Armor Penetration

   

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 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

The ship's vital parts are protected by a citadel, which can be visualized as an heavy armored box within the ship which contains the most vital machinery and vulnerable ammunition stores. 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, successfully causing damage to the citadel causes shells to inflict their maximum damage and such damage is the most difficult to repair.

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 and detonating the stored ammunition 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? The citadel is rarely any further forward on a ship than her fore-most turret, and likewise rarely any closer to the stern than the aft-most turrets. Most ships citadels have their roof a short way above the waterline and on some the added plating on the side of the ship distinguishes the ships citadel belt (the side armor that protects the citadel) from the casemate belt (with the casemate being the rooms ontop of the citadel that form the deck that the superstructure sits upon). The armor scheme of ships is viewable ingame by expanding the Armor Layout section of the ships parameters found on the right hand side when viewing any ship in port.

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 and aerial bombs. 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.

Damage Saturation

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.

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. Furthermore, dealing repeated damage to the same part of a ship becomes increasingly inefficient as a ship cannot be sunk by damaging only one compartment of the ship alone (unless that compartment is the citadel). This reduction is called Saturation;

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.

• Initially, the ship will receive damage normally. The section starts off clean and gets darker as it takes more damage.
• Once the first threshold is reached, the damage received is halved. At this stage, the section of the ship is visually blackened. This compartment is now saturated.
• Finally, once the second threshold is reached the section stops receiving damage exceeding 10% of a shells listed 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-penetrations will always deal 10% of listed shell damage and citadel hits will always deal 100% of listed shell damage because the citadel section cannot be fully depleted. Saturation also affects the damage done by torpedoes, but torpedoes will also always deal at least 10% of their maximum damage.
• 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.

For a more in-depth explanation please see the full article; Damage Saturation.

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 based upon the calibre of the shell which is compared to the raw thickness of the armor to determine a successful penetration. The formula for calculating this penetration value depends on a penetration coefficient based on the nation and type of ship.

The default coefficient is 1/6th of the shell's diameter, but 1/4th for most British battleships, certain German cruisers, and certain German battleships. Cruisers from Tier VIII-X with caliber of 150-155mm enjoys 1/5th HE penetration. Additionally, Japanese ships with 100mm main and secondary guns have special penetration value of 30 mm.

If the armor is greater than this HE penetration value the shell shatters; if the armor is less or equal this value the shell penetrates. This penetration value can be increased by 25% with the Inertia Fuze for HE Shells (IFHE) commander skill but at the cost of halving the ships base fire chance.

HE coefficients are summarized in the following table:

HE Penetration Coefficient	Guns/Ships Affected
30mm specific penetration	100mm Type 98 main guns of Akizuki, Kitakaze, Harugumo 100mm Type 98 Secondary guns of various IJN ships such as Zao, Azuma, Kii, Iwami & Shikishima
1/4th penetration	German Battleship Main Guns 150mm+ German Cruiser Main Guns 128mm+ German Destroyer Main Guns 105mm, 128mm & 150mm German Secondaries British Battleship Main Guns (except Warspite, Hood, Collingwood, Renown '44, Incomparable, the Indefatigable—St. Vincent tech tree line) 234mm British Cruiser Main Guns of Cheshire, Drake & Goliath 234mm Secondary guns of Atlântico
1/5th penetration	150-155mm Main Guns of Tier VIII-X Cruisers (Including the 155mm guns of CA Mogami) 150mm main guns of Tromp 152mm main guns of Ragnar
1/6th penetration	All other ships

The formula for calculating the HE penetration value is as follows.

Gun caliber * the penetration coefficient with the result rounded to the nearest mm (.5 rounds up). This resulting value is the armor thickness that a HE shell can penetrate. Instead of multiplying by 1/4 or 1/6, you can instead divide by 4 or 6 as the math is the same. Here are some examples.

127mm Destroyer Example
127mm / 6 = 21.167mm rounded to 21mm which is the highest armor thickness that a 127mm HE shell can penetrate.
A 127mm HE shell will penetrate armor of 21mm thickness or less.

152mm Tier I-VII Light Cruiser Example
152mm / 6 = 25.333mm rounded to 25mm which is the highest armor thickness that a 152mm HE shell from tier I-VII can penetrate.
A 152mm HE shell will penetrate armor of 25mm thickness or less.

