History

For full history and analysis of the site and an explanation of the chemical processes see the Birmingham Archaeology report cited below.
The Ministry of Supply Valley Works, Rhydymwyn was built to produce mustard gas for military purposes, and to assemble, charge, and store chemical weapons. Important research took place here in the early development of atomic weapons.
In response to the use by Germany of poison gas in the First World War, Britain developed chemical warfare capacity. As war threatened again in the later 1930s, the Government, in association with industry, developed a series of new plants. Work at MS Valley began in 1939, and the site became operational in 1942. It continued to produce mustard gas until the end of the War. The works were run by ICI on behalf of the Ministry of Supply. After the War, stocks were gradually decommissioned.
The works was developed on a large site with distinct zones for production of mustard products, filling of shells and bombs, arming the weapons, and storage in tunnels in the hillside, as well as laboratories and administration areas.
Three plants were built to produce the Pyro variant of mustard gas and and two plants to produce the Runcol variant. Although two of the Pyro plants were commissioned they never went into full production. The third Pyro building was used for research in connection with the enrichment of uranium.
This building, P4 (as well as P5 and P6) was intended to house plant for the production of Pyro mustard, a less stable variant. However, as the threat of invasion receded, none of the buildings was used for production. P5 was used to refine Pyro mustard produced at other factories. Building P4 was a fully-operational back-up plant.

Exterior

A very large building of reinforced concrete frame construction with infill of red brickwork laid in English bond. Seven bays to long (east and west) elevations; on lower level of W elevation each bay formerly had 2 openings (ie 14 in all) now blocked.
The central section of 5 bays has segmental concrete vault over each bay. At each end a bay with flat roof. The N & S elevations have six bays externally. Square concrete tower to N over second bay from W. Much alteration and blocking of original openings. In S elevations, later insertions of two large vehicle entrances.

Interior

The interior is articulated by reinforced concrete posts; some circular openings to roof. Overhead rails for lifting gear. Building is divided longitudinally into 2 areas; to W the toxic area of 3 bays, and to E the non-toxic area of 2 wider bays.
At N end of non-toxic side, small single-storey divisions for two transformers and switch room. Remains of switchgear and fire-fighting equipment.

Reasons for Listing

As part of a group of buildings, which along with the Scheduled buildings in the Danger Area and the Scheduled storage tunnels [FL210(FLT)] illustrate the industrial processes behind chemical weapons production to an extent unique in the UK. Group value with the other listed buildings on the site.

External Links

• Cadwr Listing
• Wikidata Q29508092

External links are from the relevant listing authority and, where applicable, Wikidata. Wikidata IDs may be related buildings as well as this specific building. If you want to add or update a link, you will need to do so by editing the Wikidata entry.

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