How does armor penetration work?

[TheLunaticist]

I recently noticed that the main reason why my APS's do so little damage is because the shells armor penetration is so low.

I searched for it, but no explaination is understandable from my poin of view.

What is armor penetration?
What is health?
When does a bullet penetrate armor and when not?
Is armor penetration only how much armor the shell penetrates, or also how much damage it does?
If question above true, how much does armor penetration affect damage?

[Silamon]

No clue about the exact numbers on armor penetration, but the way it works is armor has an armor class value. Each block has an armor class value listed, and layered blocks will gain a certain percentage of extra AC from the blocks behind it. High AC will significantly lower the effective damage of a shell hitting it. There is a tool you can equip that will let you see the armor class of layered blocks to see how tough the armor actually is as well.

On shells you have 2 important values for ap damage, first the ammount of Kinetic damage it has, and the armor piercing value. The higher the armor piercing value a shell has the more easily it can deal damage to blocks with a high armor class, but you still need enough kinetic damage to destroy the block or you will not pierce the armor.

So basically, you can pierce armor with high kinetic damage and low armor pierce, but you will do it much easier with a higher armor pierce value.

[Alcates]

All blocks have Armor Class (AC) and all weapons have Armor Penetration (AP) The effect this has on damage has nothing to do with "how much armor the shell penetrates" but rather a damage multiplier. If the AP of your shell is exactly double the AC of the enemy armor, it does full damage, meaning it simply subtracts the shell damage from the block health. If the AP is less than double the AC, it does less damage than it says. I'm not entirely sure if overpenetration increases damage.

There are factors to be taken into consideration such as armor stacking. (A two meter thick metal sheet has double the surface AC of a single layer.)

[Silamon]

As far as armoring your ships goes, when you are doing layered armor you want the blocks with the highest health to be the first layer too, because once the first layer is gone the second layer will have less armor class than the layered armor did and will thus be much easier to get through.

Say for example you built a wall with 1 meter of metal and 1 meter of heavy armor. Either way you put them, it will end up with a similar AC value on the first layer. But if you put the heavy armor at the front you will have significantly higher HP to go along with the AC on the first layer, so it will last longer against damage than it would if you had put the metal at the front.

Edit: as far as building APS for armor piercing shells, you probably want a fairly high caliber, at least 300mm or so. Anything smaller you would be better off with other shell types like hesh/heat or frag rounds.

[FourGreenFields]

The wiki-page for damage is actually up-to-date for the most part. https://fromthedepths.gamepedia.com/Damage
(Parts about EMP and lasers is still unchecked, and it's probably (1- cos(theta))^AP/AC (not ^2AP/AC), but it's usable)
Note that most of the rest of the Wiki is not up to date. I want YOU for the FtD Wiki!
(If you actually want to help the wiki, I'd recommend the #ftd_wiki channel on the official Discord)

Originally posted by TheLunaticist:

What is armor penetration?

Sets an effective damage multiplier of min{1, AP/(2 * AC)}, so max damage is achieved when AP >= 2 AC, and linear damage reduction below that.

Originally posted by TheLunaticist:

What is health?

Pretty much same as in most games. 1 Damage = 1 health lost (at effective damage multiplier of 1), 0 health = block destroyed.

Originally posted by TheLunaticist:

When does a bullet penetrate armor and when not?

When it has the damage to destroy all blocks in its path.
Exception are HEAT and HESH. Allthough, technically, it's not the shell that penetrates. Those use the sum of square roots of the ACs, which needs to be smaller than penmetric/spalling-metric.

Originally posted by Silamon:

Edit: as far as building APS for armor piercing shells, you probably want a fairly high caliber, at least 300mm or so. Anything smaller you would be better off with other shell types like hesh/heat or frag rounds.

Probably not. A single low-calibre AP-shell may not pierce, but it'll still do damage. Low-calibre HEAT will generate very few fragments, and low-calibre HESH may even fail to spall alltogether.

Low-calibre frag, on the other hand, is a good choice. Probably the only other choice apart from AP.

[Silamon]

Well 200mm would be the lowest I would go on hesh/heat. Wouldn't those shell types still do more than solid AP vs layered metal at 200mm?

[FourGreenFields]

Originally posted by Silamon:

Well 200mm would be the lowest I would go on hesh/heat. Wouldn't those shell types still do more than solid AP vs layered metal at 200mm?

I'd consider 20cm about the lowest for HEAT and HESH too (allthough HEAT may also work at about 15cm, but it'll be easier to counter then).

And, as so often, it depends. Layered with proper spaced armour + spall-liner, I'm reasonably sure you want AP or hollow-point (or frag). Without spacing, or with poor spacing, the result might be different.