Basic Submarine ASW Combat Tactics

[Molon Labe]

Overview
Previous articles in this forum have addressed task-specific tactics, such as weapons employment (http://www.commanders-academy.com/forum/showthread.php?t=63) and torpedo evasion (http://www.commanders-academy.com/forum/showthread.php?t=47). Instead of being focused on specific tasks, this topic is dedicated to tactics employed throughout the battle. This topic discusses combat tactics for a situation where one sub faces off against another sub of the same class. There are no other combatants present is this situation. A later thread will build on the tactics discussed in this topic to be applied when the subs are of different classes. All specifications used in this post will be for DW 1.04 + LWAMI 3.08, unless stated otherwise.

Just like a story, a sub v. sub battle has a beginning, a middle, and an end. The beginning is the detection phase, where your primary goal is to detect your opponent while preventing counterdetection. The middle is the tracking phase, where your main concerns are to classify and localize your opponent, while preventing counterdetection or preventing him/her from localizing you. The end is the engagement phase, where your goal is to deliver a weapon to the target, while preventing counterdetection, preventing localization, and/or evading incoming weapons.
The progression of events during these phases can be understood as a race, with the moment of torpedo impact being the finish line. But this is not a track race where you run as fast as you can in your own lane—this is a race where your actions have an impact upon how fast your opponent can reach the finish line as well. Effective tactics are therefore not designed simply to move your towards the finish line, but to keep your opponent away from it.

[Molon Labe]

Detection Phase


The clever combatant imposes his will on the enemy, but does not allow the enemy's will to be imposed on him.

Your first task is to detect your opponent while preventing counterdetection.

The DW Acoustics Model:
Detection in DW is a fairly simple phenomenon. A (target) sub has a variable source level (SL), which represents the amount of sound it puts in the water. The faster the sub goes, the higher the SL. Signal strength equals the SL at zero range, but as range increases, signal strength decreases (“transmission loss”). The rate at which signal strength decreases with range varies depending on the acoustic environment. Signal strength decreases slowly in a bottom limited SSP with a rock bottom, in a surface duct SSP inside the surface duct (above the layer), and on both sides of a convergence zone SSP. Signal strength decreases quickly in a bottom limited SSP with a mud or sand bottom (sand is worse), and in a surface duct SSP below the layer. Higher sea states can also accelerate the loss of signal strength. If the sound must cross the layer to be heard, there is a dramatic loss of signal strength. In a convergence zone SSP, the loss of signal strength is reduced sharply in very small bands (probably less than 1nm long) at 30nm intervals from the source.

It has also been confirmed that cross-layer detection ranges are shorter when the contact is slightly below the layer (http://www.subsim.com/radioroom/showthread.php?t=124973). It is a reasonable hypothesis that is caused by a feature of the acoustic model that causes a lower rate of signal loss at lower velocity parts of the SSP than it does at the higher velocity parts.http://img228.imageshack.us/img228/1672/layergk9.jpg

Sonar sensors have a sensitivity value that determines the minimum signal strength it must receive to report a contact. Sonar sensitivity is reduced by “self noise,” which is caused when ownship speed is above a certain threshold (“washout”), when a torpedo tube is open, when a mast is raised, or when the boat is very shallow. Self noise appears as an increase in “static” on the broadband screens.

To summarize, detection occurs when (SL) - (Transmission Loss) > (Sensitivity Threshold) + (Self Noise). (See? It is simple.)

What that means for tactical purposes is that the greatest detection ranges will result from the loudest (fastest) contacts, in favorable SSPs and in favorable parts of the SSP, when using the most sensitive sonar in the absence of self-noise.

Maximizing sonar performance
At risk of belaboring the obvious, the most important thing you can do to help make sure you detect your opponent before he/she detects you is to be the sub with the lower SL, which means going slower than your opponent. You will certainly detect your opponent faster by patrolling faster because you will cover more area, but you will be speeding up the process for your opponent as well. In a real DW match there may be other concerns that makes a slow patrol speed unreasonable, but for purposes of this topic, slower is always better.

