Armor and Compartmentalization

Armor

Armor in World of Warships is not just a uniform barrier to be pierced (like in World of Tanks), but rather a kind of multi-layered “cake” that covers a number of construction elements and mechanisms, each having specific armoring.

A projectile that enters the ship can encounter up to four or five layers of armor and may stop or ricochet at each layer. In this regard the developers attempted to adhere to historical realism and simulate all significant layers of armor. The armor tends to be very heavy: on a typical battleship it takes up around 40% of the total displacement of the vessel. Therefore, some later battleship designers tried to save some of that weight by placing heavy armor only around the vital parts of the ship: the ammunition and propellant magazines, the propulsion plant, the fire-control, command and communications sections. Most of the other compartments are almost completely unarmored. This approach of providing either total or negligible protection is referred to as "all or nothing". In effect, the scheme accepts vulnerability to medium-caliber and high-explosive shells striking the unarmored sections of the hull, in order to improve resistance against the heaviest armor-piercing shells, while at the same time being able to carry a powerful armament and retain useful speed and endurance.

IJN Yamato magazine explosion

The ship's vital parts are protected by a citadel, which can be visualized as an open-bottomed (closed top) rectangular armored raft with sloped sides sitting within the hull of the ship. Although it was desirable for the citadel to be as small as possible, the space enclosed was an important source of reserve buoyancy, and helped prevent the ship from foundering when other compartments had flooded. In game, taking the citadel's HP to zero would effectively destroy the ship, even if none of the other compartments were affected.

Battleship cross-section

From the citadel box, shafts known as barbettes lead upwards to the ship's main gun turrets and conning tower. The ship's magazines are located in or around the turret barbettes, and contain the main caliber shells, as well as the gunpowder charges. Penetrating the citadel armor around the magazine often results in a spectacular one-shot kill.

How can a player know where these important compartments are when he or she fires into the side of an unfamiliar ship? Short of looking up ship's blueprint, an educated guess will have to suffice. The citadel is normally located in the middle of the ship, and is roughly half the ship's length. As a rule-of-thumb, when you have a clear shot at the side of the ship, aim in the middle of the ship (just below the smokestacks), and close to the waterline. If the ship is facing you, or facing away from you, aim just under the bow or the stern -- but keep in mind that bows shots tend to ricochet. The magazines are normally located just under the main caliber turrets.

In addition to belt armor, which protects battleships from direct fire, they also have deck armor that protects them from plunging fire -- shells at extreme engagement ranges tend to hit the top of the ship. However, due to to a large area that would have to be protected, battleships' deck armor is much thinner than the belt armor. As such, shells fired to strike the deck may be able to defeat the armor while those same shells may be incapable of penetrating the side armor of the target vessel.

Compartmentalization

See also: Damage Saturation for an in-depth explanation.

A ship has to be both a military base and a combat vehicle, since it is designed for long autonomous operations. Therefore a significant portion of the ship's interior space is needed for the every-day activities, but has no direct effect on ship's fighting capacity in the critical moments of the battle. A shell that destroyed the ship's laundry room or the galley in an artillery duel would have much less of an immediate effect on combat capability than a shell that hit the magazine or the engine compartment.

That is why, unlike the vehicles of World of Tanks, ships in World of Warships are divided into multiple compartments, each with a different value of hit points (HP). Damage is "dealt" to a compartment by subtracting a certain amount of hitpoints. The compartments are as follows: bow end, aft end, citadel, casemate (center part minus the citadel), and the superstructure. In addition, each ship's model in the game is assigned another, virtual compartment called "entire hull". The total hit points value for all these compartments combined is slightly more than the ship's nominal hit point pool. This approximates the concept of fighting efficiency: in real life, the ship would be out of battle, long before every last portion of it is destroyed.

Each compartment (except the citadel) has two thresholds, where after each one is reached the damage it receives is reduced. The threshold levels for each compartment of each ship varies.

In the initial state, the ship will receive damage normally (x0.33 for shell penetration). The compartment starts off clean and gets darker as it takes more damage.

After the first threshold is reached, the damage received is halved (x0.165 dmg for shell penetration). At this stage, the compartment of the ship is visually blackened.

