Friday, February 25, 2011

In Defence of the Heavy Venom Cannon

So I've heard a lot of talk about how useless Heavy Venom Cannons are. Let's talk about that. First of all, they ARE improved from their incarnation last edition. I hope everyone caught that. They ARE capable of destroying a vehicle on a pen, which is a bonus.

For the uninitiated, the Heavy Venom Cannon is a 36 inch range, Strength 9 AP 4 Small Blast Assault 1 weapon. Sounds pretty good right?

Well, the drawback is that against non-open topped vehicles it gets -1 to the vehicle damage roll.


Well, it is if you are using your Heavy Venom Cannons to kill tanks. That's not really what I plan to use them for in most cases.

Let's take a moment to do some maths around this topic. You all know how I love maths. If you have been following along with my little mini-series on basic Warhammer Probabilities, most of this shouldn't be new to you. After all, we are just doing a simple weapon damage calculation.

The tricky part is that this is not a "normal" weapon, but is instead a blast. And while calculating how likely a blast is to "tag" a single infantry model is very easy, calculating the probability that the center hole of a blast will land on a roughly rectangular shaped vehicle is quite hard.

It requires quite a bit of trigonometry, data tables, and some pretty extensive Excel spreadsheets to get some good numbers. But I, being me, did in fact build that tool (sadly the original spreadsheet no longer exists but you can find the data I got from it here). The results are largely pretty unremarkable, a shooter with a given ballistic skill will hit roughly as much as he would if he were firing a normal weapon (so BS 3 is about 50% hit ratio, BS 4 is about 60%). Especially true if the firer is BS 3. So for the purposes of our calculations I'm going to assume a 50% hit rate.

The nice thing about scattering weapons of course is that if they miss their target they still might hit something else... but it's really difficult/impossible to quantify such a thing so we can tuck it into the "nice bonus when it happens" category (which, as you will see, is where the "destroyed a vehicle" result is going to go too!)

Ok, so armed with that info we can do a basic probability table. But first we need to know what our goal for the weapon system is.

Well, like most things, it can be used in multiple ways. But what do we need in a Tyranid list more than ANYTHING else?

Vehicle Suppression.

Am I wrong on this? It seems to me the lists that Nids are going to REALLY struggle against are going to be heavily mechanized shooty lists packing AP 2/1 weapons. Plasmaguns and Meltaguns concern me, but they have to be within a pretty close distance to use those. What REALLY worries me are Lascannons, Dark Lances and vehicle mounted Plasmaguns/Multimeltas (that can move and shoot).

Those weapon systems can simply force cover saves on you all day long with nothing you can do about it except cry.

When you have no answer to several of the very popular and very good lists out there (Razorspam, Raider/Ravager Spam, Mechguard) other than "die in a cinematic fashion" you are not playing a take all comers list that's capable of winning tournaments with any regularity.

Do we agree?

So we need to suppress some of that incoming firepower. And we need to be able to do it at range, because the really dangerous stuff can shoot us from outside 24" and move away. So TL Brainleech Devourers, while pretty cool, don't seem to fill this role.

So how effective will our Heavy Venom Cannons be at their appointed tasks? Well, let's see.

Shooting at a Razorback, we have a (1/2) chance to hit and a (2/3) chance to pen. After we pen we really would like to see any of the following results:

Shaken - no shooting is good.
Stunned - no shooting and no moving is better.
Weapon destroyed - always take the Lascannon to force them to come into range of your Hive Guard. Good result but not the best.
Immobilized - an ok result but not what I was going for.
Wrecked - Yeah baby.
Exploded - Impossible against a Razorback.

The odds of us getting those results are slightly different because of the -1 on damage table thing, so we get

Shaken, 2 out of 6
Stunned, 1 out of 6
Weapon Destroyed, 1 out of 6
Immobilized, 1 out of 6
Wrecked, 1 out of 6

So anything except for Immobilized is probably going to shut down shooting for the turn. so 5 times out of 6.

So final results for the pen are (1/2) x (2/3) x (5/6) = 27.8%

Now we need to find the glance results too. I'll summarize this a bit:

(1/2) to hit x (1/6) to glance x (6/6) to suppress. That's right, anything I roll on a glancing table will be good for me, so I'll count them all, shaken, stunned or weapon destroyed.

Final results are (1/2) x (1/6) x (6/6) = 8.33%

So we add the 27.8% to the 8.33% for a grand total of 36.1% chance to suppress a Razorback per shot fired. Now I don't know about you guys but to me, that is valuable.

Let's talk about the other bane to Tyanids existence: the Ravager. This is a vehicle that can EASILY outrange our Hive Guard. T-fexes lend a good deal of punch at taking these down, but if I know I really need to suppress/destroy three targets, do I really want to be shooting with only two sets of guns?

For the sake of this calculation I will assume the Ravager is hiding behind Raiders to get cover. I think that's a safe bet. I would rather shoot at a Ravager in cover than a Raider in the open if the Raider has a 5+ Flickerfield save and only one gun, whereas the Ravager has three guns and a save that is only marginally better.

So while I don't know the exact dimensions of a Ravager for the moment I'm just going to assume the same 50% hit ratio, which is pretty safe I think.

(1/2) hit x (2/3) pen times (1/2) cover save equals 16.66% chance to get a pen through. Not fantastic, but reasonable.

Remember that because Ravagers are open topped, not only does the Heavy Venom Cannon not suffer the -1 to the damage roll, but we also get an additional +1 to the damage roll from the Open Topped rule.

So from the pens we have a damage chart that looks like the following:

Weapon Destroyed

Yikes. Not good for the Dark Eldar player. So again 5/6 of these results are good for us. We don't really care about Immobilized results as much, other than they will allow us to get our Hive Guard in range.

So in the end we have about 13.9% chance to do something good against a Ravager, even if it's in cover.

Oh, let's not forget about the glances. So that's (1/2) hits x (1/6) glance and again 5/6 results are good for us, so a total of another 3.5% when we factor in cover. Add that to the original and we get 17.4% total per shot.

Not fantastic, but not awful either. Remember that the goal here is to suppress shooting, not necessarily destroy the enemy vehicles outright (though if it happens, great). Keep in mind also that if we catch that Ravager without cover the odds go up.

The HVC also pulls reasonable double duty as anti-infantry. Particularly nice against deep striking Blood Angels with Feel No Pain (which it ignores). Not to mention that it's nice to put multiple insta-death strength hits into certain units as well, to keep Independent Characters from sucking up wounds, for example.

So is the Heavy Venom Cannon worth taking? To me it is. It's not a replacement for the 'real' can openers in the army, but it's a nice supplement, and when looking at this versus the TL Devourers, the range is a really big factor for me.