[jester]

When I said "gun turrets" I was thinking along the lines of the 5 inch gun mounts or the modern 120mm mounts that are used today or at least until recently. Like the guns on a destroyer. Those could be removed as a unit and mounted in a fort or on a railcar. As for the LARGER guns one would find on a cruiser or battleship, strip one or two out of the turret <which go down several decks, really those are more for the magazines and machinery for moving the entire turret>

Imagine if you will, a tall mountain <think Guns of Navarone> with such a monster gun. And it is the only passable area the gun covers, to bipass would mean you would have to go around and through mountains or worse, contaminated areas. It is more of a control and denial weapon. This can be the same for a straight, or channel or canal or channel. Again denying the enemy or whomever you dislike from using the area for fear of the weapon along. A psychological weapon for sure. Or, the weapon is mounted to a hull, and floated as a firing platform to an area to cause havoc to an enemy area. Take a naval gun say a 16 inch gun, put it on a railcar, then mount the rail car with a section of rail on the topdeck thus, allowing you some deflection to make adjustements. The ship points the gun in the general direction. The gun crew make smaller adjustments and then fires. The gun rolls down X distance of track and the gun is repositiononed to be fired again.

I can see several scenarios where the LARGE naval guns could be your reason for a PC campaign.