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What is a citadel and why should I care? (Lert)


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(Note: Copy and courtesy of a post by Lert)

What is a citadel?

In short, a citadel is where a ship keeps its vital organs. Machinery spaces, turret barbettes, etc.

20.jpeg    Citadel on Italian BB Roma

The citadel on my Roma. As you can see, it stretches from the #1 barbette all through the length of the ship to just aft of the #3 barbette. This is where all the vital machinery is kept that keeps the ship functioning. Boilers, turbines, barbettes, etc.

You keep using the word barbette. What's a barbette?

21.jpeg     Barbette location example

Roma's turret barbettes. Barbettes are round, armored structures that house a turret's ammo hoists, machinery, etc.

So, barbettes are part of the citadel?

In general, no. The citadel extends to include the barbettes lengthwise, but the barbettes project above the citadel and are not part of the citadel. You can get hit in a barbette without getting citadeled.

What about magazines? Is any magazine hit automatically a citadel hit, or vice versa?

That varies per ship. Many ships keep their magazines inside their citadel, especially bigger ships at higher tiers, but a great many ships have their magazines outside the citadel and thus can be detonated without getting hit in the citadel.

Also, magazines are much smaller than citadels, so even if a ship keeps its magazines in its citadel, hitting the citadel doesn't automatically mean a magazine hit.

In short, magazines and citadels are two related but separate entities.

Why should I care about the citadel?

A shell that goes in one side of the ship and flies out the other without detonating does 10% damage. This is an overpen.

A shell that goes in one side of the ship and then detonates does 33% damage. This is a normal pen.

A shell that goes in one side of the ship, then into the citadel and detonates, does 100% damage. This is a citadel hit.

In short, a citadel hit does three times the damage of a normal penetrating hit and ten times the damage of an overpen. That's why you should care about citadels. It takes a third of the hits - thus time - to kill a ship through citadel hits than it does through normal penetrations.

So, hitting a citadel with AP always does increased damage?

Only if your AP shell detonates inside the citadel. Yes, you can overpen a citadel and do reduced damage if your shell is fast enough and your target flimsy enough. For example, Roma has a notoriously fast AP shell with normal fuse timing. Hitting a flimsy cruiser like an Omaha in the citadel at the close-ish range will just mean your shell goes in one end and Yolo's out the other before detonating, causing only 10% overpen damage.

Okay, so hit the citadel for massive damage. Got it. So, the citadel is the weak spot?

Not really. A ship's citadel tends to be the most heavily protected part of the ship. Take my Grosser Kurfuerst, for example:

22.jpeg   German BB Grosser Kurfuerst with Turtleback

In order to get to the citadel, you have to go through a 380mm belt slanted outwards, a heavily slanted 150mm turtleback, and a 45mm bulkhead. That's three layers of armor, thus three ricochet/auto bounce checks. We'll get back to why that matters after ...

Wait, what? Slow down a bit. Turtleback? What's that?

A turtleback is a feature of some ships in this game. Most notably, German battleships and, to a lesser extent, cruisers, but more nations experimented with several similar designs.

In the screenshot of my Grosser Kurfuerst, see where I've indicated the 150mm armor plate? It's sloped back heavily to the point where a shell that manages to get through the 380mm armor belt hits this additional 150mm plate at such an angle that it's very likely just to bounce harmlessly off, never hitting the citadel directly. This makes ships like the Grosser Kurfuerst very resilient and nearly impossible to citadel. It can be done, but usually only from very long range, where the shell goes in through the much thinner upper belt and hits the turtleback at a much steeper angle, negating the auto bounce effect.

Of course, any shell that goes through the armor belt but bounces off the turtleback still does normal pen damage, but this is only 33% of the listed damage number, a far cry from a citadel hit, which does 100% of the listed damage.

Autobounce? Ricochet?

Yes. Any AP shell has two ricochet angles: A lower value, where you start getting a % chance for an automatic bounce, and an upper value, where the chance becomes 100%. To make things even more confusing, different AP shells have different values.

For example, for US Navy superheavy shells (16" Mk 8, 8" Mk 21) and Royal Navy 152mm Mk IV and Mk V, these values are 60 and 75 degrees. That means that by hitting an armor plate at 59 degrees, you'll never get a ricochet; between 60 and 80 degrees, you'll get an ever-increasing chance to ricochet, and when impacting at an angle above 75 degrees, you'll always ricochet.

For most other AP (like, for instance, German battleships or French cruisers), these values are 45 and 60 degrees, and for lower-tier Royal Navy cruisers up to and including Emerald, it's actually 65 and 80 degrees.

You can see every shell in the game and check their auto-bounce angles here.

Note that you can still bounce a shell if it hits at an angle less than the minimum ricochet angle. When this happens, it's because your shell didn't have enough penetration to go through that armor at that angle/range, not because of ricochet mechanics.

