Anti-Submarine Warfare (ASW)

Anti-submarine warfare (ASW) in World of Warships concerns the methods of locating, dealing damage to, and avoiding damage from submarines. This includes using consumables and other mechanics to locate a submarine, as well as using various weapons to damage a submarine.

==Finding a Submarine==
The two primary means of finding a submarine are fuel spills and emitted sonar pings. Other methods include consumables such as {{Hydroacoustic Search}} and {{Surveillance Radar}}.

===Fuel Spills===
When a submarine is hit at periscope or maximum depth from any armament, she begins to leak fuel (oil) that rises to the surface, regardless of whether she is detected or undetected. Fuel spills last for 40 seconds, and are the best way to pinpoint a submarine’s location, as they always leak from the exact location of a submarine, unlike sonar ping emissions. They are also visible from any range.

===Ping Launch Emission===
When a submarine uses its sonar, a visual effect appears within a 1 km radius of her, lasting five seconds. In addition to this visual effect, the actual sonar ping moving across the map is visible to ships within 8 km. In combination with the ping launch effect, it allows surface ships to get a general idea of the location of the submarine. It is generally not as accurate as fuel spills, as the ping launch effect is only accurate within 1 km. In addition, the moving sonar ping is not visible outside of 8 km. Finally, each ship sees only sonar pings within her acquisition radius (i.e a ship cannot see the sonar pings launched against an ally on the other side of the map).

===Consumables===
Against submarines on the surface or periscope depth, the {{Hydroacoustic Search }} consumable is perhaps the best offensive and defensive tool against submarines, as it detects them all the way to maximum depth (albeit only at a range of 2 km at maximum depth), as well as detecting their torpedoes before they would otherwise become visible. The consumable’s long duration also helps as a submarine deterrent.

The {{Surveillance Radar}} consumable detects submarines only at surface depth. It is unable to detect them at periscope and maximum depth. It can be useful for a quick update on a submarine’s position, but its limited use makes it a poor tool against submarines.

The {{Submarine Surveillance}} consumable, available to all submarines (except ''[[I-56]]'') and tech-tree Tier V+ Commonwealth, Japanese and Italian cruisers, is also an effective tool against underwater submarines<ref name="underwater submarines">“Underwater submarines” refers to submarines at periscope and maximum depth.</ref>. However, the version found on submarines has a long preparation time, making it unavailable for them in the early game. Submarines are unable to detect each other at maximum depth without it.

While the {{Hydrophone}} consumable does not detect submarines, it does highlight their position (their silhouette) in the game world if they’re at surface or periscope depth. It also updates their “last spotted position” on the minimap.

==Killing a Submarine==
The primary ASW weapons are shipborne depth charges and airborne (via [[#Depth Charge Airstrikes|air strikes]]) depth charges. Other weapons (varying in effectiveness) include main battery and secondary guns, airborne rockets and bombs, and torpedoes.

===Splash Damage===
Because water is incompressible, the energy from an underwater explosion propagates outward in the form of a spherical shock wave, dispersing energy as the sphere expands. The energy at a given point on the sphere depends on the initial energy and the distance from the explosion. High enough energy will cause damage to the target. Thus unlike surface ships a direct hit is not necessary. “Close enough” applies with depth charges as it does with horseshoes.<ref>[https://en.wikipedia.org/wiki/Horseshoes Horseshoes, the game.]</ref>

In order to simplify the physics, the sphere is represented as concentric circles with the center at the explosion and the radius &mdash; the '''splash radius''' &mdash; at the farthest distance that damage is done. Within that radius, the '''splash damage''' is uniform (a simplification for game purposes), and decreases in each circle. With this comes a '''splash damage coefficient''' assigned to all weapon types in the game (except torpedoes), that affects the overall damage dealt to a submarine within the splash radius.

Introduced to model damage from underwater explosions, '''splash damage''' works by giving each shell and bomb a splash radius and splash damage coefficient. '''Splash radius''' is determined mostly by caliber for shells, bombs and rockets &mdash; the larger they are, the larger the radius. In terms of shell types, HE and SAP shells have large splash radii, while AP shells of the same caliber have approximately half their splash radius. The splash radius of depth charges from ships and aircraft is fixed.

