When East-West relations thawed after the fall of communism, military installations like this one in southern England became surplus to requirements.
Today, despite fresh tensions in eastern Europe and the stirrings of a new Cold War, this former radar bunker at Ash near Sandwich in Kent has been carving out a new role as a datacenter.
Now owned by security firm The Bunker, which describes the site as the UK's most secure datacenter, the former RAF Sandwich R3 GCI ROTOR radar station was developed in the immediate post-war era as part of the extensive ROTOR air-defence network to protect the country against Soviet bomber attacks.
The R3 designation denoted an underground structure.
Behind the barbed wire perimeter fences, guard dogs patrol what was until 1998 still British defence ministry property.
The GCI in the facility's original name stands for Ground Control Intercept and reveals Ash's World War 2 origins. It was established in 1942 as part of a network of radar stations to help fighters intercept enemy aircraft once they had passed outward-looking coastal defences.
A more recent user of the site is disaster-recovery, online backup and IaaS firm Databarracks, which started hosting at the Ash bunker site 12 years ago and is one of dozens of companies to use its datacenter facilities.
Most datacenter entrances are highly secure but few feature bullet-proof glass and a guardroom permanently staffed by ex-military and police personnel.
The bunker has had a chequered history of military use from the late 1950s until it was revamped at some expense in the early 1980s, when two new bunkers were added to the original ROTOR facility.
The datacenter itself is shielded by 3m-thick reinforced concrete walls, together with gas-tight and blast-proof doors, some of which weigh several tons, and hermetically-sealed airlocks.
Databarracks has reserved space spread across several floors of the bunker, where it protects over two petabytes of data for 60 customers.
"We don't share space with other parties. We deal with regulated companies and we also do backups for central government, which requires us to do look after data to certain prescriptions," Databarracks managing director Peter Groucutt said.
"We knew what we wanted had to be a location of last resort for people's data and information. This place is run with some of the most amazing security. They do so many drills, and patrols and exercises. It really is an incredible facility. When you take a customer down there, they're very reassured."
The Ash military facility was designed to be shielded from electronic warfare countermeasures. As a result the server rooms in the bunker are each protected by Faraday cages.
The metal cages physically and electronically isolate individual areas of the bunker, providing protection against electronic eavesdropping.
Again, betraying the site's military origins, the doors that separate the bunker's rooms create hermetically-sealed airlocks. When one door is opened, the next is automatically locked until the first is closed.
Some 30m below the surface, the bunker's server rooms offer customers shared or dedicated space, ranging from a quarter rack to a dedicated suite or vault.
Underfloor cabling is a common sight in datacenters around the world but it's not conventionally hidden beneath reinforced concrete floors or accessed by trapdoors and stepladders.
All the cooling and power facilities are provided by the bunker's owners. Customers take an empty room with the uninterruptible power supplies, air-conditioning and core networking available on tap.
There is a choice of fibre, internet and telecoms providers, together with a private MPLS network.
As well as redundant uninterruptible power supplies, the Ash facility has dual high-voltage electricity sources from physically diverse paths and dual 1,700kVA auto generator backup sets.
This photo shows how, in addition to underfloor systems, cabling runs in ducting below the bunker's reinforced concrete ceilings.
Back above ground, the site's diesel generators stand ready to provide electricity in case of a loss of power.