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It is a large military site and is situated north of the A48 road five miles (8 km) west of Chepstow and 12 miles (19 km) east of Newport. Since 1993 it has been used for a variety of military and civil purposes, including field exercises, car rallying, storage and breakdown of railway vehicles, nature preservation, and playing Airsoft. The site has its own standard gauge railway system (no longer linked to the national network), many private roads and a wide range of buildings, from small earth-banked stores to large four storey lightly built brick buildings. It is about two miles (3 km) east-west, and 1.5 miles (2.4 km) north-south. The perimeter road inside the security fence is, on its own, over seven miles (11 km) long.
1939 to 1965
The site was created as a Royal Navy propellants factory in 1939.
Note: The Royal Navy Propellant Factory, Caerwent, like the Royal Navy Cordite Factory, Holton Heath, was never part of the Ministry of Supply/Royal Ordnance Factory management chain; they were controlled by the Admiralty. However, they were functionally very similar to Explosive ROFs.
In the summer of 1936 the site requirements for a new factory were drawn up. The main priorities were:
- the establishment should not be vulnerable to air attack;
- should not be located in an industrial area, but sufficiently close to a populated area to provide an adequate workforce;
- should be close to a railway and to main roads;
- should be located on rough grassland with a gravel on sand subsoil with good natural drainage and a slope of about 1 in 30 to provide maximum safety in the highly dangerous nitroglycerine manufacturing and handling areas;
- the higher part should not have an elevation of not less than 100 ft (30 m) above the lowest part to limit the internal gradients.
Like all explosive factories of this type, a capacious supply of water was required for use in the manufacturing processes. To manufacture 150 tons of cordite per week the factory would need 3 million imperial gallons (14,000 m³) of drinking quality water per day.
In the final quarter of 19th century, the Great Western Railway (GWR) had undertaken the engineering feat of constructing the Severn Tunnel under the River Severn. One of the major difficulties encountered underground was the 'Great Spring', which necessitated the pumping of over 9 million gallons (41,000 m³) of water per day, at Sudbrook, from the western end of the tunnel, conveniently located only three miles (5 km) away from the proposed site at Caerwent. Even during the great drought of 1934 the lowest daily return was 9.1 million imperial gallons (41,000 m³). The GWR used about 1.5 million imperial gallons (6,800 m³) per day themselves, so there was always a guaranteed daily surplus of 7.5 million imperial gallons (34,000 m³).
The total area acquired was 1,580 acres (6.4 km2) of land, a total of 1,163 acres (4.71 km2) were enclosed within the factory fence. It was connected to the Great Western railway at Caldicot Junction, near Sudbrook by way of a private branch line, sometimes known as the MoD Caerwent sidings; and a number of transfer sidings were laid out inside the factory fence.
The site consumed the village of Dinham which was located at the northern edge of the RNPF Caerwent.
By the end of 1940 the Main Office block was complete, and in December of that year the Unit 1 Sulphuric Acid Factory went into production with acid mixing for the Nitrocellulose and Nitroglycerine manufacturing. Five months later, the Pressure Oxidation Plant for the manufacture of Nitric acid came on stream. In August 1941 the Nitrocellulose and Nitroglycerine plants were operational and were soon working 24 hours a day on a three-shift pattern. At the same time, Unit 2 of the factory was almost completed, so RNPF Caerwent was now virtually operational.
A total of £4.7 million was spent on buildings and roads, and £2.5 million on plant and equipment.
From 1955 to 1966, Caerwent produced the Gosling solid rocket booster for the Seaslug missile. This work began in wartime buildings, the horizontal presses in Press Houses 3 and a longer press in 1, and with other work in a disused blending house and the Tetryl Acetone Recovery building. From 1957 dedicated buildings, J1...J6, were constructed on the eastern side of the site for the production of guided weapons propellants. Buildings J7...J9 at the northern edge of the site formed a static testing site, where these motors could be test-fired. J7 was an environmental conditioning building where charges could be heated to 70°C or cooled to -40°C before testing. These buildings were of typical flat-roofed red brick construction, shielded by large earth traverses. Testing work was also carried out here on the Magpie, Redtop and Sealyham rocket motors.
Early in the 1960s a Parliamentary working party recommended that propellants for the three branches of the armed services should be concentrated at the Royal Ordnance Factory at Bishopton. The decision to close RNPF Caerwent was announced on 25 March 1965. Production continued during the following two-year rundown phase. The last Gosling motor was produced in 14 June 1966, tooling then being transferred to Bishopston.
RAF Caerwent - weapons storage 1967-1993
RAF Caerwent was transferred to US administration after Charles de Gaulle expelled the US military from France in 1967. Caerwent thus became part of the US Army European 'theatre reserve stocks' under the command of the United States Army's "47th Area Support Group Reserve Storage Activity", and became known as USADA Caerwent (United States Arms Depot Activity - Caerwent) with a Royal Air Force Liaison Party also present.
The US Army spent over £4 million constructing 300 magazines and converting some of the former RNPF structures to conform to the required specification. The material stored included small arms ammunition, artillery shells (up to 8"), anti-tank mines, grenades, flares, and the multiple launch rocket system.
