Was the bridge brought down to prevent something from leaving or getting into the bay?

That’s interesting. The bay remains open, but. All traffic in and out of the harbor will be diverted. So traffic in the bay is going to decrease.

What if.
Limiting the surface traffic also limits the underwater traffic? As in, it would make it harder for submersibles to hide in the shipping lanes if there are no ships in them. It would also have a reverse Pearl Harbor effect, in that it closes off the harbor to an attack from the water.

The onion has so many layers.