The rocket launcher of Doom 3 is a weapon that is first found halfway through the single-player campaign, atop a shelf in the Recycling Sector. Ammunition is generally scarce until the player reaches Delta Labs, and is known to be particularly abundant in Hell.
Unlike the Classic Doom rocket launcher, which allowed for endless firing, the new rocket launcher loads from a 5-rocket magazine. Its time interval between firing has also been increased, which limits its ability to bombard opponents. Ammunition for the Rocket Launcher is in the form of 5 or 10 shot magazines. The rocket launcher also does not have an electronic screen to serve as the ammo counter, unlike many of the other weapons which have been modified to include the aforementioned, however the player can still calculate remaining ammo by looking at how many rockets are in the clip.
Like the earlier version, it carries highly-explosive rockets and reloads fairly quickly. The rockets travel only slightly faster then the plasma gun shots, but their effects are much more devastating; a single rocket can kill, even gib, a half dozen zombies grouped together.
As in Classic Doom, short range combat is dangerous if not suicidal, especially near ledges, since the blowback effect of the rockets are much stronger than before. Medium range combat is most effective with the weapon, with the physics engine sending enemies flying, often in several pieces. The slow speed of the rockets makes long range combat difficult, unless it is being used against a large, slow-moving target. Like rockets from the demons, your own rockets can be intercepted with weapons fire, though this rarely happens outside of random coincidence.
In single player, the weapon is most effective against Hell Knights, though it can also be used in enclosed spaces successfully against Cacodemons, Revenants, and Commandos, although tentacle Commandos tend to dodge it, as can Chaingun Commandos if they are not firing. Perhaps the most effective use for the weapon is to kill Sabaoth; as the door opens, empty a clip of rockets into him. After reloading, simply use a fully charged Soul Cube, and you will send him back to Hell in under 20 seconds.
While it provides only minimal blowback in single player for rocket jumps, in multiplayer it makes a useful, albeit health-draining, height booster for your jumps.
- It's very strange that Rocket Launcher ammo capacity keeps 1 in the last resort situation that looks like the player needs a last decision to use it or change to other less powerful weapons.
- Mysteriously, rocket projectiles can distort enemies' fires from Mancubus or Sabaoth. Sometimes it can even be used to directly stop projectiles if you have run out of plasma cells or you really assure your accuracy. Remember not to stop from Revenant, Hell Knight, or even Cyberdemon since they're faster than your feeling so conserving ammunition for use against them is a wise choice.
- Try not to fire though gaps like with bullet-based weapons (Pistol, Chaingun) or the Plasma gun, since the rocket is a big projectile and could potentially hit the gap instead of travelling straight through.
- Unlike most other weapons, the rocket launcher was not meant for combat. In a PDA, it was used to destroy debris.