Another obvious point: minimize the amount of time spent at periscope depth or with a mast raised; do not travel around with a torpedo tube door or missile hatch open unnecessarily.

For SSNs, the most effective sensor will be the towed array (TA). The TA need not be deployed to full length to be at maximum effectiveness. For US subs, top performance is reached before 1/4 of the length is deployed. For the Akulas, approximately 200m is enough. In most situations, a shorter TA length is favorable to a longer TA length because it allows for a quicker response to a course change.

All TA’s have a 60 degree blind spot centered directly ahead of it. For the Kilo, the most effective sensor is the conformal array. The conformal array has two 60 degree blind spots, centered fore and aft. These blind spots require you to make frequent course changes of at least 60 degrees to ensure detection of the enemy at the earliest possible time. The intervals are a matter of personal preference, but there are a few general rules to follow: (1) the longer the TA setting, the longer the intervals should be; this is because you may not be able to mark a contact during a turn until the array stabilizes, and you may have to turn back to your prior course before that can happen; (2) the faster you are going, the shorter the interval should be—for the same reason as above in (1), and also because the faster you go the more likely it is that the enemy has entered your detection range during a given time period.

If a thermal layer is present, you will need to regularly search both sides of it. This can be done with obvious way—by changing depth—or, by extending the TA can be below the layer while your boat is slightly above the layer. To do this, slow to 2 knots or less. The process can be sped up by lengthening the TA. Take care not to move the boat backwards if you use reverse thrust to slow down; this will fail the TA.

Sprinting
Sometimes you’re more interested in moving than searching. If this is the case, you must take care to prevent counterdetection while your SL is high. Get behind terrain features whenever possible (of course, “behind” assumes you know the approximate direction of the opponent, which may not be the case). Also, in a surface duct SSP, detection ranges inside the surface duct are significantly longer than they are under the duct. Do your sprint below the layer to minimize the possibility of counterdetection. Because it is likely that your location on the SSP effects detection range as well, you should be only slightly below the layer, at the depth where sound speed is the highest.

Note: The differences between sides of the layer in a Convergence Zone SSP are much more subtle than in the Surface Duct SSP. If anyone has solid data on the differences, please share that information in this thread.

Preparation
The detection phase is slow, so take the opportunity to get a few things done in advance. Check your HPA; if it’s close to 50%, be sure to charge it. Check your CM tubes, load them if they are empty. Check your torpedo tubes; if you do not have ASW weapons loaded, load them immediately. Even if you are on a strike mission and just received word five minutes ago that a sub is in your area, and still have no intention of sinking the sub, replace one of the missiles with a torpedo. Counterfire is an essential part of torpedo evasion.

Adjust your torpedo presets in advance. Make sure the speed settings and floors of your torpedoes are maximized. Set an ASuW safety if desired. Set a search depth that is unlikely to run aground in most of the terrain, and/or set some weapons to search above or below the layer depth as desired. Assign two torpedoes to Snapshot.

Consider getting a UUV out there. Detection of a sub with the UUV is highly unlikely, but if you are fired on, having a UUV deployed will help you rapidly triangulate the position the torpedo was fired from and will make tracking the torpedo much easier. The cost of this is an open torpedo door, which causes a small amount of self noise and might a slightly reduced detection range. The more likely you are to be caught off guard (e.g., you’re sprinting more, there is more terrain around for your enemy to be hiding behind), the more early UUV deployment tends to be a net positive.

[Molon Labe]

The victorious strategist only seeks battle after the victory has been won, whereas he who is destined to defeat first fights and afterwards looks for victory.

Tracking Phase
At this point, you have detected a faint 50, 60, or 125 hz signal which you suspect to be the opposing submarine. Your priority now changes from searching the area to tracking this target, confirming that it is your enemy, and moving into position to deploy weapons.

