Captial ship's turrets are dirty cheaters
I was doing some Practice Mode on a stardestroyer, and as an experiment, I decided to destroy every gun and missile turret on it, rather than trying to finish it off. I wanted to see if it was possible to make it completely stop shooting.
It turns out, you can't. I found two interesting things about the gun turrets on a stardestroyer.
First, I think that some of the turrets from the other side of the superstructure can turn around and shoot you through the superstructure. Not 100 percent certain of this, because the second thing makes it hard to test.
Second, and this one I'm sure about, is that there are "invisible" turrets which shoot lasers at you, from several different places on the hull, which cannot be destroyed and which are not visible as objects on the hull which you can locate and shoot. You can shoot every turret on the surface of the stardestroyer and it will still hit you with blaster fire.
You can get it to stop launching rockets by taking out the rocket turrets, but it will still always hit you with some amount of laser fire.
I imagine some stormtroopers opening a window and shooting at you with their blaster rifles.