Npc turret ground
Combine ground turret
Note: In the Nexus building (the d3_c17_10b map) these were seen entrenched within the floor, and could only be killed by blast damage, like lobbing a hand grenade inside its lift. That lift, and the ability to destroy the turret, is not part of this entity. (The lift was a func_door brush rig, and the player really killed an invisible npc_bullseye, filtered to be killed by blast damage only by a filter_damage_type, that signalled the turret to descend and lock.