Ancient Monuments

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Ministry of Supply Valley Site

A Scheduled Monument in Gwernaffield with Pantymwyn (Gwernaffield gyda Pantymwyn), Flintshire (Sir y Fflint)

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Latitude: 53.1855 / 53°11'7"N

Longitude: -3.1891 / 3°11'20"W

OS Eastings: 320639

OS Northings: 366040

OS Grid: SJ206660

Mapcode National: GBR 6X.3CTY

Mapcode Global: WH774.Z6K7

Entry Name: Ministry of Supply Valley Site

Scheduled Date: 10 September 2008

Source: Cadw

Source ID: 1249

Cadw Legacy ID: FL210

Schedule Class: Defence

Category: Ordnance factory

Period: Post Medieval/Modern

County: Flintshire (Sir y Fflint)

Community: Gwernaffield with Pantymwyn (Gwernaffield gyda Pantymwyn)

Traditional County: Flintshire


The monument comprises the remains of underground caverns and a group of twenty-one munition assembly buildings in the Danger Area at the Ministry of Supply Valley Site. The caverns were designed to provide secure, bombproof storage for the Government's reserve stocks of chemical weapons. Buildings were provided for the filling of munitions and the manufacture of vesicants. The factory was located on the narrow valley floor of the River Alyn to the S of Rhydymwyn. Building work commenced in late 1939 and buildings were commissioned for use from late 1940. The caverns comprised three parallel tunnels driven 250m into the western hillside, which accessed four transverse storage galleries. The terminus of each outer tunnel was connected via a ventilation shaft to a chimney, now demolished, on the hillside. Subsequently, three of the galleries were lengthened or widened. The surviving buildings in the Danger Area were involved with the assembly, packing and storage of chemical weapons. They also included buildings relating to welfare, emergency and personnel functions. The Danger Area buildings were interconnected via clearways surfaced with special asphalt designed to minimise contamination. Production at the site ceased in April 1945 and decontamination and disassembly began in 1948. During the Cold War, the tunnels were used as a buffer storage depot for emergency rations, bakeries and canteens.

The monument is of national importance for its potential to enhance our knowledge of British WWII chemical weapons production, where there is a very limited survival of evidence overall. The Danger Area buildings were built to designs adapted for chemical weapons work and are a unique survival in the UK. The survival of the plan form and layout of the storage caverns and buildings demonstrates the industrial processes at the site. Together the structures form a readily understandable group and possess important group value. The remains of the individual structures are well preserved and retain significant archaeological potential, with a strong probability of the presence of associated archaeological features and deposits.

The scheduled areas comprise the remains described and areas around them within which related evidence may be expected to survive. Area A is centred on Item A at SJ 20540 66110. It is roughly rectangular in shape and measures 300m NE-SW by 280m transversely. Area B includes Items B-V and is centred on SJ 20950 65850. It is an irregular polygon in shape and measures 360m NW-SE by 140m transversely.

Source: Cadw

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