Royal Marines have entered a vast underground complex beneath a Wiltshire town for a training exercise.

Royal Marines from Juliet Company of Plymouth-based 42 Commando work in small teams on Royal Navy warships and they are also the home of the Fleet Contingency Troop (FCT) – experts in a range of security missions and the UK’s only force trained in opposed boarding operations (known as Level 3 (Opposed)) outside of Special Forces.

The Ministry of Defence say that the FCT have been training in the subterranean world of Corsham Tunnels, below the town of Corsham near Bath.

“The complex of tunnels became a facility for the potential relocation of the government in times of crisis during the 1950s with the threat of nuclear war looming large. These days, parts of it are a useful training area; a place where the commandos can push themselves in the art of close-quarters combat, testing their well-rehearsed tactics, techniques and procedures to quickly assess and deal with threats in even the trickiest of environments.

This is all ahead of deployment to the Mediterranean to join their 42 Commando comrades from Support Company – plus elements from 40 Commando, 47 Commando and 30 Commando IX – as the future of commando forces is shaped on the Littoral Response Group (Experimentation) deployment this autumn.”

The MoD add in a news release that this is all ahead of deployment to the Mediterranean to join their 42 Commando comrades from Support Company – plus elements from 40 Commando, 47 Commando and 30 Commando IX – as the future of commando forces is shaped on the Littoral Response Group (Experimentation) deployment this autumn.

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I worked with the RM Green team as part of the RN Blue team doing boardings in the Northern Gulf Post GW 2. Rapid roping out of Helos, abseiling down container stacks, searching all sorts of vessels it was a great experience.
I learnt a lot from them and even got to play along on a few opposed boarding exercises. Not sure if I helped or hindered but I wouldn’t want to be on the receiving end of an opposed boarding. They really do not mess about as the OpForce USN Seals found out!

Daniele Mandelli

That complex is huge. Only a part of it was / is a “Nuclear bunker”, most is the remnants of the Beaverbrook aircraft factory in various quarries. There was rail access at the eastern end of Box Tunnel.


It was abandoned as a war hq in the ’60’s when the increased accuracy of ICBMs made it a siting target, though it was kept going as a possible rebuilding centre in the case of war, though obviously not fully manned in peacetime. It also had simulated comms traffic to make it seem it was still the hq. In reality reconstruction teams were to be dispersed all over the UK, including on Calmac ferries in Scotland – Project Ruby, among many names.. Overflown on a regular basis by Soviet satellites.

Daniele Mandelli

Thats right HF. I was a Sub Brit member, so aware of the CGWHQ in Spring Quarry. Burlington, Turnstile, Chanticlere, or in later times, Site 3.
Although the government would disperse to RSGs around the country, until 2003 I think it was kept on a C&M basis. And ironically, despite the accuracy of ICBMs, there are other sites there with command functions to this day, ISS, GOSCC and the facility in District 9 foremost amongst them. The CGWHQ actually sits beneath the ISS site.


There’s a cold war group on facebook you might find interesting:- BRITAIN’S COLD WAR

Daniele Mandelli

Thanks, will have a peep.


CAD (Central Ammo Depot) that’s why the train was there. Strategy was to create resilience in the supply chain and likely somewhere to fight from should the invasion of Britain begin. They sunk alot of money in it to keep dry. Then they started to build the various usages in the cold war, as then, like America it was thought that a load of concrete and a deep hole would ensure the State carried on; until they realised how much of a hole the USSR was going to make and that there wouldn’t be any taxes to pay for MP… Read more »

Daniele Mandelli

Thats right. Other parts of CAD are at Monkton Farleigh.

At least the US has mountains to dig under. We are more challenged in potential sites for really deep sites, unless we use old quarries and mines like at Blanaeu.

Andy P

Plenty hoofing big hills to burrow under up north Daniele. Maybe not that discrete now right enough. Much as I love this stuff and have worked down some of the UK ‘holes’, you just have to hope they’re not needed.

Daniele Mandelli

Indeed Andy P. As long as we keep some and don’t turn them into museums.

Graham Moore

My concern is that we precipitously dismantled the UKWMO, ROC and abandoned/sold off most ‘underground bunkers’ for military C2 and RSGs within a few short years following the collapse of the Soviet Union.
If a similar existential threat emerged to the homeland, we would struggle to have any resilience at all.
Also, National Home Defence was possibly last seriously practised by ‘above ground’ forces in Ex Brave Defender in the mid-80s.

Daniele Mandelli

Yes, I agree. The costs of recreating them would be horrendous. Most “known” ones were sold off, yes, but especially on the RSG civil side. I’ve always suspected there are some underground sites on the MoD / Intel side that are still classified kept for a rainy day, so not all is lost IMO. The RSGs were busted by Spies For Peace and other whistelblowers. I’ve read that places like Kelvedon Hatch and Anstruther, which are now museums, have clauses allowing their requisition by HMG in need. I don’t know the truth of that though. Other RSG are now used… Read more »


I used to lead tours round the CAD. Amazing place – tier after tier of storage areas for munitions; barrack area and train station still there (I believe).

David Barry

What happened to Broughton Moor (RN Ammo) in near Flimby, Cumbria? Was that not a tad deep?

J t robinson

Is interesting.former younger marine cadet now past sell by date.