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    <div>&mdash;&mdash;&nbsp;&nbsp;'''Splash Radius Data'''&nbsp;&nbsp;&mdash;&mdash;</div>
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{{Ship:Splash Radius Data}}
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The '''splash damage coefficient''' affects the amount of damage a submarine receives from indirect hits. Splash damage against submarines is calculated with the formula '''Alpha Damage * Splash Damage Coefficient'''. Alpha damage is the maximum damage of an armament listed in the port. The splash damage coefficient of various armaments is listed below.

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    <div>&mdash;&mdash;&nbsp;&nbsp;'''Splash Damage Coefficient Data'''&nbsp;&nbsp;&mdash;&mdash;</div>
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{| class="wikitable sortable" style="text-align:center; margin-left: auto; margin-right: auto; border: none; width:750px"
! colspan="2" style="text-align:center; padding:6px;"| Depth Charges Splash Damage Coefficients
|-
! style="vertical-align:middle; width: 100px;" class="unsortable" | Armament
! style="vertical-align:middle; width: 100px;" class="unsortable" | Splash Damage Coefficient
|-
| style="vertical-align:middle;" | Ship-mounted Depth Charges
| style="vertical-align:middle;" | 1.0 (From 0.0 m to 120 m); <br> 0.33 (From 120.1 m to 800 m)
|-
| style="vertical-align:middle;" | Airstrike Depth Charges (Cruisers & Battleships)
| style="vertical-align:middle;" | 1.0 (From 0.0 m to 150 m); <br> 0.50 (From 150.1 m to 300 m); <br> 0.0 (From 300 m to 375 m)
|-
| style="vertical-align:middle;" | Airstrike Depth Charges (Ägir, Mengchong & Siegfried)
| style="vertical-align:middle;" | 1.0 (From 0.0 m to 96 m); <br> 0.45 (From 96.1 m to 240 m); <br> 0.0 (From 240.1 m to 300 m)
|-
| style="vertical-align:middle;" | Airstrike Depth Charges (Aircraft Carriers)
| style="vertical-align:middle;" | 1.0 (From 0.0 m to 300 m); <br> 0.50 (From 300.1 m to 480 m); <br> 0.0 (From 480.1 m to 600 m)
|}
<br>
{| class="wikitable sortable" style="text-align:center; margin-left: auto; margin-right: auto; border: none; width:750px"
! colspan="2" style="text-align:center; padding:6px;"| Shell & Bomb Splash Damage Coefficients
|-
! style="vertical-align:middle; width: 100px;" class="unsortable" | Armament
! style="vertical-align:middle; width: 100px;" class="unsortable" | Splash Damage Coefficient
|-
| style="vertical-align:middle;" | AP Shells
| style="vertical-align:middle;" | 0.1
|-
| style="vertical-align:middle;" | HE Shells, SAP Shells, AP Rockets, AP Bombs, HE Bombs, Skip Bombs, Dutch Airstrikes
| style="vertical-align:middle;" | 0.165
|}
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{{block|i|content=Example: A submarine is hit by an airstrike depth charge from 200 meters away launched by ''[[Vermont]]''. 

Alpha damage of ''Vermont''’s Depth Charge Airstrike: 4,900

Splash damage coefficient at 200 meters: 0.50

Damage taken: 4,900 X 0.50 = 2,450}}

{{block|i|content=Example: A submarine at periscope depth is hit within the splash radius (i.e. not a direct hit) of a single AP rocket from ''[[Manfred von Richthofen]]''.