Have I been Counterdetected?
This should be the first thought on your mind. For all you know, this sub (if it is a sub) has been tracking you for the last 10 minutes. How can you tell? For starters, what was the last thing you did before you saw the signal? Were you slowly patrolling ahead? Did you move across the layer? Dip your TA under the layer? Change course? Come around the side of a seamount? If the detection occurred because you moved someplace, and in that new place detection was immediate, chances are very high that you both well inside detection range of each other and that counterdection has occurred. On the other hand, if this was a course or depth change made at a short interval, or if contact occurred while you were going slow and straight, then your opponent is probably just barely inside your detection range, which means if your opponent is faster than you counterdetection has probably not yet occurred.

As you track the target, you’ll get a better idea if you’ve been counterdetected. A speed estimate is helpful; if the contact is faster than you, you probably heard him/her first (and vice versa). Once you get a course estimate, you’ll be able to see if it’s possible that you are in a sonar blind spot. Note if the contact is moving in a straight line or making course changes. A straight line suggests he’s oblivious. So do course changes if they are back and forth along the same overall direction of advance. Course changes greater than 60 degrees away from the direction the target was moving suggest that he/she is tracking you (especially when using manual TMA). If the contact follows you across the layer, that’s also a pretty good sign you’ve been counterdetected.

If you have not been counterdetected, great—try to keep it that way. Maintain a low speed. Move toward a sonar blind spot. If the target is below the layer, get above—while leaving your TA below.

If you have been counterdetected, then your priority is obviously no longer preventing counterdetection, but preventing a solution. Accelerate to tactical speed (the highest speed you can move at before washout sets in) and make frequent, unpredictable course changes. For noisier subs with relatively high tactical speeds, such as the 688I and the Akula II’s with the Pelamida II, it may be advantageous to go to something less than full tactical speed to prevent giving away a DEMON contact—this is usually only a risk in favorable acoustic environments from relatively close range (e.g. if you got within detection range below the layer in a surface duct SSP but are now in the duct, tactical speed might cause a DEMON contact).

Do I have the right contact?
Fortunately, enemy subs are fairly easy to identify in most situations. You will not need (nor will you be able) to get a positive, 4 or 5 line narrowband classification. The main giveaway of a sub is how quiet it is. Surface ships that share the same first few lines with subs will be much louder than the sub at the same range and speed. The exception is the fishing boat, which at low speeds does have a rather low SL.

DEMON information also provides a dead giveaway against subs. Nearly all surface ships generate 3-4 line DEMON profiles (exceptions include the freighter and yacht), while subs generate 6-7 line profiles. The lines generated by a sub will be light and narrow, while a surface ship’s will be wide and bright. Also, most civilian ships do not change speed all that frequently.

This scenario assumes there are no other combatants in the area, so the only subsurface contact will be the enemy sub. You’ll know a contact is subsurface for sure if it is below the layer or if you can’t spot it on the periscope within about 10nm (less at night, in rain). Most surface vessels use active radar, so no ESM within about 15nm is also a strong sign that it is submerged. Radar use is an option, but its usefulness does not extend far beyond this hypothetical scenario for obvious reasons.

Finally, all of the hints for counterdetection are also evidence that the contact is the enemy sub.

Localization
For manual TMA tips, see the TACMAN (http://www.commanders-academy.com/forum/attachment.php?attachmentid=22&d=1134063508) or similar guides.

If aTMA is enabled, the solution is going to have some built-in error that gets smaller with time. If the target changes course or speed, error is re-introduced. Your course changes will also cause the solution to “loosen up” a bit at first, but once it “tightens up” again it will be a bit better than it would be if you had just moved in a straight line. aTMA does not do any better or worse do to lag or lead legs.

The best way to recognize if an aTMA solution is accurate is to look for the “steady state.” The error will tend to bounce around the real location, and will settle down at the real location over time. Enable “show history” for the contact to see the previous solutions.

