Thinking About Evading Searchers

[SeaQueen]

This morning I had a revelation, perhaps the best way to hide is not necessarily to be as slow and therefore quiet as possible. There's two competing processes involved in hiding. On the one hand, as you move more quickly, you are more easily detected at longer ranges. On the other hand, though, the effect of your motion is, in general, to frustrate the search plans of your opponent. That leads me to wonder, is there a best compromise between motion and silencing?

[PeriscopeDepth]

I think the main things that affect this are how far away you are from the searcher and how good his sensors are. Of course, it's also a function of how quiet you are. Surely when you think he won't hear you if you do 15 knots, it would be better to evade doing 15 rather than 5.

PD

[Kapitan]

I would hit 35 knots in viper if i was being chased by the FFG other than that like heck will i pass 15 knots unless evading a torp

[DS]

Searching for a submarine is like searching for a needle in a haystack. The faster the sub moves, the larger her noise signature, and therefore the larger a needle she is, making her that much easier to find. If we assume that a submarine stopped dead in the water has to be passed right over head to be heard (Needle), in a 100 square kilometers of ocean (haystack), it will take either a lot of time, or a lot of assets, before statisticaly you pass over the sub. If she is moving and creating a 2 square kilometer sound signature around her, she is statistically now much easier to find (much larger needle).

But then, I'm only a cyber-skipper. Maybe the BTDTs know somethign I don't.

[SeaQueen]

Now you're starting to think like I do. The thing is, she might be a larger needle to find, but she's also a moving needle which would be harder to find. One would expect that do one's best, there'd be a best compromise between being a moving needle and being slightly larger needle. I wonder where that compromise lies.

Searching for a submarine is like searching for a needle in a haystack. The faster the sub moves, the larger her noise signature, and therefore the larger a needle she is, making her that much easier to find. If we assume that a submarine stopped dead in the water has to be passed right over head to be heard (Needle), in a 100 square kilometers of ocean (haystack), it will take either a lot of time, or a lot of assets, before statisticaly you pass over the sub. If she is moving and creating a 2 square kilometer sound signature around her, she is statistically now much easier to find (much larger needle).

But then, I'm only a cyber-skipper. Maybe the BTDTs know somethign I don't.

[DS]

In thinking more about this, it might be more of an issue of moving into an area already searched rather than moving at a given speed. If you knew what areas had been searchd, and where the searchers were now, you could conceivably move into a pre-searcehd area and be safe for a while.

More realistically though, if you had no way of knowing what areas had already been searched, or what the size of the search area was to begin with, you are still faced with the same problem.

Still, there might be some mathematical probability formula that could be invoked to give one the best odds, but I have no idea how one would calculate that.

Cheers.

[SeaQueen]

More realistically though, if you had no way of knowing what areas had already been searched, or what the size of the search area was to begin with, you are still faced with the same problem.

Still, there might be some mathematical probability formula that could be invoked to give one the best odds, but I have no idea how one would calculate that.


I know what the probability of detection is as a function of time for a searcher moving randomly against a stationary target. In general, the effect of a target moving randomly is to take a searcher who has some kind of more organized search and turn it into a random search. It's easy to see that if you consider what the searcher's motion looks like in the reference frame of the target.

Huuum... I think I have something fun to play with at work today. :-)

[LoBlo]

Thing is that what if your searcher is faster than you are like helos and use active sonar.

Then the needle just got bigger and the hackstack smaller.:-?

[DS]

Let's look at it in this (admittedly simplistic) example.

Let us assume you have a 100 sq km search area, with one search asset that can scan a 1 sq km region at a time. I takes 5 minutes to complete the scan of 1sq km.

Let us also assume that when you are stationary, your noise signature gives a searcher a 50% chance of detecting you in the space of that 5 minutes before the searcher moves on. If you are moving, and thereby making more noise, the searcher has a 66% chance of detecting you.

With those constants, let's run the calcs:

If you stay still, you have a 0.5% chance of being detected on the 1st search grid. If you move from one grid to another, you have a 1.2% chance of being caught (66%/100 grid squares x 2 grid squares occupied during search phase 1).

If we assume this calc runs 100 times for the 100 squares searched one at a time, you have a 50% chance of being detected if you stay still, vs, a 120% (apparently statistically certain detection) chance of being detected if you kept moving.

Know, I am NOT a statistician, nor am I a real word tactician. Still, if you acknowledge your chances of detection are smaller the quieter you are, and you have no way of knowing if you are actually moving TOWARDS a searcher instead of away from one, it seems to me you are better off staying still. That said, in the real world, you almost always have some information, but never all information, so if I hear active sonar ranging to the south, I may choose to move away, even though I may be unwittingly moving towards a silent enemy in wait to the north.

[LoBlo]

Sure if no ones knows where to start looking... but in my game experience evading becomes important once you've launched that first salvo, then everyone knows almost *exactly* where you are and where to start looking. Your cover is blown because everyone has a clear datum to prosecute. 1-2 ASW aircraft are no doubt blazing at 100 knots to your exact location (if the AI is any good). If you say still too long, a active dipping sonar is about to drop right down on your head to ping you and a torp will soon follow. You have to move and move fast, because they are coming for ya and coming quickly at that.

Soo.....trying to slink away at 3-5 knots is suicide, you have to move fast to clear datum. After a strike your sleath is already blown, and location are already given away. Its just a matter of hoping that you have caused enough confusion to force the enemy to break contact for just an few minutes while you run for the hills.:yep:

[DS]

Yes, the assumption in that grid search scenario is that you started off hidden.

