Google has a barge. They’re not telling anyone what it’s for. Now, there’s a new rumor floating around about what it actually is.

The U.S. Navy had its share of secrets on Treasure Island, but few were better kept than what’s taking place on a mysterious barge just off the island.

The barge, with a four-story stack of shipping containers, is out in the open for all to see. But the project’s purpose has been kept under wraps, and virtually no one wants to talk about it for the record, from the harbor office at Clipper Cove to the Treasure Island Development Authority to the U.S. Coast Guard.