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Armor Penetration

Armor Penetration

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Armor and Compartmentalization

Armor

Armor in World of Warships is not just a uniform barrier to be pierced (like in WoT), 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 be stopped 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, 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

Approximate location of essential modules

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 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

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 effect on combat capability than a shell that hit the magazine or the engine compartment.

File:FiveParts.jpeg

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). Roughly, the compartments are as follows: bow, stern, citadel, casemate (center part minus the citadel), and the superstructure. The total value of HP for all the compartments is roughly twice the ship's total hit point value ( fighting efficiency): in real life, the ship would be out of battle long before every last portion of it is destroyed.

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

  • In the initial state, the ship will receive damage normally (x0.33 for shell penetration). The section 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 section of the ship is visually blackened.
  • Finally, once the second threshold is reached the section stops receiving damage. There is no visual difference to the first threshold, you'll only notice that your shells stop doing damage to the section.
  • Regardless of the state of the section, over-penetration will always deal x0.1 dmg and citadel hits will always deal x1.0 damage, even after the section's HP pool is completely depleted.
  • If the midsection's second threshold has been reached, all other sections will take damage as if it had passed the first threshold even if it hasn't taken any damage yet. Damage from fire, flooding, over-penetration and citadel hits will not reduce any section's HP pool (but they will still reduce the ship's total HP as normal). A section with no HP left may still burn or flood normally and continue dealing damage to the ship.


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 1/6 of the shell's diameter for most ships, but 1/4 for British battleships, German cruisers, and German battleships. This can be increased by 30% with the Inertia Fuze for HE Shells commander skill. The resulting value is then rounded to the nearest mm. If the armor is greater or equal to this value the shell shatters; if the armor is strictly less than this value the shell penetrates. These are summarized in the following tables:

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

round(diameter / 4 )

round(diameter * 1.3 / 4)

Example: Cleveland has a shell diameter of 152 mm. This gives her a HE penetration of 25.33 mm, which is rounded to 25 mm. Thus, any armor plate of 25 mm or greater will shatter her shells, while armor of 24 mm or lower will be penetrated. With IFHE, the HE penetration increases to 32.93, which is rounded to 33 mm. Thus, with IFHE it would take at least a 33 mm plate to shatter her shells, while armor of 32 mm or lower would be penetrated.

HE shell diameter needed to penetrate armor
Ships Without IFHE With IFHE
Default (armor + 0.5) * 6 (armor + 0.5) * 6 / 1.3
British battleships
German cruisers
German battleships

(armor + 0.5) * 4

(armor + 0.5) * 4 / 1.3

Example: Shchors has 75 mm of citadel armor. Therefore it would take at least (75 + 0.5) * 6 = 453 mm shell diameter to citadel her with HE. With IFHE this decreases to (75 + 0.5) * 6 / 1.3 = 348.46 mm, or 349 mm since all shell diameters are integers. British battleships, German cruisers, and German battleships without IFHE can citadel Shchors with 302 mm shells or greater. With the addition of IFHE, such ships can citadel her with shells of at least 233 mm diameter.

Armor-Piercing

Unlike HE, the AP shell does damage only if it penetrates the armor. The fuze of the AP shell is initiated after it passes through armor, and historically the fuze 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 activate the fuze. Let's illustrate the fuzing concept with the Iowa's AP Mark 8 16 inch projectile. Its Mark 21 Base Detonating Fuze (BDF) had a delay of 0.033 seconds. Fuze 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 fuzing time of 0.033 seconds, but there are shells with as much as 0.1 second fuzing time. As of patch 0.3.1, the armor thickness necessary for AP shell fuzing 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). The angles for AP ricochets are as follows:

  • 0-30 degrees -> auto ricochet (0-22.5 for USN 8" shells)
  • 30-45 degrees -> chance to ricochet (22.5-30 for USN 8" shells)
  • 45-90 degrees -> ricochet doesn't occur (30-90 for USN 8" shells)

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 fuze. 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.

Frame_3b_V04_eng_small.gif

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 ad 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 shell's caliber, a ricochet does not occur regardless of armor encounter angle.

Frame_1a_V04_eng_small.gif

Frame_1b_V04_eng_small.gif

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 need more testing, the issue with the capped ranges causing the shells were benefit from it being "auto-bounce" against deck armor)

Immunity_zone.jpeg

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 fuzed due to rapid deceleration (2) - trajectory angle changed (this happens every time an AP shell hits water) (3) - after a short delay, the fuze 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.