Z-Sec

The Z-Sec (Zombie-Security) is the second class of Zombies in Doom 3 the player will encounter. Unlike the basic Zombies, the Z-Secs are a closer recreation of the classic former humans, utilizing firearms to attack the player.

Z-Secs were originally Mars-Sec personnel (UAC security guards) who were possessed by the demonic spirits of Hell, turning them into hostile undead soldiers.

By the time the invasion begins, the player will see a brief footage through a monitor, of a guard being possessed by a ghostly skull, causing his skin to turn pale and his eyeballs to explode. Shortly after slaying the zombified Ishii, the player will witness a Marine having his neck snapped by a Pistol Guard Z-Sec through a communication terminal, shortly before another Z-Sec appears to attack him.

Combat characteristics
Z-Secs are known for their artificial intelligence, allowing them to behave and fight competently like enemy soldiers. They can rely on tactics such as maintaining their position, taking cover, or crouching to present themselves as less available targets. Z-Secs also do not suffer from slow movement like the regular Zombies, as they possess the same speed and agility as a normal human soldier, although they are not as mobile as the player.

Z-Secs mostly patrol around solo, although they can occasionally come in small squads of two to four. Z-Secs also appear to use radio chatter, although this is used more as an auditory cue to warn the player of their presence, rather than them relying on group tactics or teamwork through radio communications to take down the player.

There are four types of Z-Secs, each with its own distinct characteristics and firearms. These are the Pistol Guard, Shotgunner, Machine Gunner, and the Riot Shield Trooper.


 * Pistol Guard: Similar to the classic Zombieman. It is a bald man with no helmet and glowing white eyes, armed with a pistol. They have the unique ability to dodge by rolling sideways, and always retaliate with a few pistol shots after a successful dodge. They occasionally fire multiple shots in rapid succession before pausing to take cover, but they are most likely to miss compared to the other Z-Secs. They have about half as much health as the other Z-sec types. Drops a Pistol when killed.


 * Shotgunner: Similar to the classic Shotgun Guy, but wears a helmet with a broken visor, and completely hollowed eye sockets, armed with a shotgun. If it spots the player from a distance, it will rapid-fire multiple shotgun blasts before momentarily pausing to take cover. This Z-Sec, however, will occasionally rush towards the player to fire at point blank range. Drops a Shotgun when killed.


 * Machine Gunner: A rough equivalent to the classic Heavy Weapon Dude, it wears a fully intact helmet with a blood-spattered visor (obscuring its eyes) and a breather, and relies on the machine gun. They will often maintain their position from a distance upon spotting the player, firing multiple bursts before momentarily pausing to take cover. If the player closes in, it will generally approach the player's position. This Z-Sec type is the only one that can fire and run straight at the player at the same time. Drops a Machine Gun when killed.


 * Riot Shield Trooper: The rarest Z-Sec type, appearing only in one level (Central Communications Tower). Has the same appearance as the Machine Gunner. In addition to the Pistol, this type carries a large riot shield, which is impervious to any firearm projectiles. This Z-Sec will also occasionally kneel down while holding it's shield to make itself less available as an easy target. Drops a Pistol when killed.

Tactical analysis
Z-Secs are comparatively more dangerous than the classic former humans as they are much more intelligent and proficient with their weapons, firing more frequently with better accuracy.

Fortunately being former humans, they are still defensively weaker than the most basic demon like the Imp, and they are much more vulnerable to headshots. Using cover is extremely important when fighting these enemies, as their hitscan weapons cannot be dodged as easily as most plasma based projectiles fired by most demons.


 * Pistol Guard: The Pistol works well against this type, as it take four bullets to the body to kill it. It is often a good idea to keep a good distance as it is more likely to miss its mark when the player is far away. Other weapons like the Shotgun and Machine Gun are also effective are taking them down from close range or long range, respectively.


 * Shotgunner: This type should be brought down as quickly as possible, as it is capable of dealing a great deal of damage if left unchecked. Using the machine gun to soften it up at range and then finishing it off when it gets in close is an effective strategy, but caution should be taken to only come out of hiding after it has fired a shot. More powerful weapons should be considered. Running straight at it is definitely not recommended, as you risk yourself from its point blank shots from its weapons. Alternatively, you can hide behind a doorway and wait for it to charge then blast it with the Shotgun. This works most of the time, but be prepared to fire again if they survived the first shot.


 * Machine Gunner: Although it fires more than the other types, its bullets are less powerful. Patience is a good tactic, as it tends to pin down the player with prolonged sprays. It is effective to wait for it to come out of hiding, shoot and quickly duck down behind cover before it opens up. It is a bad idea to fire prolonged bursts at it, as it is tough enough to recover swiftly from hits, often enabling it to retaliate swiftly. Machine Gunners do not fire and move at the same time, and so they are vulnerable to return fire when advancing forward towards the player's position. Alternatively, you can use the same doorway tactic as with the Shotgun Guy. This tactic works better against Machine Gunners because even if it survives the first shot, it will take the time to crouch before shooting you, allowing you to get in a finishing shot.


 * Riot Shield Trooper: While this guy's riot shield makes it impervious from any attacks, its shield does not fully protect its entire body, even when it kneels. The best target is to go after its exposed body parts, such as its legs, or its head where the shield does not protect it. The Machine Gun can make this a very helpful strategy to take it out from afar. Alternatively if you want to take it out through close range, the best way is to run into it with the Chainsaw, as it will damage it even when the shield is hit. This strategy works better if you can hide behind doorways to lure it into your corner and unleash your Chainsaw. Another possibility is to hit it with a grenade or with a rocket.

Trivia

 * When you pick up the PDA of Seamus Blake in Communications, one of his E-mails is a receipt for a CD of music called "Champagne Tomiko" by "The ZSecs".
 * The Riot Shield Trooper's Pistol uses the same gunshot audio as the player's Pistol. Curiously, this doesn't apply to the Pistol-wielding Z-Sec's weapon, despite being the same thing.