Each appears in the form of an item that, when picked up, provides the player with an additional weapon with which to attack opponents, as well as some ammo for the corresponding weapon. Normally, weapons are either placed in levels by the designers or dropped by dying opponents (such as zombies in the Doom games). Once a weapon is picked up during a game, any additional weapons of the same type will count only as ammunition.
Each weapon has advantages and disadvantages when used against a given monster. Broadly speaking, however, the larger weapons do more damage but are harder to find and harder to keep stocked with ammunition. In each game, one or two weak weapons require no ammo and are therefore always available.
In multiplayer co-op (In Doom I and Doom II) Since the game doesnt restart the level when any player dies and players can easily respawn, any weapons that were placed in the level won't dissappear after its been picked up. This allow this to be an infinite source for that kind of weapon. However this does not make it an infinite source for ammo. Because of this all available players can repeatedly pick the weapon up either during the first time in level in the current playthrough or to regain it after the player had respawned after their character died. Any weapons dropped by enemies will dissappear when pick up.
No matter which weapon a player is wielding, his sprite (in multiplayer games, or source ports with a "chasecam" mode) is perpetually shown to be armed with the same generic assault rifle as the former humans; a weapon similar to this, although presumably intended to be the chaingun, appears on the game's title screen.
Early alpha releases of Doom armed the player with a semi-automatic rifle, optionally equipped with a double-bladed bayonet as a melee weapon. This weapon was not included in the finished game. The rifle sprites revealed the player character to be wearing elbow pads, which can still be seen on the player character sprite. A few other weapons were also included in the alpha versions.
- Fists: Extremely basic close-range weapon. Never runs out of ammo, but only about as powerful as a pistol shot; normally used only as a last resort or with a berserk powerup.
- Chainsaw: Does damage like the normal fist, but four times faster.
- Pistol: The default long-range weapon. Almost entirely useless against anything stronger than a zombieman or shotgun guy.
- Shotgun: A good general-purpose weapon capable of dealing medium-high damage, especially at close range. Also works better at longer ranges than the super shotgun.
- Chaingun: Very good against large crowds of small monsters or single large monsters, but its rapid rate of fire can quickly deplete its ammo supply.
- Rocket launcher: Fires explosive rockets. Does a lot of damage, but can also seriously hurt the player if used indiscriminately at close range.
- Plasma gun: Shoots pulses of blue-hot plasma at high speed, which can take down groups of incoming enemies easily — if aimed properly.
- BFG9000: The "Big Fu**ing Gun." Somewhat counter-intuitive to operate at first, but kills almost any monster in one shot.
The chaingun and pistol both use the same ammo type (bullets), so using either will also affect the other in ammo. The shotgun and super shotgun (see below) also share their ammo pool (shells) as do the plasma gun and BFG9000, which both use cells.
All of the above weapons, with the addition of:
- Super shotgun: A double-barrelled, sawed-off shotgun which takes even longer to reload, but at close range is even more deadly than the regular shotgun.
All of the above weapons, with the addition of:
- Unmaker: A demonic laser gun which rapidly fires paralyzing red slugs but can be upgraded in firepower by the collection of Demon Keys. The red slugs stun monsters, temporarily rendering them unable to attack for about 2-3 seconds. Monsters are still able to move, however.
All of Doom's weapons are present in some form in Doom 3, with the addition of:
- Flashlight: Not a weapon per se, but it doubles as a crude club.
- Machine gun: Similar to the chaingun, but not as powerful (more accurate though).
- Grenades: Standard thrown fragmentation grenade on a timer.
- Soul cube: Charged by killing monsters, and then released as a powerful seeking weapon that transfers health from the monster it hits to the player.
The Doom 3: Resurrection of Evil expansion pack contains all of Doom 3's weapons except the Soul Cube and the Chainsaw, but introduces a version of the gravity gun called the Grabber, and includes the super shotgun (as in Doom II). It also introduces an artifact somewhat like the Soul Cube.
- Burst Rifle - Repeating rifle that fires three-round bursts. Multiplayer only.
- Frag Grenade - Hand held explosive weapon.
