Swordsmen vs. Nihilators, part 1, Math and Tough

This question pops up every once in a while on the Skorne forum:  Which infantry unit is bettter: Max Praetorian Swordsmen with UA, or max Nihilators?

My position has sort of been that they're both about equally good at doing pretty much the same job.  I mainly use infantry for jamming and screening, either to protect my warbeasts and warlock from opposing threats, or to keep enemy infantry from protecting their most valuable targets from my threats.  Both Swordsmen and Nihilators are good at killing whatever enemy infantry they've been sent to counter, and they're both underwhelming at damaging whatever 'beasts or 'jacks they've been sent to jam.

Rather than dig into every factor which might influence battlefield performance just yet, I'm going to look at Tough.  Nihilators have Tough, and Swordsmen don't.  Tough is a pretty significant advantage, particularly for a unit which is mainly around to occupy space and soak up damage, like Nihilators and Swordsmen.  It amounts to a 50% increase in durability over a similar unit (comparable body count, Def and Arm).  In terms of actual numbers, it takes 15 damaging hits on average to wipe out a 10-strong unit with Tough (Tough stopping 1/3 of the incoming hits), and only 10 hits to wipe out a comparable unit without Tough.

Swordsmen are pretty comparable to Nihilators.  Both units have the same Def.  Swordsmen have one more point of Arm, but this advantage is at its most significant against Power 6-8 hits* (average for blast damage, otherwise very low), and isn't much of a factor against Power 10-12 hits (average for most attacks).  The only complication comes from the Swordsmen UA, which adds two bodies to the unit.  Statistically, this goes a pretty long way to closing the gap.  Even assuming that the Swordsmen officer is killed in one hit (in my experience it's just as likely to take two), the Swordsmen will take 12 hits to finish.  In terms of relative durability (admittedly a far less useful way to look at it), the Nihilators' advantage is halved, to 25%.

Is 3 hits (or 25% depending on how you look at it) a significant advantage?  Yes, very much so.  Attack output is a valuable resource in Warmachine/Hordes, and sometimes it's hard to find the resources to hit a single unit 3 more times (which of course takes more than 3 attacks, since you need to roll to hit as well).  Sometimes, even when the attacks exist, it isn't worth it to divert them from other goals.

So Nihilators have a significant natural advantage in durability over Swordsmen, but of course, this can be offset by support.  Spells and abilities (like Hollow, for example) which grant Tough, give Swordsmen the advantage.  Anything which decreases the number of damaging hits the unit takes (anything which boosts Def or Arm, in other words) will decrease the overall impact of Tough on a game.  The fewer hits a unit takes (or the less often those hits cause damage), the fewer Tough rolls will be made, and overall, fewer models will be saved by Tough who would have died otherwise.  Skorne has a lot of options when it comes to boosting Def and Arm.  Defender's Ward (which is the spell I'm most familiar with) does both, for example, making Swordsmen and Nihilators a little more equal in durability than they would be otherwise.

Of course, looking at the total number of hits a unit can take might not be the best way to view the impact of Tough on a game.  Often, an opponent will want to kill just a few models in a unit to open a path to something that unit is screening, and in that situation, Tough is at its most valuable.  The Tough models will always be able to take 50% more hits than non-Tough models, and some halfway decent rolling might just save your warlock.

So those are my thoughts on the Great Debate for now.  Slight advantage to the Nihilators, but it can be reduced by defensive abilities.  More thoughts on this later.

UPDATE:  Michael pointed out that I neglected to mention the offensive side of Tough.  Any Nihilator who survives a round due to Tough is probably going to be on the front lines, ready to make attacks.  This can be a big advantage against an opposing infantry unit (Nihilators are more powerful offensively against infantry).  Tough can let a player use any surviving models to do damage to the enemy unit rather than devoting other resources to getting past it or holding it up.  If there's a Tyrant Commander handy, the Nihilators can be affected by Reveille, and move into better positions before attacking.

*A Pow 6, 7, or 8 hit will need to roll an 8, 7, or 6, respectively, to damage a Nihilator, whereas it will need a roll of 9, 8, or 7 to damage a Swordsman.  Statistically, 6, 7 and 8 are the most common rolls on two dice, accounting for almost half (16/36) of all possible rolls.  When any of these rolls accounts for the difference between a model living and dying , the effect of whatever caused the difference (like that 1-point difference in armor between Swordsmen and Nihilators) is at its most pronounced.

As an aside, these are also the numbers I use when determining whether something will hit reliably, or be missed reliably.  So needing 6's to hit is pretty reliable, at a probability of 26/36 (about 72%), and being hit on 9's is pretty safe, since you'll only be hit 10/36, or 28%, of the time.