Evading Destroyers

A walkthrough of the game mechanics surrounding how destroyers detect and attack submarines, and the counter methods available to a submarine to escape.

Overview

Sooner or later, anyone who plays silent hunter 4 is likely to be detected by a destroyer. What follows is all the information you need to understand how you are being detected, what to do about it, and how to avoid it in the future. I also cover some of the game's torpedo mechanics, with a particular focus on how they apply to a closing destroyer, should you find the need to actively defend yourself.

Destroyers are hard to kill, but far from impossible to survive, and using the information I have laid out here, you can learn to take the fight back to them.

This information will apply more or less to anyone, no matter what difficulty settings they use. My final scenario, where you are detected in shallow water will be more difficult without contact updates and external camera, but I have done my best to make sure all this advice will apply to anyone, including people playing on 100% difficulty.

Mechanics (detection and evasion)

Destroyer Sonar:
Destroyers have two types of sonar, active and passive. In active mode they are sending out pings and listening for the return. In passive mode, they are listening for the noise your ship generates.

The sonar system of a destroyer can determine the the angle of a noise in three dimensions.

Destroyer sonar is only effective in a frontal arc of something like 120-140 degrees on the xy plane and some unknown angle on the z plane (x and y are your surface dimensions. z is depth). Destroyers have a harder time detecting targets to their sides, rear, and directly underneath them. This applies to both passive and active modes.

Noise:
Noise is not your friend. You should always make as little of it as possible when around sonar equipped ships. I recommend sticking to 1/3 speed only (3 knots). You should also go to silent running to reduce general noise level, and prevent repairs and torpedo loading, both of which are very loud. If you find yourself very close to a destroyer, you need to stop. I don't know if this game considers noise made by rising or sinking, but to play it safe, I stop this as well unless I need to sink to prevent a collision.

Thermal Layer:
The thermal layer is a temperature gradient, where water at two different temperatures meet. This causes some of the sound passing through this region to be reflected, and the remaining noise to be somewhat refracted. This reduces the intensity of sound made on one side as heard by someone on the other side. A destroyer will hear you below the thermal layer if you are reloading torpedoes or moving at flank speed, but at silent running and moving at 1/3, they will not be able to get an accurate read on you, if they can detect you at all. This also reduces the effectiveness of active sonar. This is your primary means of escape once detected.

Decoys:
I'm going to cover this here rather than tell you exactly when to use them in specific scenarios. Decoys don't work by making noise, and are entirely useless for defeating passive sonar. Instead, the bubbles a decoy creates work much like the thermal layer, but better. They reflect sound, in this case, active sonar. This reflection will make it look like there is a ship located where the decoy is. They will however still be able to detect you as well, and are best used when facing multiple destroyers to reduce the intensity of depth charging, giving you a better chance at escaping.

Mechanics (torpedoes)

This is not a comprehensive guide on torpedoes, just some information that is particularly relevant to defensive uses.

Mk 10:
This torpedo is slow, has a short range, and a smaller warhead than the Mk 14. It is however extremely reliable, and the only torpedo in the game with a contact detonator that works at shallow angles. It has a 1% failure rate from 0 (perpendicular) to 70 degrees, after which it has only a 25% chance to not detonate.

These torpedoes are useful when fired at a ship closing straight at you, as they are likely to detonate even when hitting the angled bow of a ship head on, an angle too steep for other torpedoes.

Mk 14:
This torpedo is kind of terrible, but you'll probably use this torpedo or the similar Mk 23 a lot. What is important to know about this torpedo is that the slow setting halves the chance of a non detonation on impact. When firing at a closing ship with this torpedo, always use the slow setting and the contact/influence setting, to maximize your chance of a detonation. Some people may to prefer to run Mk 10's in the rear tubes for defensive use.

Mk 16:
This is the least reliable torpedo in the game, though it is ideal for harbor raids having a very long range and the largest warhead. These torpedoes are entirely unsuited for defensive use, and so carrying them in the aft tubes is not recommended.

Mk 18:
This torpedo is eclectic and does not create a wake. It does however have the same issues with steep impact common to all other torpedoes, except the Mk 10.

