Scope and Content

Ministry of Defence Records. Contents include correspondence regarding the site and facilities within it; minutes of site meetings; drawings, plans and aerial photographs of the site, buildings within it and services between and within those buildings; site inventories, 1940 and 1960.

Administrative / Biographical History

The M.S. Factory, Valley was a Second World War site in the United Kingdom that was used for the storage and production of mustard gas. It was later also used in the development of the UK's atomic bomb project. More recently, it became a bulk storage depot for emergency supplies. The site occupies around 35 hectares of the Alyn Valley, to the south of the village of Rhydymwyn.

In the late 1930s the Chamberlain Government planned that the United Kingdom should be in a position at the beginning of any war to retaliate in kind if the Germans, as expected, utilised mustard gas. In April/June 1939 the Alyn Valley was surveyed by the Department of Industrial Planning on behalf of the Ministry of Supply (MoS), and Imperial Chemical Industries (ICI) who were tasked with managing this programme. The land was purchased by the Ministry of Supply for development as a purpose built chemical weapons factory and storage facility. The Treasury approved the sum of £546,000 for initial work on 27 August 1939; and work began in October 1939 on the storage tunnels, in the limestone hillside. The factory, to be called M.S. Factory, Valley, opened in 1941. The government authorised the expenditure of £3,161,671 and ICI's construction fee was £80,000. Over 100 specialised buildings were constructed across the site, linked by an extensive rail network established around a spur off the Chester to Denbigh mainline. Other major landscaping undertaken at this time included the canalisation and culverting of the River Alyn, and the excavation of a complex of interlinked subterranean, rock-cut tunnels and caverns.

In the years 1940-1959, it was involved in either the manufacturing, assembly or storage of chemical weapons, or mustard gas in bulk containers. During the years 1947-1959 the tunnel complex held the majority of the country's stock of mustard gas. Production was intended of both Runcol and Pyro variants of mustard, however, records reveal that only the purer and more stable Runcol was made in bulk.

On accepting the findings of the Maud Report in 1941, the government of the day needed to verify that a cost effective atomic bomb could be manufactured. This required verification that a gaseous diffusion process would work on an industrial scale to provide enough fissile material to manufacture a cost effective and timely Atomic Bomb. One of the surplus Pyro buildings at Valley (P6) was adapted for the testing of apparatus for uranium isotope separation in 1942 in an early phase of the ‘Tube Alloys’ project before this was moved to America (developing later into the Manhattan Project). Four prototype gaseous diffusion plants were ordered from Metropolitan Vickers, at Trafford Park, Manchester at a cost of £150,000 and installed in the P6 building at Valley. Test equipment was installed in the P6 building at Valley and experiments continued until 1945 when the equipment was moved to Didcot and Harwell. The results of the experiments led to the building of the gaseous diffusion factory at Capenhurst, Cheshire. Building P6 is now a Grade II listed building and is of international importance; for a very brief period it was at the leading edge of nuclear physics.

In the immediate Post-War period the site was used to store German nerve gas, and it was not until the 1950s when Britain relinquished its chemical weapons (CW) capability that the site as a chemical storage facility was defunct. However, the site remains on the international Chemical Weapons List, and is still monitored as such.

During the Cold War, as a result of Great Britain's previous experiences of the U-Boat blockade during both World Wars, and disruption to transport communications as a result of aerial bombardment during World war II, the government decided to set up a system of food and raw material stockpiles to counter the threats of a nuclear war. These stores were mostly based on the reuse of existing government-owned sites and buildings; and the former M. S. Factory, Valley was adapted to became one of these storage sites. It became a bulk storage depot for emergency supplies. From the mid-1960s the site was used by various governmental departments, its major function being a buffer storage depot to supply emergency rations and foodstuffs, and associated facilities such as mobile bakeries and canteens. In 1994 the site was finally closed, and a programme of demolition was undertaken. This involved the dropping of buildings onto their footprints, and the rubble being mounded over with topsoil. However, several major structures, and many ancillary buildings, still survive across the site.

Research has shown that whilst the attrition rate of certain building types has been quite high across the site, the fact remains that there is no other CW production, storage and assembly site surviving within the UK in such a complete and readily understandable state. This makes the Valley Site as a whole a place of national significance, but of particular rarity and importance are the surviving production buildings, which are, as far as can be ascertained, unique survivals.

Recent disclosures in TNA documents identify that the tunnels at the former Valley Works at Rhydymwyn were planned to be used in the Cold War for the relocation of the 3,700 tons of gold from the Bank of England vault at Mount Pleasant. This transfer would have taken place in the run up to war and would have been effected by soldiers in 10 ton lorries. The transfer would have taken 10-14 days and the unpacked gold bars would have been unloaded and stacked by forklift. The soldiers would then have used 6,000 square feet of surface accommodation and guarded the site. This operation, originally named MALLARD, was later called FOLIUM. This arrangement was still in place in 1980 [source: Colin Barber, Rhydymwyn Valley History Society].


Arranged into the following: Minutes, Inventories and Registers, Reports, Technical Reports, Correspondence, Memos, Signing Off Papers, Site Plans, and Aerial Photographs.

Access Information

None. These records were classified as secret but this has been rescinded by the MOD.


Please order documents using the alternative reference number (where provided).

Other Finding Aids

A hard copy of the catalogue is available in Flintshire Record Office.

Archivist's Note

Compiled by Steven Davies for the ANW project.

Conditions Governing Use

Crown Copyright. Usual Restrictions Apply.

Appraisal Information

All records received at Flintshire Record Office have been retained.


Further accruals are expected.

Related Material

D/DM/1678 - Rhydymwyn Valley History Society Records

Geographical Names