In 1951, the U.S.S. Catfish, a WWII-era diesel submarine, cruised into San Francisco Bay. The crew snapped a handful of pictures through the periscope, showing what the city and Alcatraz looked like from the submariners' perspective.
It's a bit eerie to see the city through the periscope's reticles, almost as if it were a target. It offers a historical perspective a largely pre-skyscraper San Francisco, but also creates the sense that the city being spied on.
You can see more photos from the Catfish at SF Gate.