For years the secrecy surrounding the Rhydymwyn Valley Site served only to fuel rumour about what, if anything, could still be hidden in underground tunnels that once housed thousands of mustard gas shells during the height of production in the war years. And speculation has been rife for the last few decades since it was revealed that the works somehow played a role in the research into the first atomic bomb.

But in May 2006, specialists from Birmingham University who surveyed the site, released their findings saying there were no more secrets lying hidden in the underground tunnels, writes Nick Bourne from the webteam. In fact, the tunnels were completely empty.

However, they did uncover some interesting archaeological finds going back hundreds of years after being charged by the present owners - government department DEFRA - with helping to provide a greater understanding of the site's history.

They found that the site had been used from the mid 1700s for a range of industries which left behind remains of foundries, waterwheels as well as mine workings. In turn, this led to the building of a main road and a railway in the 1800s which made it a prime site by the time Winston Churchill called on chemicals manufacturer ICI to find a secret location to begin production of chemical weapons.

ICI suggested Rhydymwyn, said the experts, because it was 30 miles away from its production hub in Runcorn, Cheshire; the amentities, including a natural water source and transport infrastructure was in place; and because it was inland and relatively safe from air attack because the site was in a valley, heavily wooded and, from the air, looked no different from other nearby valleys.

So what did happen on the site? Production rooms were constructed to make mustard gas but, said the experts, this didn't happen. Instead, mustard gas shells were made on-site with all the components brought together to make the shells and bombs.

And what about the part the plant played in the creation of the first atomic bomb?

Well, apparently, leading experts were sent to the site by Churchill to follow up on a scientific research paper that showed how, in theory, a massive explosion - a chain reaction of explosions fractions of a second apart - could be triggered by splitting and using components of a certain chemical. Those same experts went on to play key roles in the US in the Manhattan Project, which developed the first atomic bomb.

Today, the site is considered historically important and in summer 2008 some of the uninspiring brick buildings were given protected status by Welsh heritage society, CADW.

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