So, I was a little bored at work today and a probability question has been bugging me for a while. What is the probability of killing Necron Warriors when they have a 4+ save, followed by a 4+ RP (Decurion) and re-rolling 1s due to the warlord being within 12 inches. The re-roll RP (Resurrection Protocol) rolls of 1 had been the bit that I was stuck on. So today I did some calculations on a spreadsheet to work things out.

TL DR, it takes approx 13 shots from a marine with a bolter to kill a warrior. Without the re-roll of 1s, it takes approx 12 shots to kill a warrior. Doesn't sound like much of a difference, but when you have a big blob of 20 warriors the maths looks a little more impressive. It takes approx. 262 bolter shots to kill all 20 warriors!!!! That is insane! Without the re-roll of 1s it takes a mere 240 shots. I suppose its still not a huge difference. The main point is that it takes an insane amount of shots to kill Warriors in a Decurion detachment. When you add in things like 3+ saves on Immortals or 3++ saves with RP on Wraiths you're in crazy territory. I haven't worked out the maths for that. Maybe tomorrow.

For anyone who cares here is the maths that led me to this.

Marine with bolter (or necron warrior) vs Warrior in Decurion.

Marine BS of 4, 2/3 shots will hit.

Strength 4 vs Toughness 4, 1/2 of hits will wound, so its now 1/3

4+ save, so 1/2 of saves will fail. So we're now at 1/6

4+ RP roll, so we're now at 1/12 shots will kill.

Now it gets tricky with the re-roll of 1s. 1/6 of failed RP rolls will re-roll, this is 1/24 of the shots fired. 1/2 of these will actually pass their re-rolled RP roll. Thats 1/48 shots will pass a re-rolled 1 RP roll. Adding 1/48 for the failed re-rolls to the.... oh damn my notes have failed me, I can't remember how I got to the next hurdle but I have 11/48 x 1/3 written down and I can't remember why now. I came to the answer of 11/144 chance of killing a warrior or 13.09 shots to kill it, which makes sense given the calculation below without the re-roll.

The maths for without the re-roll is a lot easier.

Marine BS of 4, 2/3 shots will hit.

Strength 4 vs Toughness 4, 1/2 of hits will wound, so its now 1/3

4+ save, so 1/2 of saves will fail. So we're now at 1/6

4+ RP roll, so we're now at 1/12 shots will kill.

Or 12 bolter shots to kill a warrior. 240 bolter shots to kill a blob of 20 warriors.

Without Decurion

Marine BS of 4, 2/3 shots will hit.

Strength 4 vs Toughness 4, 1/2 of hits will wound, so its now 1/3

4+ save, so 1/2 of saves will fail. So we're now at 1/6

5+ RP roll, so 2/3 will fail, we're at 2/18 or 1/9.

So it takes 9 bolter shots to kill a warrior not in a Decurion instead of 12. Makes quite a difference. Only 180 shots to kill 20 warriors (lol) compared to 240.

With guardsmen with lasguns against decurion warriors you may as well pack up and go home. To kill 20 warriors (without re-rolling 1s) it takes 480 lasgun shots! 24 shots to kill just 1 warrior.

I will try tomorrow to get the missing bit of math for the re-rolls. The end answer is still correct I believe, I just can't remember how I did the last bit of calculation.

I think the lesson to learn from this is don't bother trying to kill warriors with bolters because you will be rolling dice all day. The Decurion adds quite a chunk of extra resilience to and already resilient army for only the cost of loosing objective secured and being forced to take particular units. I don't think its much of a tax and having wraiths with a 3++ and a 4+ RP roll with 2 wounds at T5 is just plain wrong.

Like with any math-hammering and with my dice and rubbish dice rolling hands this will probably fail to stand the test of real life (real life toys anyway) battles.

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