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Rhydymwyn Valley Works - North Wales - Oct 2010
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Arrow Rhydymwyn Valley Works - North Wales - Oct 2010 - 19-10-2010, 15:47

Valley Works
The Valley Works acquired itsí name in 1939 when the Ministry of Supply instructed ICIís Special Products Division to construct a factory and storage area in the Alyn Valley close to Rhydymwyn. The factory was to manufacture mustard gas. In the years 1940-1959 it was involved in 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 countryís stock of mustard gas. In the post-war years major quantities of lower grade mustard gas was prepared for sea dumping.
The Alyn Valley at Rhydymwyn has good road and rail links, water from mines and the Alwen Reservoir (Birkenhead Water) but not from the River Alyn which flows for only four months each year. There was also ample electricity from the North West Power Company's Hawarden sub-station. On one side of the valley has a limestone hill. The valley was also in a flood plain with a meandering river coursing the valley. It is 6 miles from the tidal Dee Estuary but close to the chemical/industrial complexes of Runcorn/Widnes/Warrington. The site was known as the 'secret factory' as it was the only second world war weapons factory never found or targeted by enemy aircraft. It was where a particular form of mustard gas called Runcol was made.

In this building, scientists carried out early research into the creation of the Atomic Bomb the project, known as Tube Alloys was top secret.

In this area, bombs were filled with explosive charge, fuses and pyrotechnics. It was the most dangerous job in the factory because of the risk of explosion.

The Tunnels were used to store the Mustard gas and Munitions created in the factory.

Thank you.
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Default 19-10-2010, 15:54

Nice report Whats the security like round this place?

smoke me a kipper ill be back for breakfast
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Post 19-10-2010, 16:18

Good stuff m8,ive heard a lot about this place over the years.
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Default 19-10-2010, 16:30

Originally Posted by buddah View Post
Nice report Whats the security like round this place?
Ask the nice men and he'll give the guided tour.

Good work, I went here a couple of years ago. We even got to see inside the tunnels, not very far though.
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Default 19-10-2010, 17:35

good work m8
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Default 19-10-2010, 19:37

A few of mine

This was one day that I would welcome a visit to the "Welsh National Museum of Warmth and Dryness"

Just a few odd pics.

One of two ( three actually - but two are parallel) long culverts that were used to divert the River Alyn from being a meandering stream to a culverted river, so that the works could be built.

The cross pieces are stone traps, but were reduced in height by some academic - and are now useless.

After some initial floods, capacity was increased by making another culverted (parallel) route (under the tunnels). The new route is on the right.

The pump used to extract water for the works (a well was also used when the river was not flowing).

Tunnel entrance

Tunnel Plan

The tunnels were split into 2 horizontally for ventilation and airflow


NO prize, but anyone guess what it is ?

Building P4


Power Distribution

Building "50" sign and remains of camouflage

Rhydymwyn works made poison gas, and charged armaments with it, during WW2.

This building is one of two magazines, both of which are several hundred yards apart, obviously for safety, and are more or less identical. Both are also cut into the hill on the west side of the site, both have blast walls, and both are raised well above the rest of the site.

This is a working party to start clearing the drains around the southerly magazine, as the standing water is damaging the structure.

Walkway between the two magazines. There is a deep open drain either side, a retaining wall, the pathway is covered (more or less totally intact) by soft ashphalt, to minimise sparks etc.

Entrance to the southern magazine:

Quick and easy WW2 structure, note the wood grain to the concrete, and peeling back ashphalt roof covering:

External Fusebox (for the fusebox enthusiast):

It's a good job the power is off:

From above - note the WW2 camouflage paint, still there:

Camouflage netting supports:

And inside - not a lot. Note the lighting - only accessible from outside,very light concrete trough roof, and the steam pipe for heating:

Last edited by n10694; 19-10-2010 at 19:40.
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Default 19-10-2010, 19:42

Originally Posted by buddah View Post
Nice report Whats the security like round this place?
Security is on the gate but he never left his cup of tea all the time I was in there. As EWJ commented you can phone for a tore of the place but that is not exploring to me. but it will get you in the tunnels.
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Default 19-10-2010, 20:01

Sorry to have to tell you but this is a giant bird box to encourage birds to nest thay were put here by the National trust, thay are all in front of the bird watchers hide. nothing to do with the base sorry to disappoint.
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Default Rhydymwyn - 02-11-2012, 20:01

This is only a mile or so from me, from what I remember around 1940 - 1942 heavy water research ( atom bomb) went on here. The scientists stayed in local lodgings but complained so a number of art deco odd looking detatched houses with port holes and flat roofs were constructed for them and there families. These houses are still with us and lived in, they are possibly grade 3 listed, the locals refer to them as 'The ICI houses". When the septic's entered the war (yanks) we gave them heavy water research ( they gave us some ships) and the scientist\s were all packed off to Los Alamos.

I was talking to someone about 10 years ago about either Olwyn Goch or Milwr tunnels and they told me the at some point one of them intersects with the Rhydymwyn tunnels. If this is the case they go further into the rock than we are led to believe.

When bomb fills used to get balls'd up and phosgene and other kacky stuff was spilt the duff shells were just burried in the ground. When we had the bad floosd about 11 years ago the site was under 5 feet of water. Portem Down were Kacking it and spent 4 weeks on site doing soil sampling but stated nothing horrible was detected. It's obviously still not right hence full time security, nce new fences and lots of hitech CCTV

Good stuff

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Default 02-11-2012, 23:51

there was water pumped out of the milwr to this place, i have no idea if you can actually make a trip from this place into the milwr tunnel, but there was deffo a connecting pipe

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