When Should I Shoot?
Ideally, you should fire at the exact moment when the quality of your solution on your opponent is most superior (or least inferior) to your opponent’s solution on you—at the time of greatest advantage or least disadvantage. This is because the firing of a weapon moves both of you into the final sprint of the race. The quality of the solutions determines how far each of you has to sprint to the finish line. The better your solution at the time you shoot, the quicker you can get the weapon on the target. Your goal is to make sure you have the best starting position relative to your opponent before the sprint begins.

The concept that determines how much time you should spend tracking is marginal utility. If you’re using aTMA, the initial solution has a large amount of error, but will quickly begin to firm up. During this time, the marginal utility of time is very high, so you should use that time. But, once the solution bounces around a few times and begins to settle, the marginal utility of time begins to decrease.

With manual TMA the marginal utility of time is highest immediately after (the TA straightens out after) a course change. The first two lines on a new course help eliminate most incorrect solutions. Each additional line, however, will eliminate fewer solutions the one before it. Also, each additional TMA leg after the 2nd will eliminate fewer solutions than the leg before it.

Whenever your marginal utility of time is higher than your opponent’s, you are improving your position; whenever it is lower, you are worsening your position. With this concept in mind, here are two (three, sort of) possible starting situations.

Situation 1: You are tracking your opponent, opponent is not tracking you.
If you have not been counterdetected, then your opponent is not improving his/her solution. You can improve your solution without any cost. This situation will not last long. Take the shot as soon as it’s clear that your solution isn’t going to get significantly better.

Situation 2: You and your opponent are tracking each other.
If you have been counterdetected, do not take your time. Every minute you spend improving your solution is another minute your opponent does the same. If you detected your opponent first, you need to preserve your advantage; if you detected your opponent second, you need to try to catch up.

As discussed above, the marginal utility of time during tracking is very frontloaded, and peaks while the aTMA solution is firming up or early in the 2nd leg for a manual solution. To preserve an advantage, you need to fire as soon as possible after that peak. Any time after that, your opponent’s solution is improving more quickly than yours is and you are losing your advantage. Conversely, if you are at a disadvantage, then it is in your interest to prolong the process by holding your fire. Any time after the peak utility early on in the process, your marginal utility is higher than your opponent’s and you are catching up.

Situation 3: You have been fired upon
This isn’t really a situation where you choose when to fire. That decision has already been made for you. The starting blocks are wherever they are. Your opponent has already begun running (and probably started well ahead of you, else he/she wouldn’t have started the sprint). The race ends when one of player’s torpedoes hits the other’s sub, and you’re not going to win that race by keeping the torpedoes in the tube….

[Molon Labe]

Engagement Phase
Both of you now have weapons in the water (or maybe in the air). Your task now is to continue to track the target so that you can resteer or fire followup salvoes as necessary until weapon impact.
Weapon employment tactics (http://www.commanders-academy.com/forum/showthread.php?t=63) and torpedo evasion tactics (http://www.commanders-academy.com/forum/showthread.php?t=47) are already discussed in detail in other threads. What we’re mainly concerned about here is balancing those two goals.

Evasion

Getting away from the torpedoes. The torpedo evasion thread (http://www.commanders-academy.com/forum/showthread.php?t=47) is mostly about defeating a torpedo. Here, we expand the focus. It isn’t good enough to evade a torpedo, because that torpedo and others are being resteered at you after any failed attack. And there will be followup shots, especially if SUBROCs are being used. So the big-picture goal of evasion is to buy yourself time—enough time so that your weapons hit the enemy first, thus eliminating the threat of resteers and additional salvoes.