Finally, once the second threshold is reached the compartment stops receiving damage, an effect known as damage saturation. There is no visual difference to the first threshold, you'll only notice that your shells stop doing damage to the compartment.

Regardless of the state of the compartment, over-penetration will always deal x0.1 dmg and citadel hits will always deal x1.0 damage, even after the compartment's HP pool is completely depleted.

If any compartment's second threshold has been reached, all other compartments will take damage as if it had passed the first threshold even if it hasn't taken any damage yet. Damage from fire, flooding, ramming, over-penetration and citadel hits will not reduce any compartment's HP pool (but they will still reduce the ship's total HP as normal). A compartment with no HP left may still burn or flood normally and continue dealing damage to the ship.



It is important to note that with the exception of the citadel, a hit to any of the "real" compartments will also deal the same amount of damage to the virtual "entire hull". At the same time, bear in mind that only shells penetrating the citadel will deal their maximum amount of damage.

Modules

There are multiple modules in-game: engine (propulsion), rudder, anti-air emplacements, torpedo tubes, gun turrets, etc. The modules have three states: functioning, damaged, and destroyed. A damaged module loses function until it is repaired, a destroyed module cannot regain function. Some modules can only be damaged but not destroyed (e.g. propeller), other modules can only be destroyed but not damaged (e.g. AA emplacements).

Each module has a certain amount of HP. Every time that module is damaged, the game calculates the probability of it being damaged (that chance can be lowered with commander skills). The probability of a critical hit that leads to damage increases for lower module HP values. Once the module reaches zero HP, it is destroyed.

Shell Types

Typical HE and AP shells

World of Warships currently has two types of shells:

High-explosive (HE)

Armor-piercing (AP)

The ballistic models for AP and HE shells are identical; however, some ships have different muzzle velocities between their HE and AP shells. Shell's in-game tracer may not coincide with the actual trajectory, in order to better visualize the shooting process.

High-Explosive (HE)

These shells have an instant fuse and burst immediately upon hitting a target. In addition to any direct damage, HE shells are good for knocking out modules, particularly deck mounted ones like AA emplacements, as well as starting fires, which can deal a large amount of damage over time if not extinguished. Like AP shells, HE does zero damage on shatters, 1/3 damage on normal penetrations, and max damage on citadel penetrations.

Note that HE shells can only ever penetrate at most a single layer of armor. This can cause them to score a regular penetrating hit rather than a citadel hit if they strike another layer of armor first, no matter how thin the two layers are. This is an advantage of some spaced or turtleback armor schemes. In some cases, when they hit an "empty" section of the ship such as a torpedo belt, they can even fail to do any direct damage at all.

HE penetration

Unlike AP shells, the penetration of HE shells does not depend on the impact angle or velocity---rather, each HE shell has a fixed penetration value which is compared to the raw thickness of the armor. This is computed using the following steps:

Start with the shell diameter in mm. Multiply by a factor: 1/4 for British battleship primary armament (except Warspite), German battleships (Primaries, 150mm and 128mm secondaries at all tiers and 105mm secondaries of Friedrich Der Große ), German cruisers (tiers IV-X primary armament and 150mm secondaries), and Japanese 100mm guns (Primaries and secondaries).

), German cruisers (tiers IV-X primary armament and 150mm secondaries), and Japanese 100mm guns (Primaries and secondaries). 1/6 for all other shells. Round to the nearest integer, with X.5 usually rounding up, though even this is not consistent. This is the shatter threshold, the minimum armor thickness in mm needed to shatter the shell. If the commander has the Inertia Fuse for HE Shells skill, multiply the original (stock) shatter threshold by 1.25. Do not round again.

See this article for some key thresholds.

In summary:

Armor needed to shatter HE shell Ships Without IFHE With IFHE Default round(shell diameter / 6) round(shell diameter / 6) * 1.3 Bayard round(shell diameter / 5) round(shell diameter / 5) * 1.3 British battleships,

German cruisers,

German battleships,

Japanese 100mm guns

round(shell diameter / 4)

round(shell diameter / 4) * 1.3

If the thickness of the armor is equal to or greater than the shatter threshold, the shell shatters. On the other hand, if the shatter threshold is strictly greater than the thickness of the armor, it penetrates.