If we change the scenario to one where you want to hide from people who already have an good idea where you are (ie: along a certain line of bearing to a max range of x), then you can move as quickly away fro mthat line of bearing as quickly as you think you can without them generating a solution on your noise (they have current bearing, and may achieve general bearing drift and maybe even aproximate range, but try not to give up accurat range and course), then reduce noise and change course again (this time hopefully wrecking any budding fire solution they had been working on) and drift away quietly. This is essentially the manouver used to evade torpeodo launched at you that has not yet enabled - move off the bearing line, and out of the acquisition cone.

Of course, this pretty well goes out the window if the enemy is dropping sonobouys all over the area, or if you're getting nailed with active sonar as you manouver. In those cases, I think quiet, distance, and layers are probably your best bet.

[SeaQueen]

You're talking about evading a datum search, though. I'm thinking about area search, which is a little bit different. In that case, you're moving randomly and trying to avoid being seen by a searcher.

Usually players don't do this kind of evasion (huuum... I need to make a scenario where they do!), but it's important for scenario design. SSBNs are always hiding. SSGNs and SSNs conducting ASuW might lurk in an area avoiding searchers, until they're ready to strike a target.

Sure if no ones knows where to start looking... but in my game experience evading becomes important once you've launched that first salvo, then everyone knows almost *exactly* where you are and where to start looking.

[LoBlo]

Oh,

So what you mean is that if the enemy is using a systematic search, then staying in one spot would garantee that he will eventually run into you. But if your moving, then you will be moving into areas where the enemy has already searched, either forcing him to research previously searched areas, or fooling him all together.

Seem slike if the evading platform takes around the same tranist speed of the searching platforms he could probably minimize the chances of running into the enemy better as well, though I don't have any math to prove it, just a mental picture of icons moving around a map.

[Rip]

Man there are so many scenarios you have to say it depends. What is the subs mission. DO they have an idea where he is? Are there more or less likely places they are more likely to focus? Is there a target the ASW assets are protecting? AN area they are trying to keep the sub out of? You could go on at nauseum. Simply there are times when 10-15 knots is called for, there are times when <5kts are called for, and there are times to clear datum (run like hell away from the threat before slowing and turning to listen if you were followed). To can into as small an analysis as possible, if the area they are searching is big and they have no clue where you are go deep, slow, and stay very slow. If the area is small, they have a decent idea where you are, or are going try to keep up saome headway. If they know pretty damn close to where you are or have you in a small area.....clear datum. FOr instance if the ship broaches in real life or you think your masts were detected clearing datum is almost always prudent. Of course the game is a little stupid in some of these areas. But hell what do you want? Perfect realism?

:lurk:

[SeaQueen]

Oh,

So what you mean is that if the enemy is using a systematic search, then staying in one spot would garantee that he will eventually run into you. But if your moving, then you will be moving into areas where the enemy has already searched, either forcing him to research previously searched areas, or fooling him all together.


Exactly, I don't know if matching the searcher's speed is the best tactic, though. I imagine it would depend at least in part on the relative sizes of the areas being searched and the area covered by the searcher's sensor at your speed. So... I dunno... it's something interesting to think about.

[LoBlo]

I really don't know much about any RL search tatics.... no clue whatsoever actually. I've always assumed that the best search for a square area is a zig-zag sprinting and drifting to cover more ground.

Its probably something I should look more into, but heck I'm lazy.:p

[SeaQueen]

I really don't know much about any RL search tatics.... no clue whatsoever actually. I've always assumed that the best search for a square area is a zig-zag sprinting and drifting to cover more ground.

Its probably something I should look more into, but heck I'm lazy.:p

The mathematically "best" tactic depends on you knowing how far you can see with your sonar. That's part of why I always include the sonar range estimates given by the mission editor in the notes for ASW scenarios I make. It allows you to plan, make calculations, and estimates. The idea is to just choose a course that will cover the whole area eventually. The way to frustrate that, is for the target to move randomly. That ends up making your nice, orderly, optimal search look more like a random search.

In real life, (and usually in a simulation) other stuff manages to ruin your carefully planned search, so most searches (even planned ones) end up looking like random searches, even against stationary targets. That doens't mean your plan is necessarily a bad one, though. Personally, I like having a plan because it means I have to think less about things. ASW can get so cerebral so fast. I want as much as possible taken care of so that when the shooting starts, I don't have to worry about stuff that's not immediately important.

[LoBlo]

You know what I've always been curious about... whether the US Ohio SSBNs actually wander around in a organized patrol, or do they find a spot in the ocean and just sit and hover...

I've always thought that sitting and hovering were probably as good a strategy for not being found, but I guess the real answer really comes down to the orginal question you ask. Maybe they actually wander around the ocean in "systematic randomness" to decrease detection probabilities... there are probably only a handful of people in the world that actually know and ever will know.

[SeaQueen]

Just from the math, I think it's safe to infer that they probably move randomly in a fairly large box. I wouldn't be surprised if there was a computer program that somehow just generated pseudo random numbers and plotted a random course from that. Of course, the seed to the random number generator would be HIGHLY classified. I guess they could use the ship's clock, but then you could find them if you just picked the right algorithm and had a synchronized clock. I also wouldn't put it past them to just roll dice. It'd be simpler, that's for sure. I think in Blind Man's Bluff they said something about and baffles clearing.

You know what I've always been curious about... whether the US Ohio SSBNs actually wander around in a organized patrol, or do they find a spot in the ocean and just sit and hover...

I've always thought that sitting and hovering were probably as good a strategy for not being found, but I guess the real answer really comes down to the orginal question you ask. Maybe they actually wander around the ocean in "systematic randomness" to decrease detection probabilities... there are probably only a handful of people in the world that actually know and ever will know.