When looking at vehicles they tend to have a similar amount of wounds to trooper units and generally worse armor saves, which is confusing since they are supposed to be durable war machines. The Armor keyword however makes all the difference, ensuring that the vehicle ignores all wounds it takes that aren’t critical. We know that every die has a 12.5% chance to roll a critical, or 25% chance if it also surges to critical, which means that Armor greatly reduces the amount of damage that can even affect an armored unit. However, how much work is wasted when shooting at an armored unit compared to a non armored unit?
First we have to know how many successful sides of a die armor turns from a success to effectively blank:
- White Dice: 1 hit, 1 surge, 1 critical - or cancel 50% of successes with no surge, 66% of successes with surge to hit, and 33% successes with surge to critical
- Black Dice: 3 hits, 1 surge, 1 critical - or cancel 75% of successes with no surge, 80% of successes with surge to hit, and 60% of successes with surge to critical
- Red Dice: 5 hits, 1 surge, 1 critical - or cancel 83.3% of successes with no surge, 85.75% of successes with surge to hit, and 71.5% with surge to critical
If we average all of those cancelation percentages out we find that on average a unit with armor can expect to negate about 67% or 2/3 of successful hits out of any random assorted die pool. This makes the Armor key word incredibly strong in terms of increasing a units survivability.
Using these numbers we can also learn how best to deal with Armor. Looking at the cancelation percentages we see that white dice that surge to critical are the most efficient dice to use against armor - in other words you will be wasting the least amount of work that could be going towards another unit. Conversely red dice that surge to hit are the worst dice you could put into Armor because they could be doing a lot more damage against another unit.
Using a real world example lets look at an AT-RT with a rotary canon shooting at a unit with armor - we know from the Never Tell Me The Odds article that the AT-RT would expect to get 1.25 critical hits against armor, we also know that shooting the same weapon at an unarmored target we would expect to get 3.125 hits, meaning that the AT-RT is losing 60% of its work to Armor. If we do the same math with a 5 man Rebel Trooper unit we find that they do 0.625 damage against armor compared to the 2.5 we would expect them to do normally making it an incredibly inefficient shot wasting 75% of its damage. General Veers with an aim token on the other hand is incredibly efficient at damaging vehicles, he normally is expected to get 1.8 damage while against armor he gets 1.3, only slightly reducing his expected output.
Impact is the keyword given to anti armor guns such as canons and missiles. In game mechanics Impact X turns X number of regular hits into criticals when attacking a unit with Armor making some weapons more efficient against vehicles than others without bloating the number of dice and balancing how much damage a weapon can do to a vehicle vs a troop unit. In terms of calculating expected damage of Impact vs Armor the simplest way is to look at a die pools expected damage output, subtract the Impact value from that number, and then add in the remaining dice with their normal chance to roll a critical. Lets take Speeder Bikes as an example: they roll 2 red, 2 black, and 2 white with surge to hit and Impact 2. They are normally expected to do 3.75 damage against units without armor, against units with armor we will remove the two red dice and a white die to get us to 2.125 (or just over what our impact number is), this leaves us with two black and one white die which we can add back in to our total as their normal chance of critical giving us 2.375 which is our expected damage vs armor.
To give one more real world scenario we will use the AT-RT rotary canon and AT-RT Laser Canon. The rotary canon has no impact and 5 black dice that surge to critical, meaning that we simply add up all the dice as their regular chance to crit or 1.25 damage. The AT-RT Laser Canon on the other hand rolls two black and one red die and has Impact 3, since it has the same number of dice as it has Impact we cant use the spare dice to round up our expected damage nicely and instead simply use the normal expected damage of the dice or 2.125 - similarly for impact grenades, since every model contributes Impact 1, we simply use the total normally expected damage to figure out the expected damage against armor.
Using these numbers we now have a much better understanding of how the Armor keyword affects the survivability of the units that have it and how to best prioritize which weapons to employ against them. And generally should be in this order
- weapons with Impact X
- white dice with surge to crit
- white dice with no surge
- white dice with surge to hit
- black dice with surge to crit
- anything beyond this is generally considered too innefficient and should be dedicated elsewhere