Chaingun/Doom 3

"The Chain Gun's 0.30 caliber armor piercing round delivers substantial damage, but heavy recoil reduces accuracy."

- PDA Description

The Chain Gun (also known as the UAC Weapons Division Mach 2 Chain Gun) in Doom 3 is a good mid range weapon with a high rate of fire. Unlike the classic chaingun, the Doom 3 Chain Gun has an ammo counter and is considerably more powerful. While the old chaingun was, at best, a light rapid fire weapon that was clearly inferior to the plasma rifle and, at best, compared to the machine gun, Doom 3's Chain Gun is more on par with the plasma gun.

Weapon Schematics
The Doom 3 Chain Gun differs from its original; there is a slight wind-up time (around 1 second) for the barrel array before it begins firing. Also, unlike the classic chaingun, which fired the same standard rounds as the pistol, the Doom 3 Chain Gun now utilizes exclusive .30 caliber, armor penetrating rounds, easily outclassing the Pistol and Machine gun in terms of firepower. Ammo for the Chain Gun can be found in the form of Ammo Belts (60 rounds) which appear as ammo cans about the size of a briefcase, and can also be obtained by picking up Chain Guns (30 rounds) from deceased Chaingun Commandos. Just like the plasma gun, BFG9000 and newcomer Machine Gun, the ammo counter is located on the weapon itself, instead of the game HUD.

Tactical use
The Chain Gun is the gun-of-all-seasons, to say the very least. High accuracy and rate of fire make it a good weapon to use anywhere from close to far range situations against almost any low to mid-range foe. Even a Hell Knight can be taken down with less than 5 seconds of concentrated fire.

Although it has stupendous firepower at any length, both short and long range use is discouraged. Short range attacks mean possibly being taken down by a melee attacker (such as a tentacle Commando zombie) in a situation where you want a sudden burst of heavy damage to lay down a lot of pain within a split second (say, with a shotgun).

Due to its noticeable bullet spread, long range combat is also discouraged. Additionally, the Chain Gun has no splash effect damage, meaning that unless the target stands perfectly still or you just fire blindly in the target's movement range (which means wasting ammo), a lot of the shots will miss the target and result in wasted ammo.

The best situation is a relatively slow, large monster that affords enough time to be taken down and requires a steady stream of fire to be taken down, and is big enough that it will still catch all the shots despite the Chain Gun's inaccuracy. Pinkys and Cacodemons come to mind, as does the Vagary. Also, a group of Trites or Lost Souls can easily be taken down with some blind firing.

As Chain Gun ammunition is generally hard to find until the player reaches the Delta Labs (and even then is mostly retrieved from the corpses of Chaingun Commandos), it is recommended to use the Plasma Gun first for all levels leading up to the aforementioned level.

It is possible to "pre-spin" the Chain Gun, and keep it revved, allowing it to be used in tight quarters effectively. This also makes the Chain Gun more effective at these ranges by being able to conserve ammo and also more devastating than the shotgun for quicker takedowns of enemies that require more than one shotgun blast to kill.