Over the past six years, the National Security Agency has quietly transformed the former Sony chip fabrication plant on the Northwest Side into a black-box hub of intelligence gathering and data storage.

Satellite and aerial imagery show massive air conditioning units and backup generators have been added to the facility, which now is ringed by barbed-wire fencing. City permits and property tax records show the complex has been dramatically expanded.

But details of the project have been shielded by a level of secrecy that is uncommon even for the NSA, an agency the U.S. government refused to officially acknowledge for decades, earning it the moniker “No Such Agency.”

Longtime observers of the intelligence agency say they believe the San Antonio plant has a mission similar to the agency's other new facilities in Georgia and Hawaii, where communications intercepted by NSA are translated and then sent to headquarters in Maryland for analysis.

Tax records also show it has built a roughly 94,000-square-foot data center at the site.

With the facilities in Georgia and Hawaii, as well as with other major construction projects, the NSA included the costs as line items in the Defense Department's budget. But it hasn't done so with the San Antonio location.

In a written statement, an NSA spokeswoman said funding for the project followed normal protocol. However, she didn't identify the budget item that Congress approved for the expansion.

The spokeswoman said the facility became operational late last year.

The agency has come under intense scrutiny since contract employee Edward Snowden leaked documents to the Washington Post and British newspaper the Guardian, revealing the NSA had systematically collected phone records from at least one phone company and established a program, called PRISM, that swept up vast amounts of information from Internet firms.

NSA chief Gen. Keith Alexander testified before a U.S. Senate committee Wednesday that the controversial surveillance programs are legal and have helped prevent terrorist attacks.

Missing numbers

The agency has been on a publicized building spree over the past several years. It has issued news releases touting the Hawaii and Georgia projects and announced groundbreakings on a massive data-center in Utah and a high-speed computing center at its headquarters in Fort Meade, Md.

Funding for those projects was included in the Defense Department's unclassified budget, making the location and amount spent part of the public record.

However, a San Antonio Express-News examination of funding for major construction projects listed in the Defense Department's budgets from fiscal years 2004 through 2013 found no appropriations for the extensive work at the old Sony plant.

“I would have thought that funding for the San Antonio facility would be handled about the same as that for Utah or Georgia, and I can't immediately think of why it wasn't,” said Steven Aftergood, director of the Federation of American Scientists' government secrecy project.

He added that because satellite imagery from around the world is readily available these days, intelligence agencies attempting to obscure major construction projects in their budget seemed “quaint.”

Matthew Aid, a historian and NSA expert, also reviewed the Defense Department's budgets since January 2001 and found no classified or unclassified expenditures that would explain how the NSA financed the project.

“I went state-by-state,” said Aid, author of “The Secret Sentry,” a history of the agency. “I went through all projects for Texas, and then I went through all minor construction projects. I went through family housing, looking for any corollary projects or looking for ways they were possibly trying to hide this stuff. And I found zippo.”

He also said it appeared that someone had taken care to minimize the profile of the NSA's operation at the former chip plant, noting that government and military websites returned a total of seven web pages that contained the phrase “Texas Cryptologic Center,” the official name for the agency's operation in Texas.

The Express-News also discovered a Defense Department Inspector General report on the construction of the facility, which was marked unclassified on the IG's website Tuesday. However, when the newspaper requested a copy of the report, a spokeswoman for the IG said it had been mislabeled and was “For Official Use Only.”

Corporate Office Properties Trust, a publicly traded company based in Maryland, owns the San Antonio facility. COPT leases it to the NSA.

Property tax records show it has grown by nearly 135,000 square feet, from nearly 498,000 square feet to almost 633,000. In 2008, the facility was worth $33.5 million; now, it's valued at more than $72 million.

Aid said he believed the function of the NSA's San Antonio building would be largely similar to the agency's operations in Georgia and Hawaii, which the agency has said cost $286 million and $358 million, respectively.

In a 2006 document related to a municipal bond sale, City Hall estimated the NSA's new investment in San Antonio could reach $300 million and add up to 1,500 new jobs.

The securities filing didn't identify the site of the new investment, but the first applications for permits to begin work at the Sony plant were filed in May 2006, said Ximena Copa-Wiggins, a spokeswoman for the city's Department of Development Services.

Searching for project funding that an intelligence agency is trying to keep secret is nearly impossible, Aftergood said.

“It's the equivalent of astronomers searching for dark matter,” he said. “You look for the parts of the budget that aren't accounted for, and up to a point, you can suss out some billions of dollars that aren't accounted for.”

Another defense budget expert, Todd Harrison, a senior fellow with the Center for Strategic and Budgetary Assessments, agreed, offering an example: If the NSA had structured the lease in such a way that the property owner actually paid for the improvements, which the NSA then covered with a higher lease payment, the project likely would be hidden in the department's operating budget.

According to COPT's 2012 annual report, the former Sony plant was being leased for $34.69 per square foot at year's end — significantly more than the citywide average of $21.52 for office space during the last three months of 2011.

Secret histories

The NSA long has had a significant presence in San Antonio at Joint Base San Antonio-Lackland's Medina Annex, where — as of 2005 — 2,000 military personnel and civilians translated communications intercepted by the agency. Lackland also was named home of the 24th Air Force, also known as the service's cyber command, in 2009.

In 2007, Mario Hernandez, president of the San Antonio Economic Development Foundation, said the NSA was looking to move its staff from the Lackland offices to the Northwest Side location, where it also planned to build a data center. The agency confirmed Friday that the move had taken place.

When the NSA announced it had selected the Sony site in 2005, the agency initially was fairly open about the project, even holding a public job fair at a hotel to recruit potential employees.

That all seemed to change after funding for the project was put in limbo for months, beginning in 2006. When the project got the green light again in April 2007, it was then-Congressman Charlie Gonzalez, D-San Antonio, who announced the news.

Ever since, the NSA has maintained near-radio silence about the project. One incident, however, prompted the agency to break it.

In 2010, residents who lived near the facility complained that their garage doors were randomly opening. The NSA issued a statement acknowledging an antenna it was using interfered with garage door openers.

What the NSA would be doing at the site wasn't really a concern as officials worked to convince the NSA to expand its presence in the city, said Gonzalez, who now is in charge of VIA Metropolitan Transit's marketing, government affairs, media relations and government outreach.

“All we ever looked at (was) 'how many quality jobs will it create?'” he said.