What is this airplane doing?

Factual Questions
1

Almost every weekday I see a fighter jet (it looks like a black or other dark-colored F-5 pass over the Golden Gate Bridge from west to east flying towards the North Bay & Delta, near where the Concord Naval Weapons Station is. It always passes over at about the same time too, somewhere between 1 and 3 pm. I can’t figure out why this happens every day (seemingly). I was thinking that if they were holding some sort of exercise, I’d see it for a few days, and then it would stop.

Any ideas?

2

Might be some T-38’s (they look much like the F-5) with new pilots getting some kind of practice in…

3

The Golden Gate bridge is also considered a high risk target for terroists too. Might just be someone keeping an eye on things from above.