Alpha damage of ''Manfred von Richthofen''’s AP rockets: 3,100

Splash damage coefficient of AP rockets: 0.165

Damage taken: 3,100 X 0.165 = 512
}}

===Depth Charges===
[[File:Ammo_depth_charges.png|frameless|left|link=]]Found on almost all Tier V+ destroyers, and some Tier V+ cruisers, ship-mounted '''depth charges''' can be thought of as “underwater bombs”, designed to deal damage to submarines at all depths, and cannot damage other classes. Depth charges have a low flooding and fire chance, and rely on direct damage to deal with submarines. All depth charges have a 40 second reload time per charge, and an 800 meter splash radius. They also have an increased chance to disable a submarine’s sonar. Within a 120 meter radius, depth charges have a splash coefficient of 1. Past this range, they have a splash coefficient of 0.33.

Depth charges mounted on cruisers and destroyers vary in their drop pattern and the location of the mount. Both can be found in the table below.

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    <div>&mdash;&mdash;&nbsp;&nbsp;'''Depth Charge Data'''&nbsp;&nbsp;&mdash;&mdash;</div>
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{{Block|i|content= As there is currently no reticle for shipborne depth charges, a common tactic is to use depth charges at the beginning of the battle and observe their drop pattern. This way, one won’t be caught off-guard when attacking a submarine with them.}}

{{Ship:Depth Charge Data}}
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[[File:Daring_Depth_Charges.png|200px|thumb|The damage distribution of ''[[Daring]]''’s depth charges (cr. WoWs Shipbuilder)]]

When a depth charge from a ship is launched and hits the water, it becomes “active”. It falls at a base 10 knot speed, which is randomized by a multiplier of anywhere from about 0.8 to 1.2 times. It then explodes after a 7 second timer, which is also randomized by a multiplier of anywhere from about -0.5 to +0.5 seconds. This means the detonation depth at the end is random (from about 139.6 to 241.7 meters). The depth at which a depth charge detonates can be calculated by multiplying the fall speed, detonation timer and the travel speed in meters/second (1 knot = 2.6854 m/s). Shipborne depth charges explode at a much deeper depth than those from airstrikes.

Generally speaking, while ship-mounted depth charges have better potential damage over airborne depth charges, the fact that cruisers and destroyers have to risk their hull to attack a submarine with them limits their effectiveness. More often than not, it is not worth it for said classes to go out of their way to strike a submarine with depth charges, unless there is little risk of being attacked by enemy surface ships or aircraft. In addition, enemy submarines can also shotgun<ref name="shotgunning">Shotgunning is the act of getting to point-blank range of a ship (either stationary or moving towards you), and launching unguided torpedoes at it, often crippling or destroying the ship.</ref> an approaching ship (or simply dive away either vertically or horizontally)<ref>The depth of submarines is displayed in a value known as ship_m. To convert to actual in-game meters, multiply the value by 2 (i.e. Submarines have a maximum depth of 120 ship_m = 240 m in the game, though the most a player can dive to is 60 ship_m = 120 m).</ref>, further increasing the risk of using this type of depth charge effectively.

{{Block|i|content= Example: A single depth charge from ''Daring'' drops at 9 knots (determined randomly), and explodes after 6.9 seconds (also determined randomly).

9 * 6.9 * 2.6854 = 166.7 meters at which the depth charge explodes.}}

===Depth Charge Airstrikes===
[[File:Ammo_airsupport_depthcharge.png|frameless|left|link=]] With the development of aviation, it became clear that aircraft made not only a great vehicle for traveling large distances, but also for scouting and attacking enemies. Patrol aviation became necessary to defend a country’s coastlines and shipping, as well as attack enemy submarines. Flying boats became the prime means of conducting these tasks, due to their ability to land and takeoff at sea, the vast amount of bodies of water, and low engine reliability of early aircraft. Equipped with searchlights, radar, and depth charges, they became a major threat to submarines throughout the course of World War II.