152mm Tier VIII-X Light Cruiser Example
152mm / 5 = 30.4mm rounded to 30mm which is the highest armor thickness that a 152mm HE shell from tier VIII-X can penetrate.
A 152mm HE shell will penetrate armor of 30mm thickness or less.

203mm Heavy Cruiser Example
203mm / 6 = 33.833 rounded to 34mm which is the highest armor thickness that a 203mm HE shell can penetrate.
A 203mm HE shell will penetrate armor of 34mm thickness or less.

The formula for calculating the IFHE penetration value is as follows.

If you have a Commander with the IFHE skill, it will add 25% (x1.25) to the HE penetration value of all HE shells on the ship. So while battleship main guns do not benefit from the IFHE skill as a rule (they already have a high HE penetration value), some players will want the IFHE skill for a secondary gun build. The 25% bonus is added to the rounded HE penetration value from the previous formula. The result of the IFHE calculation is always rounded down to find the HE penetration value. Here are some examples.

127mm Destroyer IFHE Example
127mm / 6 = 21.167mm rounded to 21mm. 21mm * 1.25 = 26.25mm rounded down to 26mm.
A 127mm HE shell with the IFHE skill will shatter on 27mm or greater of armor thickness and penetrate armor of 26mm thickness or less.

152mm Tier I-VII Light Cruiser Example
152mm / 6 = 25.333mm rounded to 25mm. 25mm * 1.25 = 31.25mm rounded down to 31mm.
A 152mm HE shell (lower than Tier VIII) with the IFHE skill will shatter on 32mm or greater of armor thickness and penetrate armor of 31mm thickness or less.

203mm Heavy Cruiser IFHE Example
203mm / 6 = 33.833 rounded to 34mm. 34mm * 1.3 = 42.5mm rounded down to 42mm.
A 203mm HE shell with the IFHE skill will shatter on 43mm or greater of armor thickness and penetrate armor of 42mm thickness or less.

HE shell diameter needed to penetrate armor:

• without IFHE: (armor - 0.5) / (penetration_coefficient)
• with IFHE: (round_up(armor / 1.25) - 0.5) / (penetration_coefficient)

Example: Shchors has 75 mm of citadel armor. Therefore it would take at least (75 - 0.5) / (1/6) = 6 * 75 - 3 = 447 mm shell diameter to citadel her with HE. With IFHE this decreases to (round_up(75 / 1.25) - 0.5) / (1/6) = 6 * 60 - 3 = 357 mm. British battleships, German cruisers, and German battleships without IFHE can citadel Shchors with 298 mm shells or greater. With the addition of IFHE, such ships can citadel her with shells of at least 238 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).

Ricochet angles

Bounce or ricochet angles are stated in reference to the perpendicular, as in the illustration below, that is to say they are relative to a ship being parallel being 0°. The standard angles for AP ricochets are:

• 90-60° → auto ricochet (at 90° a ship is completely bow in)
• 60-45° → chance to ricochet
• 45-00° → ricochet doesn't occur (at 0° a ship is completely broadside)

Ricochet is not always possible; see Overmatch below.

If an AP shell strikes a target at an angle that causes it to ricochet no damage is dealt and the attacker receives a ricochet ribbon.

Some ships fires shells that do not conform to standard angles and have "improved" angles, requiring the target to angle even further from the perpendicular to cause the shells to ricochet.

The following table shows the ricochet angles for AP shells:

Ship	Tier	Nation	Ricochet Chance Begins	Ricochet Guaranteed
Destroyers: Tachibana, Tachibana Lima	II		91°*	Never
Cruisers: Weymouth, Caledon, Danae, Emerald	II - V		65°	80°
Cruisers: Leander, Fiji, Edinburgh, Neptune, Minotaur, Edgar, Plymouth, Gibraltar, Tiger '59, Hampshire, Orion '44 Destroyer : Druid	VI - XI		60°	75°
Cruiser: Mysore	VI		60°	75°
Cruiser: Canarias	VI		60°	75°
Cruisers: Pensacola, New Orleans, Baltimore, Buffalo, Des Moines, Annapolis, Alaska, Alaska B, Anchorage, Congress, Indianapolis, Puerto Rico, Rochester, Salem, Wichita Battleships: Illinois	VI - XI		60°	67.5°
Battleships: Hood, Duke of York Cruisers: Defence Destroyers: Jupiter '42, Jutland, Daring	VII, IX - X		60°	67.5°
Destroyer: Vampire II	X		60°	67.5°
Destroyers: Z-31, Elbing, Felix Schultz, Gustav Julius Maerker, ZF-6	VII - X		60°	67.5°
Destroyer: Fenyang, Ship Smasha	VIII		60°	67.5°
Cruisers: Stalingrad, Pyotr Bagration, Bagration	VIII, X		55°	65°
Battleships: Rhode Island Cruisers: Mikoyan, Tallinn, Dmitry Pozharsky, Riga, Tianjin, Petropavlovsk, Sevastopol, Novosibirsk	V, VIII - XI		50°	65°
Cruiser: Cheshire	VIII		45°	65°
All other ships	All	All	45°	60°

