I thought we'd talk a bit more about the Thunderfire cannon after a couple comments back and forth in Vt2's recent review post. This post will be akin to my Tau review posts currently and offer up suggestions on how to fix the Thunderfire as well as taking a peek at how it works. So, the Thunderfire is quite impressive in the amount of damage it can do to infantry and its utility to offer up different type of shots. Unforunately, all of these shots are designed as anti-infantry with low to medium strength and some cover busting potential. Whilst it can also cause difficult terrain checks to anything it hits (great for parking lots and bikers), it is and always will be currently, an anti-infantry gun. This isn't really bad and although it would be nice to have some sort of anti-tank shot, the real problem lies in its fragility.
Although the Thunderfire cannon has a good range (60") and should set up with at minimum a 4+ if not 3+ cover save thanks to the Techmarine's special ability, once anything gets through that cover save and actually "hits" the cannon, the Cannon is likely to die and if one has a lot of infantry or large amounts of infantry in tanks, this will generally happen pretty quickly. This makes the Thunderfire Cannon a glass cannon. It can do a lot of damage but can't take it. Whilst this is fine in some armies (hi DE!), Space Marines generally work around durability. Although the Thunderfire is pretty cheap for it's offensive prowess against infantry, in 5th edition and the SM codex where they don't really fit into the style of army they promote, the Thunderfire rapdily slips down the ranks of usefulness when compared to the Predator and Land Raider.
So, how to make it better? Easiest way to fix it is to fix the Artillery rules. No longer is a pen/glance = destroyed but force the opponent to roll on the table and on a 3/5/6 it's destroyed (or 4+), etc. Make it more durable without having to give it an armor value is a big step towards making this gun viable. Giving it more crew members or simply making it a tank of some description removes some of these issues as well. This is not just specific to the Thunderfire Cannon but most artillery pieces. Providing a 4th shot type as well could help it against tanks. AP1 is the obvious answer but you could also give a low strength shot 2D6 to pen or remove blast completely. However, even with a couple of these changes the Thunderfire isn't going to be a mainstay in SM armies unless their codex changes as well. As it stands, SM puts a heavy emphasis on full ,or nearly full, mech armies unlike BA/SW/IG. This will make the Thunderfires stick out and ad a very immobile element to the army not to mentioned potentially have LoS issues (though deplyoing on higher ground *cough ruins cough* alleviates this).
There is certainly potential there. No one likes a bunch of S6 blast templates dropped on their clumped guys but not fitting into the codex or ruleset edition and being very easy to destroy makes the Thunderfire Cannon need a bit of an improvement before it becomes more useful.