Mk 23:
The Mk 23 is exactly as reliable as the Mk 14, but does not have the slow setting. It does however have a slightly larger warhead. I favor the Mk 14 because of the slow option.

Mk 27:
I don't really like this torpedo. The reality is that, at least defensively, it's just too slow, and destroyers will almost always be able to go around them (or outrun them, depending on the angle). Defensively, the best time to use them is likely when a destroyer is making a sharp turn after depth charging you, as it will be going relatively slow and heading back towards your torpedo.

Torpedo Spreads:

I think many people default to the arrow shape spread, firing inside to outside, alternating sides. This is actually the easiest spread to dodge. If the lead torpedo is spotted it gives maximum time to dodge the flanking torpedoes in the spread.

Instead, your default should be the opposite, shooting the outside angles first and working in, or a side to side spread where your torpedoes create a diagonal line. In both cases, start with the side of the spread that is leading the target to make it as hard as possible to evade.

For a target closing straight at you, I use a hybrid spread, firing the far shot on one side of the spread, then working my way side to side starting at the other side, with the aim that the first shot will steer the enemy into the "wall" created by the remaining torpedoes.

If you are detected (Passive)

If you are not being pinged, then you are facing passive sonar and stealth is still your best friend. Keep the engines at 1/3, start diving for the thermal layer, and take evasive action by turning. Making noise at this stage will just make it easier for destroyers to accurately depth charge you, which you want to avoid. After the initial pass by the enemy, they will lose you as you move out of their effective sonar area (this actually happens slightly before they reach you if you are deep enough), and it will be difficult for them to find you again (accurately. They may still know generally where you are) unless they get you back in the sonar cone.

Once you pass the thermal layer, you need to run slow and deep. It can take several hours for the destroyers to completely lose you and give up the search. I'd wait another hour or two if possible before rising up to periscope depth and preparing to surface.

If you are detected (active)

If you hear pings, then things are now more dangerous for you than when facing passive sonar. A destroyer pointing at you and using active sonar will know exactly where you are, and will be able to depth charge you with considerable accuracy. As a point of interest, a ship using active sonar will not be able to listen for you passively, though this knowledge is unlikely to be helpful.

As soon as you hear a ping, go to flank speed and start diving and turning. Flank speed give you the possible performance for evasive action, and will cause you to dive faster. If the pinging stops, or you hit the thermal layer, immediately go back to 1/3 speed. Do not however slow down simply because a destroyer has passed over you and you are in their blind spot. They still know pretty much where you are and being silent does nothing to defeat their active sonar once they turn around. While not required, you can reduce drag on your submarine and shorten the time needed to turn in the other direction by not making full turns to either side. Instead of maximum turns, consider limiting the rudder to 30-35 degrees, particularly after the first turn.

Once you're below the thermal layer, you are using the same end strategy as with passive. Run slow and deep until you have lost all sonar contacts for some time, go to periscope depth to make sure everything is safe, and finally surface.

If you are detected (shallow water)

If you are detected while in shallow water, understand that ♥♥♥♥ has hit the fan and you are fighting for your life, and the life of your crew. Without being able to go below the thermal layer, you will likely not be able to lose someone using active sonar, and are unlikely to hide from even passive sonar for very long.

The most common reason to find yourself in this situation is a port raid or survey mission. If you are ever closing on a port and it has two or more sonar equipped ships, turn around and leave. If detected, you are facing a fight with no hope for survival, and you are worth more to your country alive.

Against a single destroyer, a good offense may be your best defense. However, you will need to leave quickly as attacking a destroyer will cause the enemy to call for reinforcements, and may cause docked ships to become active. If you attack and fail (dud hit), you will have given away your position and your best hope of survival.

If worst comes to pass and you are detected in the shallows, there is really no winning game plan. You're going to have to do your best with the resources and circumstances available to you. I do however have some considerations for you in addition to the information already provided in the mechanics sections to get you pointed in the right direction.

First, if you are rammed, you will not make it home. If rammed, you'd be lucky if you don't have to surface immediately to control the damage and flooding, and you'll likely take extensive damage to propulsion that you can't repair. This makes periscope depth shallows where you can't go any deeper extra lethal.