Found on all Tier V+ battleships, all Tier VI+ aircraft carriers, and some Tier V+ cruisers, '''Depth Charge Airstrikes''' (aka ASW airstrikes) are the other, arguably superior anti-submarine weapon in the game. They operate similarly to airstrikes on Dutch cruisers, where after a delay, they arrive at the designated area to drop their payload, but cannot spot ships or deal damage to other classes. Like shipborne depth charges, they have a low fire chance, but all depth charges from airstrikes have a 100% chance of causing flooding<ref>The actual flooding chance assigned to Depth Charge Airstrikes is 300%. As submarines have no torpedo protection, they will always be flooded when hit with an airborne depth charge, regardless if it deals full damage or splash damage. However, they can only have one active flood at a time.</ref>, as well as an increased chance of incapacitating a submarine’s sonar. Depth Charge Airstrikes on cruisers and battleships have a 30 second reload, with a 375 meter explosion radius (300 meters in the case of ''[[Ägir]]'', ''[[Mengchong]]'' and ''[[Siegfried]]''). Depth Charge Airstrikes found on aircraft carriers have a 25 second reload with almost double the explosion radius, at 600 meters. In addition, the Depth Charge Airstrike on aircraft carriers is automatically controlled, activating when a submarine is detected, leaking fuel or emitting pings within the airstrike’s range. The full characteristics of Depth Charge Airstrikes are listed below:

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    <div>&mdash;&mdash;&nbsp;&nbsp;'''Depth Charge Airstrike Data'''&nbsp;&nbsp;&mdash;&mdash;</div>
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{{Ship:Depth Charge Airstrike Data}}
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Within a 150 meter radius, airborne depth charges from battleships and cruisers have a splash coefficient of 1.0. From 150.1 to 300 meters, the splash coefficient is 0.50. From 300.1 to 375 meters, the splash coefficient is 0.0, however they can still disable a submarine’s sonar at this range. For ''Ägir'', ''Mengchong'' and ''Siegfried'', the splash coefficient is 1.0 within a 96 meter radius, 0.45 from 96.1 to 240 meters, and 0.0 from 240.1 to 300 meters, but they can still disable a submarine's sonar at the outermost range.

For aircraft carriers, within a 300 meter radius, airborne depth charges have a 1.0 splash coefficient. From 300.1 to 480 meters, they have a 0.50 splash coefficient. From 480.1 to 600 meters, they have a 0.0 splash coefficient, however they can still disable a submarine’s sonar at this range.

[[File:Vermont_ASW.png|200px|thumb|The damage distribution of ''Vermont''’s Depth Charge Airstrike (cr. WoWs Shipbuilder)]]

[[File:Siegfried_ASW.png|200px|thumb|The damage distribution of ''Siegfried''’s Depth Charge Airstrike (cr. WoWs Shipbuilder)]]

[[File:Midway_ASW.png|200px|thumb|The damage distribution of ''[[Midway]]''’s Depth Charge Airstrike (cr. WoWs Shipbuilder)]]

Similar to shipborne depth charges, airborne depth charges become “active” as soon as they hit the water. They fall at a base speed of 3.5 knots, randomized by a factor of about 0.8 to 1.2 times. It then explodes after a 4 second timer, which is also randomized, at a factor of about -0.5 to +0.5 seconds. Therefore, detonation depth is also random (from about 26.3 to 50.8 meters). Like shipborne depth charges, the explosion depth of airborne depth charges can be calculated by multiplying the fall speed, detonation timer and the travel speed in meters/second (1 knot = 2.6854 m/s). Depth charges from aircraft explode closer to the surface than ship-launched depth charges.

Depth Charge Airstrikes provide a consistent source of attacking submarines, due to the armament’s quick reload and long range, especially for battleships, and &mdash; in the case of those on aircraft carriers &mdash; the high accuracy. If a submarine is detected or showing signs of its presence through fuel spills or sonar ping emissions, captains should make sure to use this armament as soon as possible against a submarine.

{{Block|i|content=Example: A single depth charge from ''Vermont'' drops at 4.2 knots, and explodes after 3.5 seconds.