One obvious way to give yourself more time is to run from the torpedoes (“dragging”). Dragging forces the torpedoes to travel a longer distance and take more time doing so. You may be able to extend that distance beyond the torpedoes’ maximum range, forcing your opponent to fire again. The effectiveness of dragging is maximized when you are at maximum speed heading directly away from the weapon. However, in this state, you are not receiving any information about the enemy sub’s position and you are making his/her TMA very easy. So, if the torpedoes were fired from far enough inside no-escape range (http://www.commanders-academy.com/forum/attachment.php?attachmentid=136&d=1190658378)to make up for any time lost due to snaking, the drag will fail to outrange the torpedoes and you will not be able to get your weapons on target during the drag, so you will lose. But, if you’re confident you can outrange the torpedoes, then a pure drag can be reasonable if you’re willing to sacrifice your own offensive capability.

In most situations, you will want to drag at an angle to complicate your opponent’s TMA solution, while frequently slowing to tactical speed to get updates on your opponent’s (and the torpedoes’) position. You should use those updates to adjust your course to drag away from any torpedoes that have been steered onto a lead pursuit intercept with your present course. UUVs are also very helpful in tracking torpedoes

Foiling your opponent’s solution
Any time a torpedo spends at a course that is not a lead pursuit intercept course causes the intercept to take longer. If your opponent doesn’t know where you are, he/she will have to search the area of uncertainty with the torpedoes. At a minimum, this will cause lost time due to the weapons snaking. It may also put the weapons on a pure pursuit intercept course instead of lead pursuit, or may cause him/her to steer the weapons in the wrong direction altogether.

The best way to compromise a solution is to deny your opponent additional data. The best way to do this is to have an effective offense, which forces your opponent to accelerate above washout speed. In poor acoustic conditions (this includes being below the layer in a surface duct SSP), you may also be able to break contact altogether. Change sides of the layer frequently to reduce the chance that your opponent is listening on the right side when at tactical speed. Get behind terrain when available.

When it isn’t possible or advantageous to deny contact, your next best defense is maneuvering. Any course or speed change will introduce error to aTMA, at least for a time. Against manual TMA, every course or speed change creates potential incorrect solutions. Being on a lead LOS creates more incorrect solutions than being on lag. But, a lag LOS will move you away from your last known bearing faster, which may be advantageous if your opponent did not get a good solution to start with.

You should strive to maintain maximum speed as much as possible. The faster you are going, the faster you get away from the position you were in when your opponent had a good solution.

Keeping your weapons on target
Once the shooting begins, immediately mark your best solution on the map, along with the area of uncertainty. Mark the time as well. This is probably going to be the best data you have throughout the whole process; your opponent can only get so far from the location he/she started at.

Get as much information as possible. Make an immediate effort to use your enemy’s increased SL to get DEMON and additional sonar array contacts. Knowing your opponent’s speed during evasion will be very helpful in eliminating erroneous solutions, and it will tell you when he/she is listening and when he/she is running. Getting a master contact will tighten your range solution significantly.

Slow down whenever you can afford to to get more data (but accelerate ASAP once you get that data). Try to time these around the even-numbered minutes on the clock so you get a new line at TMA. Even when you aren’t getting a line at TMA, locate the contact’s bearing on the sonar and make a note of it. Even without a range and course solution, bearing data is sufficient to resteer your weapons onto a pure pursuit intercept course.

If you’re using manual TMA, update your solution during sprints. Use your knowledge of the enemy sub’s starting point to make reasonable guesses about his/her evasion course. If you have solid bearing and DEMON data, you can maintain a high quality solution though several course changes. Even if you don’t have DEMON data, you can make an educated guess about your opponent’s speed based on the maximum and tactical speeds of the sub.

It’s a good idea to keep a UUV out. Direct contact with the sub is still unlikely, but, if the sub fires again you might get an instant triangulation of the launch point between the UUV line and the TIW alert bearing.

You should be constantly resteering your weapons to maintain a lead pursuit course on the enemy sub. Once your weapons are far enough out that they might be in the area the sub is in, it’s time to start enabling them. (Or, if they enabled before they reached that area, you should pre-enable them). Upon any acquisition, note the new course of the torpedo and the bearing of the target. If the torpedo course is not in the direction of the bearing line, then you know for a fact it isn’t on the right target and need to pre-enable it. Do mark the suspected location of that object though, because it is a rather obvious “sub was here” signpost which may help you find the target. Multiple decoys essentially amount to a trail of breadcrumbs for your weapons to follow and for you to use to confirm your TMA solution.