- Gauss Cannon - A weapon that fires a huge burst of energy forming a one shot kill.
- Heavy Assault Rifle: A machine gun like rifle that can have a missile pod attached to it.
- Hellshot - A semi-automatic hell-energy weapon. Secondary fire can cause flame damage over time. Multiplayer only.
- Hologram - A image projector of a still of the Doom Marine used to distract enemies.
- Kinetic Mine - A Multiplayer-only mine that when set up leaps at its victim when close enough.
- Lightning Gun - Short range energy weapon that fires a constant stream of electricity. Multiplayer only.
- Mark V Pistol - A Multiplayer-only chargeable pistol.
- Personal Teleporter - Multiplayer-only device used to teleport the player to where it is deployed.
- Reaper - Multiplayer-only weapon that unleashes six round bursts of energy
- Shield Wall - A device that, when activated, creates a shield that neither enemies or projectiles can pass through.
- Siphon Grenade - The Siphon field created on impact leeches health from the enemies and returns it to the thrower.
- Static Cannon - Multiplayer-only weapon that charges up to deal more damage as the player moves around.
- Tesla Rocket - A device that uses electricity bolts to attack every enemy on its thrown path, slowing down as it passes.
- Threat Sensor - A device that, when thrown, attaches to a surface and highlights enemies within its radius.
- Vortex Rifle - Multiplayer-only sniper rifle.
The majority of the weapons from Doom (2016) return, along with some new additions:
- Chainsaw - Retains the ammo-restoring capabilities of Doom (2016), but it now restores one tick of fuel over time.
- Combat Shotgun - A general purpose weapon which deals decent damage but has a short range. Returns from Doom (2016), and now takes the place of the player's starting weapon.
- Heavy Cannon - A fully automatic bullet hose which can fire either a high-damage precision shot or a barrage of micro missiles. Functionally, the Heavy Cannon is near-identical to the Heavy Assault Rifle from Doom (2016).
- Plasma Rifle - A fast-firing energy weapon with the ability to overload enemy shields. Returns from Doom (2016), albeit with a redesign resembling the classic look.
- Rocket Launcher - Fires poweful rockets which can either lock onto enemies or be remotely detonated. Returns from Doom (2016) with a visual redesign.
- Super Shotgun - The Doom Slayer's personal Super Shotgun. It now features a meat hook, which allows the player to pull themselves towards enemies.
- Ballista - A slow-firing but heavy-hitting energy weapon which uses the same ammunition as the Plasma Rifle. Replaces the Gauss Cannon from the previous game.
- Chaingun - A fast-firing bullet hose which shares its ammunition with the Heavy Cannon. Returns from Doom (2016).
- BFG 9000 - An extremely powerful weapon which fires a ball of green energy. Tendrils will snake out from the projectile towards nearby demons, dealing massive amounts of damage. Returns from Doom (2016).
- Unmaykr - A reimagining of the Unmaker from Doom 64, now with a Maykr aesthetic. Uses the same ammo pool as the BFG and can only be unlocked after completing all six Slayer Gates.
- Crucible - A new melee weapon which can kill any non-boss demon in a single hit. The Crucible requires ammo pickups which, like BFG ammunition, can only be found in certain areas of the map.
The Doom Slayer additionally comes equipped with the Doomblade - a wrist-mounted retractable blade which is used in many glory kills - and the Equipment Launcher . The Equipment Launcher is used to activate the Slayer's flame belch and fire either fragmentation or ice grenades at enemies.
Heretic's weapons are more or less equivalents of Doom's weapons, except for the Firemace. Also, each weapon that uses ammunition has its own kind rather than sharing ammo like some Doom weapons. The Doom equivalent of each Heretic weapon is listed in parentheses below:
- Staff (Fists)
- Gauntlets of the Necromancer (Chainsaw)
- Elven Wand (Pistol)
- Ethereal Crossbow (Shotgun)
- Dragon Claw (Chaingun)
- Hellstaff (Plasma gun)
- Phoenix Rod (Rocket launcher)
- Punch Dagger
- Assault Gun
- Mini-Missile Launcher
- Grenade Launcher
- The Sigil of the One God