Google image from the Associated Press.
SAN FRANCISCO (USA TODAY) - The Coast Guard on Wednesday visited the mysterious "Google barge" floating in San Francisco Bay, but the agency would not reveal anything about the tech giant's hush-hush vessel.
Google has refused to acknowledge any connection to the barge and three others like it. But it is zealously guarding its privacy around the four-story stack of containers docked at a pier on Treasure Island and a companion in Portland, Maine.
At least one Coast Guard employee has been required to sign a non-disclosure agreement with the company regarding the San Francisco project, Petty Officer 2nd Class Barry Bena told Reuters. An inspector with an unidentified California agency said he, too, had to sign such a document.
Bena told USA TODAY on Wednesday that he was later instructed by superiors to say nothing.
"Commercial confidentiality prohibits me from talking about this," said Bena, a spokesman with the Alameda district office. He added that he is not authorized to sign non-disclosure agreements.
Before the cone of silence fell on the Coast Guard's public affairs office, still another spokesman confirmed to the Portland Press Herald that Google "is involved or associated with the barge but there is a non-disclosure agreement in effect."
All the Coast Guard would say about its visit is that it was not for a fire or medical emergency, the San Jose Mercury News reported.
STORY: The mystery of Google's floating barges
The steel-hull barge belongs to By and Large LLC, of Wilmington, Del. Built in 2011 by C&C Marine in Belle Chasse, La., it is almost 250 feet long and 16 feet deep - significantly longer and deeper than a standard freight barge.
Its purpose remains shrouded in the fog of secrecy, however.
Tech site CNET has speculated that it might be a floating data center, while the local CBS TV affiliate points to a floating store for Google's wearable Glass computer.
The executive director of the Bay Conservation and Development Commission told the Mercury News that attorneys for the project said they planned on "using the vessel as a tool to teach about technology."
A Treasure Island worker offered the barest of details about what has been going on behind the shrouded scaffolding:
Bob Jessup, a construction company superintendent who works in a building across the street, said Google spent the past year working on the project. He said they fenced off a wide area and brought in at least 40 welders a day, who worked around the clock and refused to say a word.
"They wouldn't give up any of the information," Jessup said. "It was a phenomenal production. None of them would tell us anything."
He said they worked on the inside and the outside of the shipping containers, outfitting them with electronics - "very hush hush" - and then loaded them onto the barge with a crane. They put sides on the containers, with glass windows in some of them. They had to weld them very precisely so they could stack, Jessup recounted.
Coast Guard spokesman Lt. Joshua Dykman told the Mercury News that he had been ordered not to discuss the barges for "legal reasons." He said he had not signed a non-disclosure agreement.
"Once the project is completed, we will be releasing information," he said.
As for its Maine companion, work is not expected to begin until after the San Francisco job is finished, a local Coast Guard spokesman told the Portland newspaper.
Ensign Connan Ingham said that no non-disclosure agreements had been signed but that some local agency officials "have been asked by the owner not to talk about it."
"They are fully aware of what's on that barge," he said.