Turret Hardpoint
From Official Barotrauma Wiki
Empty hardpoint where a turret can later be mounted.
If placed in the editor and linked with a Periscope Base and Loader Base it can be upgraded at an outpost to have turret. Which will convert the hardpoint and loader to the selected gun, and the periscope base becomes a regular periscope.
It has the same wiring configuration as a normal turret.
Used for making custom submarines that start with optional hardpoints.