One important note to remember is the overmatch mechanic. A shell will ignore an armor plate if the shell's caliber is 14.3x or higher than the armor plate's thickness. So, for example, a 16" AP shell will ignore a 25mm plate of armor, no matter the angle.

So how does this apply to turtlebacks and citadels?

Remember how the 150mm turtleback is so steeply angled? Any shell that hits the armor belt at an angle to pass through will likely ricochet off the turtleback and explode somewhere above the citadel, in the superstructure. This makes turtlebacks such an effective means to protect the citadel.

Now, back to what you said earlier about three layers of armor ... ?

Yes. Kurfuerst's citadel is hidden behind three layers of armor, each with a different angle. Each of these three layers of armor is thick enough so that any shell that exists in this game will not overmatch them and thus aren't ignored. And every layer of armor that an AP shell hits causes a ricochet calculation - except where overmatch happens, which we just established is not in play here. And with the wildly different angles, the plates sit at, there's a very good chance that any AP shell that hits that area will fail at least one of the ricochet checks and not go through into the citadel.

Can you only citadel ships with AP?

No. You can citadel ships with HE, but it's not as easy as with AP. Behold my De Grasse:

23.jpeg    French Cruiser DeGrasse

You can see that a part of the citadel, the yellow 'check,' is flush with the side of the ship. It's only 100mm thick, and hitting it with sufficiently large HE is enough to cause a citadel hit. In order to do this, you need to use stupidly large HE, though, as it needs to have sufficient penetration to go through 100mm of armor. Nelson's 16" HE can do it, for example.

Nominally, HE shells penetrate armor plates up to 1/6 of their caliber rounded down, so a 100mm HE shell can penetrate 16mm of armor. Adding IFHE increases that by 30%, allowing a 100mm HE shell to penetrate up to 21mm. Of course, this being a WG product, and they don't like making things simple, there are exceptions. In this case, British battleship HE, as well as some German HE, have a base penetration of 1/4 instead of 1/6, which can be further enhanced by using IFHE.

So citadels are very difficult to hit?

Some of them, like those on German battleships, yes. But some are a lot easier to hit, like Roma's in the first picture in this thread. Note how Roma's citadel extends a bit above the waterline and doesn't have any tricks like turtlebacks protecting it. It's just a 375m armor belt and a 40mm bulkhead at the same angle.

Knowing which citadels are easy to hit and which aren't is a big part of being a good player. This is, unfortunately, not something I can easily list in a simple, rule-of-thumb thread like this, but something you'll have to learn by experience.

When should I try going for citadel hits, and where should I aim? And which ships should I use?

Use ships with powerful AP and aim center mass, waterline. Shoot at targets that are roughly broadside onto you, and pick targets carefully. The basic rule of thumb is that battleships citadel broadside cruisers and battleships from any range. Cruisers can citadel cruisers from medium and battleships from close range, and destroyers can citadel light cruisers from close range.

However, keep in mind that some ships have very effective turtlebacks (German battleships, for example) or submerged citadels (most of the British battleships except for Nelson), so you're not going to hit their citadels easily, if at all. Destroyers can't be citadeled by anything at any range. They do have a machinery box, but this isn't treated as a hitbox by the game. This is on purpose - back in Alpha, destroyers could be citadeled, and they were just unfun to play, getting deleted by anything that breathed at them moderately harshly.

Is there any way to protect my own citadel from getting hit?

There is no way to 100% protect your own citadel, but you can do a lot to mitigate it. You can keep your angles in mind and present the most layers of armor at the weirdest angles. Remember that every single layer of armor triggers a ricochet calculation, so present more layers at steeper angles, and you should minimize the risk of getting citadeled - as long as they're not using guns that flat-out ignore your armor because of overmatch.

24.jpeg     Yamato citadel example

Yamato's citadel, or at least the forward part of it. If you go broadside in a Yamato, enemy battleships can just yolo their AP straight through the 410mm side belt straight into the citadel. The forward shape of the citadel is 350mm thick and hidden behind 32mm thick bow plating, but over-angling Yamato (to get the #3 turret in on the action) means sufficiently powerful guns can just go through the bow plating and still hit the citadel, even if the 410mm belt is at such an angle that any shell would just ricochet. Plus, Yamato (and Musashi) have guns of 460mm caliber. Remember the old overmatch rule? These shells are the only ones in this game large enough just outright to ignore the 32mm bow plating and go straight into the citadel at any angle.

Anyway, I hope this guide was of some use to some people. If you ever see me on the red team, please conveniently forget everything you've learned here. Thanks.

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Great work, though it should be noted that some of the precise details are no longer accurate due to the continuous inflow of new contents and balance changes as well as some simplification.

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@Project45_Opytnynoted!  There will be general edits/fixes to several articles as we move forward.  Right now the main goal is to preserve suggested articles/guides from the old forums.

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