4.2 * 3.5 * 2.6854 = 39.4 meters at which the depth charge explodes.}}

===Other Weaponry===
HE and SAP shells are the most effective shell types against submarines, as they have a large splash radius compared to AP shells (almost twice as large), as well as exploding on contact with armor, of which submarines have very little of. However, as HE and SAP shells have a splash damage coefficient of 0.165, underwater submarines<ref name="underwater submarines" /> have almost comparable durability to that of French destroyers and their unique HP saturation mechanic (the value of 0.165 being, in fact, identical to that of saturated parts of a ship’s hull). AP shells have a splash coefficient of 0.1, further limiting their effectiveness against underwater submarines. In regards to armor penetration, submarines follow the same rules as other classes, even when the shell arms by hitting the water and penetrates afterwards.<ref>[[Ship:Armor_Penetration#Water_.28Liquid_Armor.29|Water (Liquid Armor)]]</ref>

Secondaries are usually unreliable for directly killing a submarine, but can force them to dive underwater. They are also useful for forcing a fuel spill from a submarine, due to their high rate of fire.

Regular ship- and airborne torpedoes can hit submarines at surface and periscope depths, but are generally ineffective as they lack a splash damage coefficient, requiring direct hits to deal damage. While airborne torpedoes are dropped at closer distances, a submarine is likely able to dive to escape damage. Finally, for ship torpedoes specifically, the distances at which they typically are launched means submarines will have ample time to avoid them by diving. Deepwater torpedoes do '''not''' hit submarines at any depth. Homing torpedoes, however, are a submarine’s best weapon against other submarines, due to the short distance at which their homing shuts off, combined with their homing capability.

The HE bomb airstrikes of Dutch ships deserve a special mention, as they can do heavy damage to surfaced submarines due to the large drop area size and amount of bombs dropped, as well as the large splash radius. However, it is just as easy for submarines to avoid airstrikes by diving, making this armament type unreliable against submarines. Indeed, one should not actively use this armament against submarines.

For aircraft carriers, their automatic ASW is arguably their best source of damage against submarines. The high accuracy of the airstrike combined with their large explosion radius means they can cripple if not destroy submarines who wander too close. For offensive purposes, rockets and bombs will prove useful to at least force a submarine to dive, due to their (usually) quick aiming nature. However, they are subject to the same 0.165 splash damage coefficient as HE shells, limiting their effectiveness against periscope depth submarines. In addition, their splash radius is usually very small (for comparison, ''[[Tachibana]]''’s 76 mm AP shells have a splash radius ~3 times larger than most rockets and bombs), increasing their difficulty in dealing damage to submarines. Dropping a fighter on top of a submarine can also force them underwater, as a submarine will usually want to remain undetected to avoid enemy fire, as well as avoid a carrier’s ASW.

==Upgrades & Commander Skills==

Some upgrades and commander skills enhance combat capability against submarines:

{{Depth Charges Modification 1}} adds two charges to the depth charge armament (i.e. a ship with 2 charges of the depth charge armament is increased to 4. It does not increase the amount of bombs in a single charge).

{{Airstrike Modification 1}} increases the damage of airborne depth charges by 15%, as well as reducing the reload of airstrikes by 20%.

[[Ship:List_of_Commander_Skills#Demolition_Expert_2|Demolition Expert]] on destroyers, cruisers and battleships increase the splash radius of shells by 15%.

[[Ship:List_of_Commander_Skills#Extra-Heavy_Ammunition|Extra-Heavy Ammunition]] on destroyers increases depth charge damage by 10%.

[[Ship:List_of_Commander_Skills#AA_Defense_and_ASW_Expert_2|AA Defense and ASW Expert]] on cruisers and battleships increases depth charge damage (both ship- and airborne) by 10%.

[[Ship:List_of_Commander_Skills#Secondary_Armament_Expert|Secondary Armament Expert]] on aircraft carriers increases the damage of depth charges from the automatic ASW aircraft by 10%.

