The shotgun of Doom 3 is a devastating close-range weapon. It can be first found in Mars City Underground on either a shelf or in the large room with multiple generators.
The Doom 3 Shotgun is the pump-action version, and holds 8 shells at any one time. It is also the only weapon in the Doom 3 arsenal which allows for firing during reloading. Ammunition for the shotgun is in the form of small packets or large boxes of Shells, as well as deceased Shotgun Zombies. Ammo is generally easy to find throughout the entire game, and since much of the fighting takes place in tight corners, the Shotgun usually serves as the main weapon of choice until the harder levels, where it would fall as a secondary weapon. Compared to the classic Doom counterparts, this Shotgun has a wider spread making it a deadly weapon at point-blank range, but less effective at further distances. The Shotgun also has a "double" shell reload action: although the reload animation shows Doomguy loading only one shell at a time, the loaded ammunition counter increases by two - this is perhaps to save time and provide a faster reaction to the player so they won't be vulnerable to enemy attack during a delayed reload process.
Due to its wide spread, it is almost useless at long range, making it only useful for close encounters. It's twice as powerful as the original shotgun (in effect doubling its function as a replacement for the classic double-barrelled shotgun). Unlike the super shotgun of Doom 3, this is a pump-action single-barreled shotgun and isn't the same kind as the classic shotgun (which is a Mossberg 550 model).
The Shotgun works best against Imps, Zombies, Demons, and Cacodemons, since they try to rush the player, giving the shotgun's high short range damage an advantage. In contrast, enemies with higher health and/or at longer distances will not be good targets. For example, fighting Z-Secs with the shotgun is generally not a good idea, due to their faster rate of fire and their tendency to maintain distance from the player. To maximize ammo efficiency, remember to get very close to your target before firing so that as many pellets as possible make contact with the target. If an enemy has a melee attack, trick it into using the melee attack, then shoot. This works best for Tentacle Commandos.
The Shotgun is useful until the start of Delta Labs, where powerful enemies such as Commandos and Arch-Viles start to appear. It is strongly recommended to avoid using it against stronger enemies, as the necessity to approach at close range will put the player at a grave risk of taking heavy damage from these enemies' counterattacks. However, once you soften them enough from a distance, you can get up close and unleash the Shotgun to finally take them down.
For weaker enemies that usually die from one shotgun shell, if most of the pellets make contact but the target is still alive, the player can quickly draw either the Pistol or Machine Gun and finish it off to maximize ammo utilization.
Due to the view model being shown as diagonally turned left in the player's hands, the shotgun in Doom 3 does not feature any open sights like the original shotgun (which was centered in the forward position), so it does offer a guide to aim accurately without the aid of the crosshair presented on the HUD.
- The Marine in Doom 3 is often seen wielding the shotgun in cutscenes of the game. He is also seen wielding it in official artworks. Due to this, as well as the fact that much of the fighting takes place in tight corridors, the Shotgun is considered to be the flagship weapon of the game.