Example: Cleveland has a shell diameter of 152 mm. Dividing 152 by 6 gives an HE penetration value of 25.33 mm, which is rounded to 25 mm. Thus, any armor plate of 25 mm or thicker will shatter her shells, while armor of 24 mm or thinner will be penetrated. With IFHE, that value increases to 25 mm * 1.3 = 32.5 mm (not rounded). Thus, with IFHE it would take at least a 33 mm plate to shatter her shells, while armor of 32 mm or thinner would be penetrated.

The reverse calculation is as follows:

Maximum HE shell diameter shattered by armor Ships Without IFHE With IFHE Default (armor + 0.5) * 6 (floor(armor / 1.3) + 0.5) * 6 Bayard (armor + 0.5) * 5 (floor(armor / 1.3) + 0.5) * 5 British battleships,

German cruisers,

German battleships,

Japanese 100mm guns

(armor + 0.5) * 4

(floor(armor / 1.3) + 0.5) * 4

Example: Shchors has 75 mm of citadel armor. Therefore she can shatter normal HE shells of up to (75 + 0.5) * 6 = 453 mm diameter, but she would be citadelled by shells of 454 mm or larger. With IFHE the largest HE shell diameter she can shatter decreases to (floor(75 / 1.3) + 0.5) * 6 = 345 mm, with HE shells of 346 mm being able to citadel her. British battleships, German cruisers, and German battleships without IFHE can citadel Shchors with shells exceeding 302 mm. With the addition of IFHE, such ships can citadel her with shells exceeding 230 mm diameter.

Armor-Piercing

Unlike HE, the AP shell does damage only if it penetrates the armor. The fuse of the AP shell is initiated after it passes through armor, and historically the fuse times were calculated in a way that would allow the shell to explode after traveling about ten or so meters after passing through the armor; that way the shell exploded around the middle of the battleship. That means that when AP shells are fired at lightly armored and relatively small target, they might over-penetrate -- explode once they passed through the entire ship, or not even explode, if the shell doesn't encounter enough armor to detonate. Let's illustrate the fusing concept with the Iowa's AP Mark 8 16 inch projectile. Its Mark 21 Base Detonating Fuse (BDF) had a delay of 0.033 seconds. Fuse activation requires a resistance equal to 1.5 inches (3.8 cm) of armor at 0 degrees obliquity or 0.375 inches (1 cm) at 65 degrees obliquity. The muzzle velocity for a new gun and a full charge is 762 meters per second. Therefore, if the shell were to immediately hit an armor plate 1.5 inches thick after exiting the barrel, it would explode 762*0.033 = 25 meters after passing through that armor plate. Most AP shells in game have a fusing time of 0.033 seconds, but there are shells with as much as 0.1 second fusing time. As of patch 0.3.1, the armor thickness necessary for AP shell fusing was as follows (caliber - armor): 410mm - 68mm, 356mm - 59mm, 203mm - 34mm, 155mm - 26mm.

Non-penetrations (bounce/ricochet) will always deal 0 damage, regardless of AP or HE (the latter cannot ricochet). However, HE shells still has a chance to start fires or break modules with its splash damage). Most ships use the following angles for AP ricochets:

0-30 degrees -> auto ricochet

30-45 degrees -> chance to ricochet

45-90 degrees -> ricochet doesn't occur

As of 0.7.6, no ships have "worse" angles.

The following ships have improved angles:

*Due to this setting, Tachibana's AP will never ricochet. This is not a bug.

Penetrations deal x0.33 of the shell's listed damage. Whether AP or HE, it must penetrate the armor and detonate inside the ship. Over-penetrations deal x0.10 of the shell's listed damage. Over-penetration is when a shell penetrates the ship through-and-through, before it has a chance to detonate inside the ship. Theoretically HE will never over-penetrate due to its low detonator threshold and shorter fuse. Citadel hits will always deal x1.0 of the shell's listed damage (though citadel over-penetration is still possible, and will only deal x0.10 damage). It is impossible to get a citadel hit on a destroyer, as they no longer have them per se (it was removed in 0.2.4/0.3.0). Prior to 0.4.1, penetrations on a destroyer's midsection will deal x0.5 of the shell's listed damage (in lieu of the absence of citadels), however this is no longer the case and penetrations to it will deal the standard x0.33 of the shell's listed damage.