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

The following table shows the ricochet angles for SAP shells:

Ship	Tier	Nation	Ricochet Chance Begins	Ricochet Guaranteed
Giuseppe Verdi, Michelangelo and Napoli: 152mm secondary mounts	IX - X		80°	85°
Battleships: All Italian Battleships, except Giulio Cesare, Roma, AL Littorio, and Giuseppe Verdi Cruisers: All Italian Cruisers, except Duca d'Aosta, Duca degli Abruzzi and Napoli Giuseppe Verdi, Michelangelo and Napoli: 90mm secondary mounts Sicilia: 152mm and 127mm secondary mounts	III - XI		70°	80°
Cruiser: San Diego	VIII		70°	80°
Cruiser: Austin Destroyer: Forrest Sherman	X		65°	75°
Ruggiero di Lauria: 135mm secondary mounts Destroyers: All Italian Destroyers, except Leone Cruiser: Nino Bixio	II - X		60°	75°

AP Shell Damage

Penetrations deal 33% of the shell's listed damage (less when there is damage saturation). Whether AP or HE, it must penetrate the armor and detonate inside the ship. Over-penetrations deal 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 100% of the shell's listed damage (though citadel over-penetration is still possible, and will only deal 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).

Special limit:
Damage to a destroyer caused by an AP or SAP shell with a caliber of 280 mm or larger cannot exceed 10% of the shell's maximum damage.

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 shallow angles to the surface the shell will simply ricochet, even if it might otherwise be able to penetrate. A ricocheting shell may still cause damage, but only to the same ship. For heavy shells vs. thin armor, ricochet cannot occur; see Overmatch below.

Overmatch

If the armor thickness is less than 1/14.3 of an AP or SAP shell's caliber, a ricochet does not occur regardless of armor encounter angle. See this table for examples.

Normalization

Shell impact off the perpendicular, whether due to armor angling or angle of flight, affects the flight path of a shell that passes through the armor. This effect is called 'normalization'. The effect is important with multiple armor layers. Each layer changes the shell flight path toward the perpendicular, with the effect that subsequent layers are easier to penetrate because the angle of impact is closer to the perpendicular, i.e. they 'appear' thinner.

Normalization is modeled by shell caliber.

Caliber	Angle of Deflection
Battleship (283mm+)	6º
Heavy Cruiser (203mm+)	7º
Light Cruiser (140mm+)	8.5º
Destroyer (less than 140mm)	10º

Water (Liquid Armor)

Seawater is really good armor. However, shells that impact the sea in close proximity to a ship can still have significant effects.

• Fuse timers arm immediately upon contacting the water's surface; contact fuses detonate.
• Since HE shells detonate on contact, blast effects are applied centered on the point of impact, possibly damaging ship modules (and even detonating magazines). SAP shells detonate, but having no blast radius, have no such effect.
• Like solid armor, seawater has a normalization effect. The trajectories of AP ordnance (shells, bombs, rockets) become more horizontal, between 2º and 6º depending on a global parameter for each weapon.
• Water drag is much greater than air drag. It slows down AP ordnance based on a coefficient for each weapon.

As the shell (etc.) slows, it loses energy. Thus penetration decreases significantly over distance. However, the shell may still retain enough energy to penetrate a ship before the fuse timer expires, especially if it just happens to encounter a lightly armored section of the hull. Underwater penetrations do not cause flooding.

Knowing that seawater is essentially liquid armor, armor systems designers save weight by providing little armor protection more than a meter or two below the waterline. Ships with torpedo protection systems likely will absorb such a hit in the torpedo bulge. Small ships such as destroyers with no armor to speak of may be 'penetrated' by a shell that would otherwise 'overpenetrate'.