Now that Thunderfire Cannons can be taken in batteries of up to three TFCs each and gain BS6 for their Techmarine Gunners if they have a full battery of 3 artillery peices (as per the “Convergent Targetting” rule), they are significantly more accurate than in their old iteration from the 6th edition Codex: Space Marines.
Specifically, a battery of three TFC can put out 12 Small Blasts per shooting phase, all at BS6, which means that the average scatter is 1″ and the max scatter is 6″. Combine this with the versatility of the firing modes available (TFCs are basically the Sternguard of the Heavy Support section in the Space Marine book) and the relatively low cost for each artillery piece (only 20 MBs each, or 60 MBs for a battery of three TFCs) and what was a competive unit in the old book is downright super-charged in the new codex.
To take this to an even more potent level, imagine a battery of three TFCs supported by a nearby Land Raider Excelsior. The Land Raider Excelsior, in addition to having a Grav cannon/Amp replace its Heavy Bolter and a 6++ save, is basically a normal Land Raider with the ability, once each Shooting Phase, to confer a special rule on a friendly unit from the same faction within 12″ of it (or 18″, if you buy the correct upgrade). The special rule can be chosen from the following list:
-Hit and Run
Regarding the TFC battery, the first three on this list (Counter-attack, Hit and Run, Skyfire) have limited to no use for a TFC, which should not be in close combat and cannot shoot at Flyers/FMC because it is a Blast weapon.
Fearless can be useful to ensure that the TFC battery doesn’t run/continues shooting/holds objectives and Split Fire has good utility in allowing the battery to engage two separate targets and not waste its considerable firepower on overkill for a single enemy unit.
The real stars, however, are Preferred Enemy, Tank Hunters, and Interceptor. Let’s take a look:
1 – Preferred Enemy — When used in conjunction with the Surface Detonation mode of shooting (S6 AP5), this can incredibly devastating to massed Guardsmen, Gaunts, Orks, Cultists, Tau Pathfinders, etc. With AP5 ignoring their armor and wounding on 2+s, Preferred Enemy gives them re-rolls of 1s to Wound, meaning that almost every hit translates to an Unsaved Wound. With 12 Small Blasts and BS6, the TFC battery should get quite a few hits, especially against a tightly packed horde formation. Even against MEQs this shooting should cause a very high number of wounds, forcing a lot of 3+ saves and grinding down even troops in Power Armor. If you are going up against light troops in cover, then switch to Airbust firing mode (S5 AP6) and, combined with Preferred Enemy, you should have an equally potent effect on whatever the TFCs target.
2 – Tank Hunters — While most people do not think of the TFC as an anti-vehicle unit. with 12 x S6 blasts and high Ballistic Skill, a battery can threaten light to medium armor reliably. Throw in the Tank Hunters USR and suddenly TFC batteries become a genuine danger to anything with AV12 or less. Imagine a TFC battery targeting a Wave Serpent or a Chimera or a Dreadnought. With BS6, the TFCs would likely get about 10-11 hits. Glancing on 6+s, with re-rolls from Tank Hunter, that translates into 2-3 HPs stripped, which enough to critically damage our outright destroy any one of these targets. Against less armored targets, like Rhinos, DE Raiders, Eladr War Walkers, Tau Pirahnas etc etc., then TFC shooting with Tank Hunter becomes even more dangerous.
3 – Interceptor — Perhaps the best rule to use with a full battery of TFCs, this gives Space Marines the ability to combat deep striking enemy threats that would otherwise be unstoppable until at earliest the next player turn. Imagine a squad of Eldar Wraithguard ith D-Scythes DSing in with a DE Webway Portal. Normally, the only defense against this is “bubble-wrapping” your important units and deployment shenanigans. With TFCs at BS6 and having the Interceptor USR, you can potentially get as many as 25-30 hits on a DSing Wraithguard unit (remember, they have to be bunched up when they come in, per DSing rules)… at S6 vs T6, this translates into 12-15 wounds, with the Wraithguard failing about a 1/3 of their armor saves, resulting in an average of 4-5 dead Wraithguard. While this might not be enough to completely kill the unit and prevent them from unleashing their D strength templates on your army, it can eliminate a signficant portion of their combat power, allowing them to be destroyed easier later on and also lessening the impact of their shooting on your forces.
In summary, you can see how well a Land Raider Excelsior combines with a TFC battery (by the way, the TFC Techmarine Gunners can still Bolster Defenses for terrain in your DZ and, in a pinch, repair your vehicles if they can’t shoot their cannon that turn). While not a cheap option, taking a TFC battery of 3 artillery pieces and Land Raider Excelsior (and a Rhino Primaris as well, since you have to have one when taking a LR Excelsior; they come as a singel HQ choice) provides a versatile and deadly “firebase” battle group for your army.