Special limit:

Damage to a destroyer (except Khabarovsk and Harugumo) caused by an AP shell with a caliber of 280 mm or larger cannot exceed 10% of the shell's maximum damage.[1]

Properly angling the ship matters a great deal when the enemy is shooting AP shells: when an AP shell encounters armor at an angle, it has to pass a greater amount of armor for penetration. Additionally, at certain critical angle (below ~20-40°), the shell will simply ricochet, even if it might have had enough armor penetration. A shell may still cause damage after the ricochet, but only to the same ship.

If the armor thickness is less than 1/14.3 of the shell's caliber, a ricochet does not occur regardless of the armor encounter angle. This phenomenon is called overmatching. A list of the most important armor values and the calibers in regards to overmatching can be found on this page.

There are certain engagement ranges when AP shells will encounter both the belt and the deck armor at fairly large angles, and will have a high probability of either non-penetration or ricochets. The distance at which both plunging fire and direct enemy fire is less effective is called the immunity zone (IZ). Despite the absolutist nature of its name, the immunity zone concept does not imply any sort of invulnerability. A ship fighting within its IZ will still probably suffer when hit, but it is theoretically proof against singularly catastrophic hits to the citadel. (Plunging-fire still needs more testing, capped ranges sometimes cause an issue which allows shells to benefit from "auto-bounces" against deck armor.)

Underwater shell trajectory

AP shells can penetrate ship's armor even below the waterline, after traveling through water. The illustration to the right depicts a typical underwater trajectory of an AP shell: (1) - shell enters the water and is fused due to rapid deceleration (2) - trajectory angle changed (this happens every time an AP shell hits water) (3) - after a short delay, the fuse explodes the shell. The image also demonstrates two outcomes of an underwater hit: armor penetration, and a ricochet. As of 0.4.1 the underwater hits do not cause flooding.

Armor-Piercing Internal Ricochets

An AP shell that ricochets after penetrating armor will cause another instance of penetration damage in the section where the ricochet occurs. Additional ricochets will cause additional instances of penetration damage until the shell exits the ship or explodes from fuse activation.

This extra source of damage is most commonly encountered when shooting at "turtleback" armor schemes (common on all German battleships and other nations' dreadnoughts). Plunging fire that is insufficient to penetrate interior decks may also ricochet, causing one or more extra instances of damage.

Secondary Guns

As a general rule, secondary guns fire HE. Ones that fire AP did exist, but have been replaced by HE in patch 0.7.11.

Secondaries aim at enemy ship's mid-ship waterline. At comparatively long ranges, dispersion causes shells to scatter onto other parts of the enemy ship. However at close ranges, secondaries will likely hit the main belt of the enemy ship. In this case, unless the enemy ship has no belt armor, HE secondaries would usually shatter.

Choosing Between AP and HE Shells

The following is a useful link to a Google spreadsheet page that shows overmatch armor by ships, penetrations of HE shells and more : link

Some general guidelines for each of the three ship classes:

As a Battleship

Shooting other battleships with AP is most effective with direct fire at point-blank and medium ranges, roughly up to ~10-12 kilometers. The enemy battleship shouldn't be at too great of an angle; ideally, it should be perpendicular to your line of fire. You might also get some citadel hits with plunging fire at maximum fire ranges. If you aren't positive that you have a good chance of penetrating the citadel, HE shells are a better choice.

AP shells should be used against well-armored cruisers and carriers as well, when you are certain that a volley at the waterline will penetrate the citadel. Since their armor thickness will be nowhere near that of a battleship, angling will affect your AP shells to a lesser degree. It might be a good idea to light a carrier on fire first, though, to prevent it from launching aircraft

Against lightly-armored cruisers and carriers, you should be using HE shells -- they have enough armor penetration to damage citadels. However, some carriers have enough armor to resist HE, and AP should be shot at them. It must also be noted that an AP shell can deal much more damage against a citadel. You should also use HE against destroyers -- AP shells will almost always over-penetrate; and HE shells will knock out multiple modules on a DD, giving you a high chance of disabling it even if it doesn't kill.

