You already know, from the previous episodes of How it Works,
how armor-piercing shells deal damage.
But in order to deliver their harmful payload to a ship's vital compartments,
they need to penetrate the armor first.
In today's episode, we're going to talk about how the armor works,
and how to penetrate it the right way.
How It Works
The velocity of a shell, its mass,
and the shell to armor incidence angle affect armor penetration.
However, a ship's armor is a complex multi-layered system of armor plates.
The multi-layered armor structure
is the primary feature of the armor in World of Warships.
Now let's demonstrate this with an example.
New York fires an armor- piercing 356-millimeter shell
causing 10,000 damage to the side of Fuso from a distance of 18 kilometers.
The armor penetration of this shell at such a distance is 204 millimeters.
At the point of impact, the shell will meet 19-mm antitorpedo protection,
a 203-mm casemate armor belt, and finally, a 99-mm citadel armor deck.
In total, 321 millimeters.
When a shell hits armor, several checks are made.
The first of them is the 14.3 caliber rule.
If the armor is thinner at the impact point
than a shell caliber divided by 14.3,
then the shell won't ever bounce off the armor,
regardless of the angle of incidence.
Then, the penetration check starts.
The antitorpedo protection, of course, doesn’t stand a chance.
But these 19 millimeters did their job
and reduced the armor penetration of the shell.
204-19=185.
All the checks have to be done again for each of the following armor layers.
The 14.3 caliber rule doesn't work with 203 millimeters.
Next, the second check applies, the ricochet calculation.
If the incidence angle is from 0 to 30 degrees, it's 100% a ricochet.
If the incidence angle is from 31 to 45 degrees,
the probability of a ricochet is reduced.
And, finally, if the incidence angle is from 46 to 90 degrees,
a ricochet is practically impossible, and the armor penetration check starts.
By the way, we should note that British cruisers
and American 203-millimeter cruiser guns have sharper ricochet angles—
ricochet is impossible even at 30 degrees.
New York's shells have two possible future outcomes:
if there is no ricochet,
then the remaining 185 millimeters of the armor penetration,
left after the shell goes through the 19 millimeters of antitorpedo protection,
won't penetrate the 203 millimeters of Fuso's casemate armor belt.
The shell will detonate and it won't do any damage,
because the explosion occurs in the antitorpedo protection
that is specifically designed to prevent damage to a ship.
The second outcome:
the shell hits Fuso's side at a sufficiently sharp angle, bounces off,
then, hits the 19 millimeters of antitorpedo protection again,
penetrates it according to the 14.3 caliber rule, and falls into the water.
Now, let's place New York closer and fire a shell from 15 kilometers.
The armor penetration at such a distance is 224 millimeters.
[224-19=205]
That's why New York has every chance of penetrating the casemate armor belt
and inflicting damage on Fuso
following the rules we discussed in our previous episodes.
But this will happen only if the shell to armor incidence angle
is close to 90 degrees.
The thing is, the shell penetration is compared with not only the armor,
but with the relative armor.
Relative armor is the armor thickness
calculated taking into account the shell to armor incidence angle.
The sharper the angle, the more armor a shell needs to penetrate.
A deviation of 5 to 10 degrees will lead to the following:
both the antitorpedo protection and the casemate armor belt
will become thicker by a few millimeters,
but it will be sufficient enough
to prevent the 205 millimeters of the shell penetration
from piercing the 203-millimeter armor and Fuso will remain undamaged.
However, an AP shell has another important parameter—normalization.
It's a small increase (but as we saw, even a few degrees matter)
of the angle of incidence towards the perpendicular of the plate's surface,
and, therefore, a decrease of the relative armor.
Normalization of the 356-millimeter caliber is 6 degrees.
That's why our small deviation by 5-10 degrees will be compensated
and the casemate armor belt will be penetrated,
but the citadel armor deck will withstand the hit,
so Fuso will lose only 3,300 HP.
Now, let's put New York 5 kilometers away and fire a shell.
The shell penetration is 337 millimeters,
and the angle of incidence is close to the perpendicular of the plate's surface,
so there is enough armor penetration for three layers
of the 321-millimeter armor protecting Fuso's citadel from damage.
However, as you already know,
a shell passes through all the checks for each armor layer:
starting with the 14.3 caliber rule and ending with the normalization.
The shell penetrates the first two layers,
hits the citadel armor deck at a very sharp angle, and bounces off.
Then, it explodes in the casemate and deals 3,300 damage again.
But if a shell hits Fuso's side a little close to the forward end and lower,
it will have to penetrate 19 millimeters of antitorpedo protection,
229 millimeters of the casemate armor belt,
and 76 millimeters of the citadel armor deck slopes located at different angles.
In total, there are 324 millimeters,
which a shell from New York will penetrate
and inflict the full damage on the prized citadel.
And what will happen if a shell hits Fuso's fore end?
The armor thickness in the most protected spot is 102 millimeters.
The armor penetration of New York's primary armament
from 15 kilometers away will be enough for a shell
to over-penetrate through Fuso and fall into the water.
But engineers made sure that the AP shells
would deliver their harmful payload to the hull, through the armor.
The AP shells have a special fuse installed inside;
it activates after a shell penetrates armor of a specific thickness.
Activation of a fuse is delayed,
so a shell has some time to reach "deeper" into a ship after a hit.
If the thickness of the penetrated armor
is greater or equals 1/6th of the shell caliber,
the fuse activates, and the shell detonates,
inflicting damage to whichever part the shell ended up in.
In our example, New York's shells need to penetrate
at least 59 millimeters of armor to be activated.
It doesn't matter how many layers of thinner armor it's going to penetrate,
the fuse won't activate by any means.
Therefore, after the shell penetrates Fuso's 102-mm fore end armor belt,
the shell will successfully detonate inside.
However, if the shell hits the 25-mm fore end casing above the armor belt,
the fuse won't activate, and the shell will fly through the ship,
inflicting only 10% of the damage with the over-penetration.
We can get the same result when a shell hits a superstructure
or when a shell activates inside of the ship's end
and manages to over-penetrate the ship before detonating.
Another interesting showcase is when a shell falls into the water.
After that, it activates automatically.
Then, the fate of the shell depends on the angle of incidence—
the velocity and, therefore,
armor penetration of a shell are significantly reduced in water,
and the trajectory slightly changes.
However, the shell has a chance to reach the underwater parts of a ship,
penetrate them, and detonate inside of a ship.
Such hits are extremely dangerous for destroyers—
it's easy to penetrate a destroyer's side even underwater,
plus, the fuse has been activated by hitting the water.
As you can see, multi-layered armor is a unique feature of the ships' armor
that has its advantages and disadvantages.
But then, a question arises:
what should I do if my shells don't penetrate an enemy ship?
You'll find the answer to that question in our next episode of How it Works,
which will be dedicated to HE shells.
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