Devastators are the most straightforward and iconic of the Space Marine Heavy Support choices. A squad of Marines that can take up to four heavy weapons, Devastators provide a stationary firebase. I prefer to take them as a full ten Marine squad, as the extra bodies protect the heavy weapons and the ability to Combat Squad allows them to engage two targets and cover more of the table.
The main question with Devastators is what heavy weapon to give them. I always suggest taking four of the same weapon, as this means they have the same target preferences and range. Missile launchers are a common option because they can target both infantry and vehicles fairly well. Flakk missiles are an option here; they are quite expensive but they do allow your Devastators to reliably shoot down fliers. If you don’t have any other anti-air and are taking Devastators, it’s worth spending the points for flakk. Lascannons are your best option for anti-tank, while plasma cannons will chew through heavy infantry very well. Heavy Bolters are an option, but there are generally better options for anti-light infantry fire (we’ll get to it in a bit). Multi-meltas, while great weapons, don’t do their best work on such a stationary platform due to their short range. You will be better off taking them on Attack Bikes or Speeders.
The Imperial Fists Chapter Tactics really make Devastators amazing by granting them Tank Hunter. While this potentially helps any of the Devastator builds, it is amazing on lascannon Devastators. They will destroy most enemy vehicles very quickly, and even offer a solution to most super-heavy vehicles. If you are taking Imperial Fist Chapter Tactics, you are missing out if you don’t include at least one squad of lascannon armed Devastators.
Centurion Devastator Squad
If normal Devastators are a little too static for you, Centurion Devastators are probably what you are looking for. They come with twin-linked heavy bolters mounted on their arms, which can be switched out for twin-linked lascannons to hunt tanks or grav-cannons to punish heavy infantry. They also have chest mounted hurricane bolters for dealing with light infantry, which can be switched to a missile launcher to add more anti-vehicle firepower. Doubling up on heavy weapons isn’t a problem for Centurion Devastators as Devastator Protocols allows each model to fire two weapons each shooting phase. Finally, you can give the sergeant an omniscope, which gives him both Night Vision and Split Fire. This is definitely worth it, as the firepower from even a minimum strength Centurion Devastator squad is overkill for most targets.
The most common configuration of Centurion Devastators is to equip the entire squad with grav-cannons. With 5 shots per model, these make the squad into a firepower based Deathstar. If you want to diversify the squad a bit, give the sergeant an omniscope, lascannons, and a missile launcher and use him to hunt tanks. This squad will play a central role in your army and will need to be large in order to absorb all of the firepower that will be directed against it. It is short ranged, so will have to be played very aggressively if you want it to earn its points on the table.
Alternatively, the squad can be armed with missile launchers and lascannons to take out tanks. Again, the sergeant can have an omniscope. You can either leave him with an anti-tank load-out and just use him to shoot another tank each turn or give him a grav-cannon to kill some infantry. This configuration also benefits massively from Imperial Fist Chapter Tactics. Twin-linked, Tank Hunting lascannons will rarely fail to damage their target (each shot has a 49% chance to damage even AV14. For comparison, a Tau Hammerhead’s railgun only has a 33% chance of damaging AV14). These squads can be smaller, even minimum sized, as they will usually be shooting at single vehicle targets and have the range to stay off the frontline.
Devastator Centurions bring massive firepower in a concentrated, durable, reasonably mobile package. You pay a lot of points for a squad, but used correctly, it will dominate the battlefield.
The Thunderfire Cannon is the stand-out infantry killer of the Space Marine Codex. It is an artillery piece crewed by a Techmarine with servo-harness (and only costs 25 points more than a standard Techmarine with a servo-harness). The Techmarine has all the usual rules, with the most pertinent being the ability to fortify a piece of terrain. He can still repair vehicles, though he’ll generally have better things to do with his shooting phase as long as the cannon is alive.
The cannon fires four blasts every time it shoots, and can choose to fire in one of three modes. It can fire a S6 AP5 surface detonation, which you will use in most circumstances. This mode will reliably put a lot of wounds on most infantry targets, and will even threaten Terminators if they’re tightly packed. It can also fire S5 AP6 Ignores Cover airburst, which you will generally use if your target has a better cover save than armor save. Finally, you can fire a subterranean blast, which is only S4 AP-, but forces any unit it hits to move as if in difficult terrain. If the target is already in difficult terrain, it will roll one less die than usual for movement. Vehicles count as moving through dangerous terrain. I find that this mode is the least commonly fired, and requires a seriously tough target. If the enemy has dangerous assault units, you can slow them down. If they have an important unit already stuck in difficult terrain, you can make sure they have a hard time moving out of it. It even gives the Thunderfire a means to damage heavy vehicles, albeit only through dangerous terrain tests. Special mention goes to hitting super-heavy walkers; they go from moving 12” to rolling 3D6 and choosing the highest. In the worst case, you just halved their movement. This is tremendously frustrating for an opponent running an Imperial Knight.
The Thunderfire Cannon is an excellent addition to a list running any Chapter Tactics. Its firepower and flexibility far outweigh its meager point cost. With 60” range and Barrage, it will always be able to target something important. I usually try to deploy it in fortified ruins, with good lines of sight. While it can fire indirectly, it is much more reliable when it has line of sight. Always deploy the cannon in front of the Techmarine; they are equally difficult to kill but the cannon is destroyed if the Techmarine is killed. If the cannon is destroyed first, the Techmarine can start running around and making a nuisance of himself.