If the torpedo is headed in the right direction, let it run, but set a course for it to follow should it turn out to be locked onto a decoy. It is very easy to get a torpedo to chase a decoy, but it is much harder for your enemy to prevent reacquisition on the other side if you’ve told the torpedo what to do when it passes the decoy. Don’t forget to resteer any additional weapons based upon acquisition info, whether from the real target or from decoys.

Balancing Offense and Defense
Your opponent’s accuracy is going to determine how defensive you need to be. If there are torpedoes nearby on lead pursuit and SUBROCs splashing down around you, evasion has to take the highest priority. On the other side of the scale, if there is nothing threatening you anytime soon then you can stay at tactical speed and track your opponent’s every move.

The potency of your opponent’s offense is determined by the quality of his/her solution and how quickly he/she can get a weapon out to your position. There are three main ways to judge the quality of your opponent’s solution.

The first is by tracking the incoming torpedoes. For wireguided torps, note how quickly they are steered back to lead pursuit after a course change. Quick responses mean good solutions. Slow responses, or better yet, reliance on a spread that is not resteered, indicate a poor solution. Similarly, if SUBROCs are splashing down very close, the solution is probably good, in particular if they are splashing down close by and on different bearings. On the other hand, far-off shots indicate your opponent is clueless, and a range-spread pattern suggests he/she has bearing information, but no range solution.

The second is by noting the position the torpedoes enable in. Early enabling suggests your opponent has a poor range solution. Delayed enabling is a sign of that your opponent is confident with his/her solution (although it’s possible that confidence is misplaced—right, Captain Tupolev?)

Finally, in particular if you have solid DEMON data, your own tracking of the target will tell you a lot about how much of a priority maintaining a solution has been for your opponent. If he/she has never slowed down, isn’t following you across the layer, is maintaining a lead LOS (manual TMA matches only), has been evading in a straight line (manual TMA matches only) or is firing a lot of weapons (trying to use the torpedoes’ sonar instead of the sub’s), it’s a good bet that your opponent’s solution isn’t as good as it could be.

[Molon Labe]

Parting Thoughts
The best defense is a good offense. A sub’s ability to target you is severely compromised when it is forced defensive, and once destroyed, any remaining weapons are usually easy to evade. This underscores the importance of getting ahead early. The sub that is first to detect the other will usually be the only one to get a good solution. Once the now-offensive sub has a good solution, he/she will fire before the now-defensive sub can get a solution. Armed with the knowledge of the defensive sub’s position at the start of evasion, the offensive sub maintains a quality solution during the engagement and gets torpedoes on target quickly. Meanwhile, the defending sub, knowing only the bearing of the offensive sub, has to enable torpedoes all along the bearing line. The offensive submarine’s torpedoes get close more quickly, which forces the defensive sub to become more defensive, causing it to completely lose track of the offensive sub. The defensive sub may manage to decoy a torpedo, but the offensive sub sees this happen and just turns it around, getting the kill a few seconds later.


For manual TMA matches, the sub getting first detection has about 2 to 1 odds of winning. aTMA evens things out a lot because its solutions are generated from truth data rather than any sort of geometric analysis. It tends to erase an advantage one player has gained. Still, the sub with the first detection still has better than 50-50 odds.

Further Reading: Differential Submarine ASW Tactics (http://www.commanders-academy.com/forum/showthread.php?t=21734)
Related Topics:
Active Sonar use (http://www.commanders-academy.com/forum/showthread.php?t=152)
UUVs. (http://www.commanders-academy.com/forum/showthread.php?t=100)
..and of course the weapons and evasion threads that have been linked about 3 times so far.