"Fate has chosen us to take a stand. Mount a defense." ― Oksana
Defense systems are an integral part of any stronghold in World War Z.
When a swarm is imminent, your team will need to rely on strategically-placed defense systems to aid you for the battle that is sure to come.
The Exterminator Class
The Exterminator possesses a one-of-a-kind perk unique only to them with a power that cannot be understated. This perk is called. This perk gives the Exterminator a chance to duplicate defense systems after putting one down. Being able to put down more defense systems in an area where a large swarm is expected is incredibly alluring because the addition of an extra one or possibly more can easily sway the battle more in your team's favor.
If there is an Exterminator on your team that is at least level 16 and does not use Claymore Mines as his equipment, it is safe to assume they have the Combat Engineer perk activated. As a teammate, be aware of such Exterminators in your team and always give them full priority of collecting defense kits. As an Exterminator, be sure to communicate with everyone else that you can create more defense systems and that it would be appreciated if they refrain from taking any kits and instead mark any that they find for you to collect.
The Automatic Turret is a remote machine gun defense system. When placed, the Autoturret will scan a large area in front of it for zekes. The bullets fired by the Autoturret cannot harm survivors even if they stand directly in its path. After firing for some time, the Autoturret will eventually run out of bullets, indicated by a yellow flashing light and the barrel of the gun pointing down. It will need to be manually restocked before it can fire again.
An enemy variant of the Autoturret exists. Distinguishable by their red tracking laser, they will target both zekes and survivors, whichever is standing closer in front of it. They can be captured to only shoot zekes or be destroyed. While in their hostile state, they are not required to be restocked.
The Barbed Wire is a sharp barrier defense system. When placed, zekes that run up to it will be forced to climb over it. There is a very high probability of a zeke getting caught within the sharp steel fencing and eventually dying. The more zekes caught in the Barbed Wire, the less likely that it will catch zekes in them. Some special zombies are unaffected by it and will always manage to climb over it. When broken, the Barbed Wire will be largely flattened and collapse onto the floor.
The Fence is a tall barrier defense system. When placed, zekes will be blocked from passing through and will be forced to climb over it. Small zeke pyramids will form if enough zekes congregate to it. The more zekes there are pushing up against it, the quicker it will be for them to break it. When broken, the Fence and all the zekes that were against it will crash to the floor.
High Voltage Grid
The High Voltage Grid is an electrocuting barrier defense system. When placed, zekes that come in contact within its area of effect will be stunned, staying in place and taking damage until they die. The High Voltage Grid can only be placed on certain fences that are either on the floor or standing up. After dealing enough damage, the High Voltage Grid will cease to function as indicated by a red light.
The Mortar is an explosive launching defense system. When placed, survivors can manually use it to kill zekes by placing a mortar shell into the tube to launch it in a specific spot. The shells explode on impact and cause a powerful explosion capable of killing dozens of zekes at a time.
The Stationary Machinegun is a manned machine gun defense system. When placed, survivors can manually use it to kill zekes by firing a fast barrage of explosive bullets in an area in front of them. Although the gun has a high rate of fire, there is only a slight recoil when it is fired.