WWII Antisubmarine Net (site)

Part of San Francisco's WWII-era coastal defenses, the antisubmarine net was constructed at Tiburon Naval Net Depot and by prisoners at Alcatraz. In theory, the net, which was a system of interlocking steel rings and buoys to keep the net afloat, would tangle the propellers of an enemy submarine sneaking into the San Francisco Bay.

Stretching from Sausalito to Marina Green, the net could be opened and closed as needed for friendly vessels.