I always wondered what that was!

[Zee]

Back when I used to fish the bay regularly I always wondered what the heck that bugger was. Turns out the top part of the crane was used to launch missiles back in the day. Trip!

Lots of really cool pics and info on that area (military ruins) and the bay's past here:
http://www.flickr.com/photos/telstar/sets/56935/

Z

[Mooch]

something interesting on the same subject....

http://oaklandmofo.com/blog/star-wars-at-at-walkers-port-of-oakland-cranes/

[promethean_spark]

They didn't launch missiles off it, it was a test stand that held rockets in place to measure their performance.  It's still done nowadays, but generally in less populated areas.  It needs to be high up so the rocket plume doesn't dig a huge hole in the ground.

[Zee]

They didn't launch missiles off it, it was a test stand that held rockets in place to measure their performance.

I think we're both right on this one.

""OPERATION SKYCATCH--This sequence shows how a huge overhead assembly at the San Francisco Naval Shipyard catches a multi-ton dummy Polaris missile in mid-air and keeps it from free-flight. Left to right: Powerful blast sends missile skyward. At top of its trajectory, it is snubbed by modified arresting gear engine. Then the dummy Polaris is lowered for examination removal of instrumentation, and preparation for next test. In earlier testings the missile was hurled out into San Francisco bay and then retrieved. Lockheed Missiles and Space Division, who released these pictures, said this new method permits accurate study on dummy missiles which are structurally identical in live Polaris missiles."
Image here: http://www.flickr.com/photos/telstar/18359898/in/set-56935/"

[Jeffrm20]

Mythbusters have done a few experiments at that site, the Archimedes Death Ray and the 360 degree rocket swing.

[piski]

Wow cool, I never know'd it! Thanks for sharing - I've been curious about that stuff, too.