The National Security Agency is building one of the largest and most expensive data centres as a place to gather and analyse intelligence data.

At $1.2 billion, this is the largest Department of Defense construction project underway. Officals broke ground at the site 25 miles south of Salt Lake City, which will give NSA diversity with a separate data centre beyond the one it has in Maryland, says NSA Deputy Director J. Chris Inglis.

"In an era when our nation and its allies are increasingly dependent on the integrity of information and systems supported, transmitted or stored in cyberspace, it is essential that that space is as resilient and secure as possible," says Inglis in a written statement.

NSA is the lead agency at the data centre. The facility will assist various agencies, but it will be used by Department of Homeland Security and others to help protect national security networks, he says.

The government RFP for the project describes it as a Tier III, 65MWatt technical data centre occupying 100,000 square feet and described as mission-critical. It will have its own fuel and water storage, chiller plant and fire suppressant system.

The 240-acre site will be self sustaining, with its own water and wastewater treatment plants, power, gas supply, battery backup, visitor-control facilities, vehicle inspection station and perimeter security.

Construction starts this summer and will last nearly three years, partly because the government plans to spread funding for it over that period. Construction jobs could number up to 10,000 and permanent jobs once it is completed could number 200.