There are six different types of turret available to build in the game. They are split into two sizes; small and large. A small turret can be built on any open space, while large turrets can only be built on large spaces.
Turrets can be upgraded a total of two times. Turrets also take damage, and if they are damaged too severely they can be destroyed.
Turrets can either operate on their own, or you can take direct control of them to aim and use the special fire modes (like Machine Gun III's grenade launcher or Anti-Tank III's Shell Cam mode. You can only only earn Barrages when you are directly controlling a turret.