A Special Turret, it initially has a lightning shot, but can be upgraded.

The Upgrades
Path 1: Sunderland Doubleshock ($500 in game cash) Doubles the lightning shots for serious crowd control,
Zero-K Cryo Rocket System ($800) Fires a cryogenic compound rocket to temporarily freeze zombies in their tracks,
H50 Acid Cannon ($1200) Fires a rocket detonating in a splash of concentrated hydrofluoric acid,
Ronson MK6 Flame Turret ($3250) Two big nasty tubes unleashing fiery death it touches,
"Liquid Clean" Tungsten Cannon ($25000, Must unlock first for 400 SAS dollars.) A spray of white-hot liquid tungsten. Create your very own river of pain.
Path 2: Accoustic Imaging ($200 in game cash) Echolocation Module Increases Effective Range
Passive Infrared ($300)  Additional Motion Sensors Futher Increase Range
Overdrive ($750) Upgrade Fire Control System Boosts Fire Rate
Self Repair ($1500)