{{Block|i|content=The Radio Location skill gives a bearing to a submarine if it is at surface or periscope depth. It does not work if the submarine is at maximum depth.}}

==Defense Against Submarine-Launched Weapons==

===Against Homing Torpedoes===
When dealing with homing torpedoes, the most common tactic is to slow down and/or turn in or out. For battleships in particular, they have it the easiest: Homing stops at the greatest distance for the class (2.1 km for single pings, 1.6 km for double pings in the case of Tier X submarines<ref>For more information about the distances homing stops at, visit the [[Ship:Torpedoes#Acoustic_Homing_Torpedoes|Acoustic Homing Torpedoes section]] of the Torpedoes page.</ref>), and more often than not the simple act of slowing down is enough to dodge torpedoes at long ranges. As soon as a battleship spots torpedoes, they should slow down and turn in. {{Damage Control Party}} should ideally be used if you are pinged and homing torpedoes are spotted heading towards you, and not immediately when you are pinged. However, if there is a risk of being set on fire or being flooded, it may be best to hold the usage of one’s {{Damage Control Party}}. In addition, battleships have strong ASW, with the longest reach and second-hardest hitting Depth Charge Airstrikes, behind aircraft carriers. Therefore, once pinged, battleship captains should be on the lookout for the ping emission effects, using them in tandem with fuel spills to locate and deal damage to submarines.

Cruisers and destroyers have it harder, as the homing distance is much closer. In addition, if a submarine lands a double ping, the homing distance cutoff is decreased by half. Both of these classes also have a very short {{Damage Control Party}} duration, enabling submarines to quickly re-ping them. The same tactics as battleships apply, but it will be harder to pull it off. In addition, cruiser Depth Charge Airstrikes are weaker than battleships, particularly their range is significantly shorter. While you can still look out for signs of submarines, more often than not they will be out of your range to use your ASW. Cruisers and destroyers with depth charges should only actively try to deal with the submarine if no other ships present an active threat to them, and if they can minimize the risk of being shotgunned by a submarine.

Aircraft carriers initially have a long immunity duration against homing torpedoes, due to their automatic [[Ship:Consumables#Damage_Control_Party_2|Damage Control Party]] that lasts a long time. Once the duration runs out, however, they can be easy prey for submarines. If a submarine is within range and spotted or showing a sign of its location, an aircraft carrier’s automatic ASW will keep it wary, due to the large AoE radius and almost pin-point accuracy. However, it is likely an aircraft carrier will have to rely on their team’s assistance in dealing with a skilled submarine intent on hunting them, especially if the submarine is at a range greater than a carrier’s ASW.

As submarine homing is the strongest against the class itself, submarine-vs-submarine combat is generally risky, and should ideally be avoided unless necessary and if a submarine has allied support. If engaged in combat with another submarine, captains should not only use their [[Ship:Consumables#Damage_Control_Party_3|Damage Control Party]] wisely, but also change depths and course to dodge homing torpedoes. In addition, underwater submarine-vs-submarine combat relies on one’s {{Submarine Surveillance}} to spot the submarine.

===Against Conventional/Unguided Torpedoes (AKA “Shotgunning”)<ref name="shotgunning" />===

In dealing with submarines who do not use their homing capabilities, it is much harder to counter them. If no sonar ping is emitted, there is no warning that a submarine is approaching (unless one uses a consumable to detect them, or the submarine is leaking fuel). Their stealth at the surface and complete invisibility at maximum depth also makes them tricky to deal with.

In general, one should be on the lookout for a submarine’s whereabouts at all times. Captains should pay attention to where a submarine was last spotted on the minimap. Consumables like {{Hydroacoustic Search}} and {{Surveillance Radar}} will help in providing recent updates to a submarine’s position, as well as potentially a deterrent in a submarine making shotgun attacks. One can also try slowing down when a submarine is preparing to shotgun, in an effort to avoid their torpedoes.

The unfortunate reality, however, is that there is very little &mdash; if anything &mdash; one can do in mitigating damage from an above-average submarine player who chooses to primarily rely on shotgunning in dealing damage to ships.

==Sources==
* [https://www.reddit.com/r/WorldOfWarships/comments/uby36e/how_splash_damage_and_depth_charges_work_against/ How Splash Damage and Depth Charges Work against Submarines] (Some outdated values)
* [https://worldofwarships.com/en/news/general-news/submarines-again/ Submarines Are Again Lurking in the Depths of Our Seas for Testing Purposes]
* [https://app.wowssb.com/ WoWs Shipbuilder]

==Notes==
<references />