The idea of the turret enemy is that it will stay in one place and shoot at you. They usually spawn on high ground, where Archers would stand. Here are the different Marks.
Mark 1 Turret - Two bows that shoot at the player.
Mark 2 Turret - Shotgun with long reload but large spread.
Mark 3 Turret - Machine gun with high accuracy. Fires in quick rounds of 10.
Mark 4 Turret - Tracking missile! Will stop tracking after 5 seconds.