So has anyone here come up with rules concerning damage to armor over time? Like a staged penetration? Where over time the armor as it's breached becomes less effective and it's armor value goes down.

I was thinking of tieing it into righteous Vengence. Where if an attack breaches armor and a nat 10 is rolled on the damage dice, and it breaches the armor. The locations armor value is reduced by one.

Thoughts? Opinions?

Yeah, I spent some time pondering over this as well. There's a ton of options you could try here, the natural 10 being one of the most obvious. But it really depends on how often you want this to happen, and how "realistic" you want to keep things - a natural 10 might occur more often and extend to low-powered weapons, whereas a minimum amount of general damage (factored against an armour-dependent "Resistance" characteristic) sounds more realistic but, depending on how high you set the threshold, might only occur on some weapons, or even be guaranteed with them. Realistic, but not necessarily fun.

Another possibility would be to track the total damage done to the armour like a second Wounds score, and deduct AP when certain thresholds are reached. Needless to say, however, this slightly increases the amount of stuff that needs to be written down.

The damage type might also play a role; perhaps Explosive damage has a greater chance to trigger armour degradation than Energy? Based on your suggestion regarding the natural 10, an Explosive attack could trigger on a 9 as well as a 10. On the other hand, flamethrowers might be required to actually confirm the Righteous Fury in order to melt something off the suit.

Regardless of how you do it, I'd never make a suit of armour completely worthless, but limit degradation to, say, 50% of the original value. So even the most hole-ridden suit of powered armour would still grant at least 4 AP. Patching up could be done with repair cement in the field (restores 1 AP, does not stack), or, obviously, back at the base for a full repair. It's also an opportunity to involve your Squad's Techmarine, if you have one.

While immortal armor isn't very realistic, it is far easier on the gaming side. Less numbers to track and to worry about. You're supposed to be an over the top super hero....and that feeling gets lost when you see your armor is at half.

Unless you're running a low supply campaign where they're going months without resupply and you expect them to run out of bolter rounds, I'd skip this.

I save this kind of thing for Critical Hits caused by powerful weapons, meltaguns lascannons etc, particularly where a fate point has been burned. So the armour absorbed the attack but was very badly damaged in the meantime (say takes d5 points of damage) in addition to any injuries the marine suffers in surviving the attack.

I think if you introduced a more general rule for recording damage to armour it would slow the game down something awful and it is not really thematically fitting for marines to have their armour shredded to this extent. Immortal armour isn't realistic but it is thematic with the game.

The occasions where significant armour damage occurs to marines are specifically noted. It does occur to a notable extent in the Horus Heresy, particulary for marines who fought on Isstavan which was one of the bloodiest battles of the campaign.

I think if you introduced a more general rule for recording damage to armour it would slow the game down something awful and it is not really thematically fitting for marines to have their armour shredded to this extent.

At the same time, there are numerous artworks of Marines with fist-sized chunks blown out of their chestplate by bolt explosions - it signifies an act of defiance under fire, and I'd say this is very fitting for powerful characters in 40k.

I certainly agree about any additional rules in this regard having a risk to slow the game down, but perhaps some day, someone will have a great idea.

A quick and easy way to do it would be that if a location suffered a hit that did (after accounting for cover, but before accounting for armor or toughness) more than double the armor value of that location in damage, it reduces its protection by 1.

When faced with environmental hazards (such as the inside of a tyranid ship, or walking through lakes of acid), you can set thresholds for the time of exposure (based on the severity of the hazard) before the armor value of the exposed locations is reduced by 1. If, for example, you had set the exposure time for strong acid to be 5 rounds, and they leave a lake of said acid after 3 rounds, then cross back through it, entering it for 3 more rounds, the armor of any locations actually submerged in the acid would be reduced.

Doing this can make people exceedingly nervous, and rightly so. Dramatically and thematically it's great, but be exceedingly cautions when doing so- as combat is balanced around full armor values, it can get much more deadly, *quickly*, using these rules. I would recommend allowing a Tech Marine to use Tech Use to restore 1 point of Armor Value (max full, of course), in a system much like the Apothecary and Treated Wounds- if armor is reduced by 1, it can be treated, then if reduced by 1 again, it can be treated again, but if reduced by 3 before being attended to, after treating it once (getting it to -2) it cannot be treated again until it is reduced again, to represent the damage going from cracks to fist sized chunks missing, and there only being so much you can do on site without access to the forges. You could even allow the Tech Marine to take an elite advance, or requisition a special piece of wargear, that allows it to be improved by 2 points when treating it.

Finally, any rules that allow armor to be reduced during the course of the mission would synergize very well with rules that allow marines to improve their armor. In our campaign, Rogal Dorn allows people to use requisition for a mission to improve armor. Each location can be improved by 1 point (30 requisition, requires respected), and after being improved, can be improved a second, final time by an additional 1 point (45 requisition, requires distinguished). While your armor is being upgraded, that piece is replaced by a piece of "stock" armor (so you lose any upgrades already done, or other benefits you have associated with that location), and as it is being cobbled together with unfamiliar components, your machine spirit is angry, denying you any benefits from your armor history. Since he also uses an armory system (which I think is awesome, read more here http://community.fantasyflightgames.com/index.php?/topic/110538-the-armory/ ), we only get around 20 requisition per mission each, to do things like this, or obtaining cybernetics, or assets. As a result, people must work together and share requisition to upgrade armor at all.

Personally, I would be looking for a way that also allows weaker weapons to damage heavy armour by sheer volume of fire - this is, I suppose, the biggest problem, and I fear abstraction cannot be avoided. Perhaps rolling a "10" on the damage die might have this effect? It's a 10% chance, which actually feels a bit too much, but on the other hand each suit of armour has several points of armour that could be whittled down to a minimum rating (half the original AP?)...

I do like your idea on environmental hazards though, as well as the upgrade rules!

I had planned something similar, just with modular pieces of plate you'd basically tack onto the existing armour, and only a single version per location. It was inspired by the items from DoW Soulstorm's HQ customisation.

You could use the rules for degrading cover. Any damage over the armor rating reduces the rating by one. Which makes it pretty brutal when you think about it.