As you approach the Royal Canadian Navy's secretive Trinity intelligence centre near the Halifax Harbour, at least nine surveillance cameras track your movement.
Protected behind two chain-link fences, both topped with barbed wire, the main Trinity facility is really a building within a building.
A separate interior structure, with metal-clad walls, safeguards its secrets.
To enter the ultra-secure core of Trinity, you have to cross a walkway and pass through an airlock. The inner sanctum has the feel of a safe and is lined with electromagnetic shielding to prevent snooping.
Staff in this building, the nerve centre of Trinity, normally require "Top Secret" security clearance.
There's good reason for these extraordinary measures. This facility houses some of the most sensitive military intelligence available in Canada, not just gleaned by this country but also by allies including the United States and the United Kingdom.
It was the last post of Sub-Lieutenant Jeffrey Paul Delisle before he was arrested for allegedly spying and charged Jan. 16 with passing confidential information to foreign interests.
Investigators are now sweeping parts of the Trinity complex for bugs and anything that might have helped leak state secrets to a foreign adversary.
The secrets the sailor is accused of taking from sites such as Trinity will form the heart of the case that prosecutors are building against him.
Through a series of conversations with defence sources, The Globe and Mail has pieced together an account of Trinity's operations and its vital importance to Canadian security.
"Is there a Russian sub off the coast? Where are the American subs? Where are ours? That's the kind of top secret stuff they would know," one person familiar with Trinity said.
It receives satellite pictures, video feed from unmanned drones. Its maritime-operations centre tracks every ship entering and leaving Canadian waters.
The military is loath to reveal staffing levels at Trinity lest they indicate the importance of the facility. But those familiar with the organization estimate upward of 100 people work for the unit, although staff are dispersed among several buildings.
Trinity's job is to help the Royal Canadian Navy make sense of the world. In military lingo it's a "data fusion centre" that assembles bits of intelligence into a bigger picture in much the same way a mosaic is put together.
By nature, fusion centres cobble together intelligence from devices that spy on sea, air, and sky. But it's the awesome surveillance capabilities of Canada's allies – including the United States, U.K., and NATO – that round out the picture immensely.
Trinity also sends and receives messages from ships and has other offices that track vessels entering and leaving Canadian waters.
Canada shares maritime defence intelligence with the U.S., U.K., Australia and New Zealand through a system known informally as "Five Eyes."
Canada would have to quickly act to assure allies that it can plug any leaks in Halifax, said former Liberal defence minister Bill Graham. "The significance of this is that Canada is a member of the Five Eyes with the United States, which gives us security that other countries don't have, and the integrity of the system is paramount," he said in an interview.
Mr. Graham, who served in the role from 2004 to 2006, explained that the time-honoured intelligence-sharing relationship among this group of five was jeopardized once before – when Canada refused to join last decade's U.S.-led invasion of Iraq.
"We definitely paid a price. We definitely were shut out for about a year," he said. He added that "Canada's place in the Five Eyes gives Canada a level of security that even countries like France or Germany don't have."
Other alliances may be at stake. The NATO block of countries is girding to respond to persistent cyber attacks from China and Russia – meaning that Canada's ability to safeguard its intelligence in Halifax and elsewhere is all the more crucial.
"This is an era when cyber warfare is becoming much more significant," Mr. Graham said. "This is a piece in a puzzle, which is not well understood, even by the professionals, and it is in constant and extraordinary evolution."
American security officials cultivate close ties with Trinity. In 2003, for example, the U.S. commander of naval intelligence and his entourage visited the site. Trinity also has a co-operation agreement with an intelligence fusion centre in Virginia that's run by the U.S. Coast Guard . It has also been widely reported that Trinity acts as an extension of a U.S. underwater surveillance system known as SOSUS, which keeps an eye out for hostile submarines.
The structure that houses Trinity's intelligence operations was purpose-built, according to a local news article announcing its official opening in 1995. At the time, monitoring of underwater listening devices moved to Halifax, replacing a shuttered U.S. facility in Argentia, Newfoundland – where, in 1988, a Canadian-Hungarian was caught on videotape in a police sting trying to pay a $40,000 bribe to a naval officer for classified documents onsubmarine-surveillance technologies.
Canadian prosecutors said those documents were "useful to a foreign power, namely the Union of Soviet Socialist Republics." A number of Russian diplomats were expelled from Ottawa in the aftermath of that 1988 arrest.
How sensitive are the data systems inside Trinity?
Likely very sensitive, according to publicly tendered contracts. They show that technicians who fix computers at Canadian Forces Base Halifax, which includes Trinity, sometimes need seemingly absurd levels of security clearance to peek inside the secure data networks. For example, "Cosmic Top Secret Clearance, Special Access Category III" is required to look at live data on some servers.