One last thing: it's better to use the shell of the wrong type (e.g. AP against a destroyer that suddenly materialized near your ship) than to start a long half-minute reload. Sub-optimal damage is better than no damage at all.

Cruisers

Against battleships your best bet is HE shells. Consistent HE hits and nonstop fires are a bane of many battleship drivers' existence. However, don't try to fight a battleship single-handedly; a skilled BB driver can dispatch you in a few well-aimed AP salvos. At point-blank ranges and favorable angles you can also try to penetrate the battleship's citadel with AP shells, though it's generally not a good idea to be that close to a battleship in the first place.

Against other cruisers and carriers use AP shells at close and medium ranges, when you can reliably hit the citadel: a well-aimed salvo remove as much as half of the other cruiser's HP. If the cruiser is far away, or is angling too much, use HE; HE should also be used against the destroyers in practically all situations.

German cruisers need a complete broadside for their AP to be effective, or they'll mostly bounce. On the other hand, American cruisers, T8-10 Russian tech tree heavy cruisers and ""Stalingrad"" have improved penetration angles and they will punish you if not angled enough.

Destroyers

When driving most destroyers, your main weapons should be your torpedoes (especially so if you're driving an IJN DD). However, HE shells can still be very useful when fighting other destroyers, or providing additional fire against enemy capital ships -- in the latter case, your shells won't be doing much damage, but you can make up for that with the sheer number of shells, and fires.

AP shells can sometimes be used against lightly armored enemy cruisers and carriers, since you have just enough armor penetration to defeat their citadel armor, and can also sometimes be used against other Destroyers because of their higher damage (although they will not destroy modules like HE shells do). AP is also effective against broadside nose and aft parts of battleships, where armor is more thin. You can farm surprisingly much damage if you hit these parts with AP when they are not angled.

Shell Dispersion

Illustration of artillery dispersion

However perfectly a naval gun on a stationary ship may be laying, successive rounds will not impact on a single point but will fall in a pattern scattered both in deflection and in range. This phenomenon is called dispersion and, irrespective of human and constant error, it is caused by multiple inherent factors: minor variations in the weight of the projectile, differences in the rate of ignition of the propellant, variations in the temperature of the bore from round to round, physical limitations of precision in setting values of deflection and quadrant elevation on the respective scales, minor variations in wind, air density or air pressure, and so on.

Dispersion values for main caliber guns are displayed in port

Observing the position of the surface bursts around our point of aim, we find that they fall into a roughly elliptical area in relation to the line of fire. An ellipse constructed around the dispersion area is called the dispersion ellipse. Every time a player orders his main caliber guns to fire, the game engine constructs a 2-D ellipse around the point of aim, and does so independently for each salvo fired. A double-click will fire all guns in one salvo with one dispersion ellipse, sequential fire will construct dispersion ellipse for each turret salvo separately. This ellipse has a certain length and width values, which are dependent on the characteristics of the gun. The dispersion value displayed in port is the horizontal length of the dispersion ellipse at the maximum fire range, i.e. a value that describes the lateral distribution of the shells relative to the player's ship.

Shell impacts within the dispersion ellipse are not uniformly distributed over the surface, but lie more thickly towards the center of aim. The intensity with which the shells fall in different points of the area of dispersion, can be described by a Gaussian (normal) distribution. The in-port value describes dispersion in terms of one probable error, i.e. it gives a value where 50% of the fired shells will land around the point of aim. This has been confirmed by experiments conducted by the players. Port dispersion value (red bar in the graph below) is the standard deviation (green bar) of shell hits across the horizontal axis of the dispersion ellipse:

If the shooting distance is below the maximum range, the horizontal dispersion value decreases accordingly. Horizontal dispersion values at distances other than maximum firing range, as well as the vertical dispersion values have not been made public by WarGaming. However, based on the user collected data we know lines of tech tree ships are tied to specific formulas to determine horizontal dispersion. The graph below shows the dispersion curves for each ship in the game, followed by it's table and the formulas used.