If you fail to sink or disable a destroyer who has detected you in shallow water, you'll have to make a run for it. Until you can get down at least 40-50m, agility is going to be more important than stealth. You need to avoid being rammed, and try to prevent good depth charging runs on your submarine. If you don't want to use, or have disabled, the external cam, leave the periscope up until you can at least get the conning tower 6m under water so it won't be hit.

If the enemy doesn't use active sonar, you have a chance to try and run as deep as possible at 1/3 speed and hope the enemy doesn't get a good bead on you. This will however take some time because you won't be able to use much if any time compression until deeper waters. If they do use active sonar, then you are usually better off staying loud and fast and trying to survive long enough to at least try the torpedoes again.

As a final note, the maximum launch depth for torpedoes isn't periscope depth (14-18 metres for American Subs). Every Submarine in the American fleet can launch torpedoes down to 30 metres. Now, I don't expect anyone to work out the math for launching a torpedo using only your sonar, but if you are carrying Mk 27 homing torpedoes, you may consider launching them blind in the direction of the enemy, especially one who has just passed over your general area.

Good Luck!



Updated: Aug 8, 2016

• Cleaned up some wording, grammar, and spelling errors.
  
• Added note about American submarine torpedo launch depth.

[Fimpen]

An eclectic torpedo?! What is this nonsense? Just kidding. A typo on the Mk 18 (should be "electric"). Sweet guide, dude. Some really good advice.

There's a tactic in SH3, that I can't remember if it works in SH4. What you do is once the destroyer stops pinging (i.e. just before it drops depth charges), you dive deep (80+ meters) at flank speed. Maybe turn a bit, but it might slow you down.

Once he comes back after determining your depth again, you do the exact opposite. Go shallow at flank speed, to maybe 30 meters or so. Worked fine for me. I was able to dodge depth charges all day. Maybe someone can chime in on this, or test it.

[Frosty007R]

CRASH DIVE Duology gamer here, this review has put Wolves of the pacific on my hotlist. Well done!

[wizzzaap]

I remember a harbour raid that went wrong, I was forced to surface and engage a pair of destroyers in a gunnery duel. I had no right to win but got lucky with a hail mary torpedo salvo on one and managed to stay under the guns of the other. it turns out that if you get close enough to some destroyers they can't actually depress their guns enough to shoot you.

basically, if you are forced to surface right next to a destroyer stay as close as you can and just keep pumping shells into her, it may be your only chance.

[Foxxhound]

@Randox

Thanks for the timely response. Those two errors literally made the guide almost unreadable.

[Randox]

@Foxxhound Glad to know people are still finding this useful. Also, you're absolutely right strait vs straight, so I've gone ahead and corrected that. Appologies to anyone who ever tried to run this through a translator and got supper confused

[Foxxhound]

Love the detail. Very helpful in understanding how the enemy operates.

One thing I want to point out though is that you used the word 'strait' when you should have used the word 'straight.' That's 'straight,' with a 'G.' 'Straight' is an adjective describing something that does not turn, such as a destroyer heading directly to your position after detecting you on active sonar. A 'strait' is a noun describing a narrow body of water between two bodies of land, such the Makassar Strait or the Strait of Malacca.

[neededlotus5]

I have gone toe to toe with destroyers on the surface and won by using my deck gun with minimal damage to my sub no need to evade the ai is as blind as a bat

[R2T2]

Many thanks, very useful information.

[Randox]

You can search for Thermocline to find a more detailed explanation of the phenomenon. In simple terms, it's where there is a sudden drop in water temperature vs depth. The cold water is more dense as well, so there is a very rapid increase in density. Speed travels faster in a more dense medium, and long story short, this causes sound waves to refract upward. Sound waves traveling down are essentially reflected at the boundary where the water temperature rapidly drops.

In the game, one of the crew says "passing thermal layer" when descending through jt. You want to be a bit under it to be safe, and it's important to stay quiet (it sends *all* noise upward). You may not hear this line if using time compression, so stay in real time during the dive.

I don't think there is any way to actually check, and it doesn't exist everywhere (shallow water has no thermal layer).

[YourHolinessVonGustav]

Randox, could you please explain more about Thermal Layer? What it is and how can I know if I am below it?
Thanks