE monument records.
Between November 2010 and January 2011 English Heritage’s Archaeological Survey & Investigation Team undertook a detailed 1:1000 survey of the factory remains, covering approximately 128 hectares of reclaimed estuarine marshland, as part of an in-depth analytical investigation of the form, function, condition and history of the factory site (Event uid 1583839) for the wider Hoo Peninsula Historic Landscape Project. The archaeological survey has recorded a surviving landscape of ruinous industrial building, building foundations, earthen traverses, tramway embankments, drains, and water-filled borrow-pits dating to the first two decades of the 20th century, around half of which represents a single episode of expansion in response to the munitions drive at the start of the First World War. In addition to the surviving elements of the early 20th-century landscape, a number of earlier land management features survive, such as drainage ridges and sheepfolds, as well as evidence of aerial target practice during the Second World War and agricultural reuse of factory features from the years following the factory’s closure. The survey drawing (the first meticulous and accurate plan of the whole site), investigation results and a detailed history of the factory have been published comprehensively as a lengthy two-volume report which is freely available through English Heritage’s online Research Report Series (9a); the report presents a level of detail and understanding far outstretching what was previously known about the site.
As described by previous authorities, the site’s association with explosives began in 1892 when Hay, Merricks & Co set up a small-scale gunpowder storage facility here. Then in 1898 the site was acquired by Curtis’s & Harvey Ltd who quickly established a new chemical explosives factory. The works grew rapidly, spreading out east and south across Cliffe Marshes from its origin at Lower Hope Point, with structures and tram networks being organically fitted in amongst the pre-existing drainage dykes. Two of the original gunpowder structures were incorporated and reused, evidenced on the ground and by comparing the 1897 and 1908 editions of the Ordnance Survey map (9b, 9c). In response to the demands of the First World War, in 1916 the factory became a government controlled establishment manufacturing a range of propellant and blasting explosives with a primary focus on producing naval cordite. As a result the large and regimented layout of a second cordite factory - HM Cordite Factory, Cliffe - was constructed immediately east of the existing works (which continued to manufacture a range of explosives), this saw the factory almost double in size. It was a short-lived enterprise and the whole factory closed around 1920 due to the post-war reduction in demand for munitions. Sales particulars prepared for the auction of the government-controlled portion of the site (9d) provide valuable about the construction and function of buildings relating to the wartime cordite factory, and have allowed for an accurate manufacturing process-flow to be understood for majority of the remains across the eastern side of the site. The precise function and relationships of buildings in the earlier western parts of the site are less certain, but the identity of many of the buildings have been recognised or proposed as a result of English Heritage’s detailed research.
Key to the importance of the site is its well-preserved plan form and layout which, virtually unchanged since closure, captures in its entirety the manufacturing process that occurred on the site and demonstrates the impact of both the influential time of change in the British explosives industry (from black powders to chemical explosives) and of the immense demand on armaments production caused by the First World War. The condition of individual features, however, is poor. The site was comprehensively stripped of all reusable materials at the time of closure, leaving only concrete and earthen remains and the occasional brick building. The unusual use of reinforced concrete (‘ferro-concrete’) as a building material, predominantly in the 1916 HM Cordite Factory expansions, is also key to the site’s importance. Most of the example are cordite drying stoves built in conjoined groups of four in quadrant arrangements in the north-eastern area of the site, but reinforced concrete has also been used to construct the long bayed ranges of two press houses (at TQ 7260 7868) and the partition walls between bays in the adjacent long ranges of acetone recovery stoves (at TQ 7242 7867); all these building are roofless. Reinforced concrete had a short-lived uptake in the explosives industry and these structures appear to be a unique survival of the material used in this context.
The Ordnance Survey grid reference given by authority 1 is slightly east of the actual footprint of the former explosives works; a more accurate central OS coordinate is TQ 7123 7870. The site is on land owned by the Port of London Authority and managed by tenant farmers. There is no public access.
(9, 9a-9d)
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