The first shipments of shells, rockets, mines, flares and small arms ammo arrived early in 1968 with shipments arriving in lorry convoys as well as rail. The majority of lorry convoys took place at night not to cause local road disruption, along with the freight trains, as they had to fit with BR timetables. In the early 1960s Severn Tunnel locomotive depot was not far away and steam locomotive no. 2231 was allocated as a permanent locomotive for shunting etc. at Caerwent (Dinham). This locomotive had a special spark arrestor fitted in the smoke box at Swindon to avoid sparks being blown and causing a fire hazard. The driver and fireman were forbidden to smoke at any time whilst inside the perimeter gate. Maintenance facilities were added in 1971.
In the early 1970s the site's capacity was expanded substantially, which allowed the closure of three other munitions bases in the West Midlands (Bramshall, Ditton Priors and RAF Fauld) in 1973. One of the reasons Caerwent was retained was its proximity to Barry Docks where many of the armaments entered the United Kingdom.
At this time there was also an increase of US army staff, with many of them stationed at Caerwent for a short period of time after serving in Germany and prior to returning home stateside. There were also parties, film shows in the on-site cinema and barbecues were held for the families of local people to show them appreciation for working with the US army.
At its height Caerwent was among the larger ammunition supply depots in Western Europe, storing over 80,000 tonnes of conventional munitions, a substantial fraction of the US Army's European stocks. In 1990 Caerwent shipped 12,000 tons of ammunition to the Middle East and played a critical part in Operation Desert Shield and Desert Storm.
Following the change in the political climate in Europe and subsequent scaling down of operations, the US Army announced it was to close down their storage operations at the establishment in June 1992. Over 60,000 tonnes of munitions were moved out over a period of less than ten months. The last batch was removed by train on 19 July 1993. The formal closure ceremony took place on 20 August 1993.
The base is now maintained by a small army staff as a 'Training Area' for troops from Beachley Barracks and further afield. A 'representative sample' of the bomb storage and processing structures of this vast site can now be seen on the latest Ordnance Survey map showing roughly 200 structures. Previous editions showed the site as completely blank, but serviced by a railway line.
Caerwent is now a major training area covering over 1,500 acres (6.1 km2), capable of sustaining up to 1,000 troops. There are not only over 400 buildings and bunkers on the site, but also an operating railway (removed 2005-2006) and a comprehensive road system, for logistics exercises and driver training.
The site has been used for military training and public order training by various police forces. Local farmers are allowed to graze their livestock on the convenient areas of pasture that separate the former factory buildings.
Parts of the site have also been let for civilian usage, including driver training and car rallying run by Forresters Car Club and South Wales Automobile Club. Part of the site is also used by an airsoft club, under the name Dragon Valley The relay races of the 2007 JK Orienteering Festival were held on the site.
Since the privatisation of British Rail, RNPF Caerwent like a number of other MOD sites with internal railway sidings, has been used as a secure storage area for holding surplus locomotives and rolling stock that might be returned to use. A small number of electric locomotives, particularly in the British Rail Class 86 and British Rail Class 87, have been scrapped at RNPF Caerwent; also, British Rail Mark 2 carriages.
In 1995 the site was used in the Channel4 programme Scrapheap Challenge series, utilising the railway scrap yard facilities to create electric, diesel and steam powered railway locomotives. Scenes from two episodes of science fiction television series Torchwood were also filmed on the base, as were scenes in the 2006 film Big Nothing, starring David Schwimmer and Simon Pegg. Scenes from the Hollywood blockbuster Captain America: The First Avenger were filmed on site in October 2010. More recently, Caerwent was used in the television series Top Gear.
- Walker (1888).
- Walker (1888), Chapter 10: "The Means Taken to Deal with the Great Spring".
- R A Cooke (1985). Section 36: Ross, Monmouth and Chepstow. Track Layout Diagrams of the GWR and BR WR (2nd ed.). pp. 1–2.
- Jon Berry (November 2011). "Desperately seeking Sea Slug". Context. Cadw (122).
- "Caerwent is scene for Captain America movie". South Wales Argus. 28 July 2011. Retrieved 28 July 2011.
- Bowditch, M.R. and Hayward, L., (1996). A pictorial record of the Royal Naval Cordite Factory, Holton Heath. Wareham: Finial Publishing. ISBN 1-900467-01-1.
- Cocroft, Wayne D., (2000). Dangerous Energy: The archaeology of gunpowder and military explosives manufacture. Swindon: English Heritage. ISBN 1-85074-718-0.
- Walker, Thomas A.,  (2004). The Severn Tunnel: Its Construction & Difficulties: 1872 - 1887. Republished 2004. Stroud: Nonsuch Publishing. ISBN 1-84588-000-5
- 'The Factory' A history of the Royal Navy Propellant Factory, Caerwent by Medwyn Parry
- Subterranea site visit with photograph
- Multimap map and aerial imagery
- Aerial photograph 1999
- Orienteering map 2007