Site Records

This article was added to the Sub Brit web site in early 1997. Ian Davies is a pseudonym. Sources have not been cited and the accuracy of this article has been called into question by other researchers.

[RL 25/02/2008]

Rhydymwyn: History

By Ian Davies

This article gives a history of one of the UK's most secret underground sites. All of this information has come from documents which, although not necessarily in the public domain, are unclassified.

The Alyn valley in North Wales has been used by the UK government for storage of sensitive material for most of this century. The geology of the area is extremely useful - there is a layer of extremely pure, and hence structurally sound, limestone at depths ranging from surface to 900 feet. The layer is anything up to 200 feet thick, and is riddled with lead and zinc mine workings and drainage tunnels. Added to these ready-dug tunnels, there is a very low population density around the mining sites, and yet remarkably good transport links. The Rhydymwyn area had wartime links to the LMS railway and the old A541, water from the river Alyn and cheap electricity. A system was devised to ensure a constant supply of fresh water to the site.

The Valley Works in Rhydymwyn, north of Mold in Clwyd, has a chequered history. The site was originally used for mining, but due to market changes was rapidly considered commercially unviable. At this point, the government gained control of the site.

In 1937, the UK War Ministry looked at the potential use of chemical weapons, and in 1938 the Valley Works (known to staff as the Foundry) was selected as the UK site for production and storage. This was followed in 1939 by the storage of over 10,000 tons of TNT in interconnected workings at Hendre. In September 1938 the Ministry of Supply started construction of a purpose-built chemical weapons storage facility. Incoming services were adequate, however waste disposal was difficult, and a 24 inch waste pipe was laid in total secrecy the six miles to the Dee estuary for the disposal of high level waste. Arrangements for gaseous emissions were classified as an ``acceptable risk to the local populous''.

The early work

The four tunnels were fitted with blast doors, and two led to a set of air shafts that emerged at Twmpath. The storage capacity during 1941 was in excess of 3120 tons in forty-eight 65-ton steel and lead tanks in two of the chambers, plus 2000+ tons of charged munitions in the others. The complex used four 2-ton underground cranes to handle the munitions. In addition to this, an overflow store at a nearby location, codename `Woodside', has capacity for 2090 tons.

The tunnelling process involved 2200 miners and `company security' officers. The miners were told that they were preparing a set of storage tunnels for `national art treasures'. In reality, they were not completely deceived as these were indeed stored in Clwyd, but at the Grange site, some miles to the north.

The original batch of chemicals arrived on 19th June 1940 from the ICI production facility and stored on the surface at a location codenamed `Antelope'. They arrived by road and rail, the road convoys were made up of a tractor/trailer unit, a decontamination vehicle, and a police escort. All transports into and out of Valley had joint army and police escorts and a decontamination unit, not identified by the usual livery. The stockpile at Antelope was buried with a foot of soil and remained there until September 1941 while the handling systems were installed at Valley and Woodside. At that time, Woodside's storage tanks were installed, and the twenty 55-ton lead-lined tanks held runcol (the blistering agent used in mustard gas), 21.5 feet under the surface.

This offered minimal protection, and considering the Mold area had over 1000 air raid warnings in 1940 - 45, it is remarkable that no damage was ever inflicted to either complex. Valley (and more specifically Woodside) is the only UK wartime installation that was never located by German intelligence. Neither officially exists, even today. During the war, passing any intelligence on Valley to any member of the public, of either nationality, was a capital offence.

In January 1942, staff from ICI Randle arrived to supervise the startup of the Valley production plant. There were numerous `teething troubles', including several blow-outs from ventilation systems that exposed local residents to dangerous levels of constituent chemicals. The management of the site was instructed to ensure by all means that nobody tried to sue the site in case intelligence of the reported symptoms crossed to the enemy. Workers used CBS protection and barrier creams, and emergency washdown systems were built around the plant. During 1941 - 1945 there were 930 accidents, 20 percent of which were rated as `VS/F', either `very severe' or `fatal'. The number of fatalities caused by Valley to the staff and residents is not officially recorded.

Munitions arrived from the start of 1941 and by the end of March the payroll lists 262 workers. Production peaked in November 1942 when over 40,000 25-lb shells were being filled every week. From April 1942 until 1945 Valley received 5,000,000 units and filled 4,720,000, plus 1,420,000 smoke-generating devices.

In 1942, after a series of incidents with leaky 65-lb devices, a dramatic drop in the worker's health (including some fatalities) forced the ICI supervisors to restrict toxic workers to a 48-hour week. `Toxic handling' staff peaked at 406 (79 of them female) on 1st November 1942. By 1945 there were only 30 left. The total staff varied during the war from 929 at the end of March 1942 , to 1756 in September, and falling to 1217 by March 1944. 160 of these were surface-based lab staff, and 120 of these were based on non-chemical work - declassified very recently as the UK atomic weapons research programme.

Chemical handling was, by modern standards, extremely poor. Waste removal was the most dangerous listed task at the site. Small items were incinerated, or boiled in soda ash. The residue was pumped along the 24-inch pipe to the Dee. The level of contamination in the estuary during the war years was categorised as `serious'. Anything impossible to boil or burn was packed in bleach and stored in disposal pits. When these filled with water, workers had to hand-pump the pits to stop dangerous buildups of fumes, in scenes reminiscent of Chernobyl.

By the end of January 1945 the plant had made 15,477 tons of runcol, and stored several thousand gallons of acid for mustard gas production. All chemical weapons production ceased on 29th April 1945. From 1942 to 1944 the work to separate and process uranium-235 was based at the plant.

Shift in activity

In 1947, as the communist threat developed, Valley was again classified as the UK primary chemical store. The blast protection was upgraded because of the nuclear strike threat, and the surface site was redesigned. Security was seemingly low-key, and the official use of the plant remained as `rubber research'. Guards at the site were rehoused to ensure the public could not identify the uniforms. Concrete blast covers were built over the storage chambers. In 1952 the plans show 78 chemical storage tanks.

In 1952, the official policy of the UK shifted to nuclear deterrence, and the chemical stockpile was again disposed of, either at ICI Randle as part of `Operation Sandcastle'. The clearing process continued sporadically until in the late 1960s when the manifests show the site was clear.

Another shift

In 1968, civil defence was again downsized and Valley was classified `care and maintenance: most secure site'. In 1972, the MoD established regional HQs for all areas of the UK, however there was no such facility in North Wales in order to ensure no attention was attracted to Valley. In 1981 the DoE privatised all government services to Serco, with the sole exceptions of Parliament, Hawthorn and Valley. These three came under the control of the Property Services Agency (PSA). This controlled a number of other sites across the UK, all listed as `supply depots'. Valley was uniquely listed in the plans manifest as ``Special Site : Hawthorn National Complex''.

A programme on the industry of the Alyn valley by HTV in 1982 became a threat to Valley. They reported that areas of the land around the Rhydymwyn village were empty of industry and farming. The DTI quickly published a response that the sites were ``prone to flooding'', which is indeed true of several areas in the valley, but HTV pried further. This resulted in a response from the PSA (the first public response from the agency) stating that there were stockpiles of food and `office equipment' stored on the site by the then Ministry of Agriculture, as a wartime reserve known as a `buffer depot'. The PSA also stated that the site was being cleared. The visible portions of the original chemical plant air shafts were re-engineered in 1990.

Valley is now controlled by the PSA (now called Property Holdings) and MAFF.

In 2001 Sub Brit was given unrestricted access to view and photograph this site: see the visit report.

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