Resting on the bottom for a few hours..

[JamesT73J]

Playing SH3 + GWX Gold and have dropped into the Med for a quick look at Gibraltar, late 1940. Got within a couple of km's of the port in absolutely foul weather at night; lots of traffic and escorts. My plan was to lie on the bottom overnight in about 70m of water, and have a peek through the periscope in the morning, then surface in the evening and sink some stuff.

Bottoming out was easy enough, but after after about 6 hours an escort passed nearby and pinged me, and of course utterly trashed my sub once the charges came.

I'm curious how I was detected. I realised too late that although I was at full stop, I hadn't chosen silent running. Is there enough noise from a submerged, still sub to allow passive sensor detection in SH3?

Cheers

James

[Submarine]

Water is one of the best transmitters of sound, and there are stories of ships picking up u-boat crew members talking and that is all they need. So without silent running, you are always screwed :salute:

[ryanglavin]

If you don't have silent running on (theoretically, you can't really prove this), the crew could still make all the noise and eat and walk around as much as they want.

[Lord Biceps]

The game doesn't appear to recognize landforms in any other sense than that they can't be navigated through. In other words, the ship pinging you only finds your sub, not the land you're resting on, as if your sub had been floating freely in the water.

You can also spot ships (and be spotted) through land. This caused quite a bit of trouble for me at Scapa Flow recently, as I was being bombarded by warships from several directions while being completely sheltered (or so I thought) by surrounding islands and coastlines, and not being able to even visually locate where the shots were coming from.

This is a major annoyance for me, I hope they'll fix it in SH5 (or did they do that in SH4? I haven't played it yet). :down:

[GoldenRivet]

(or did they do that in SH4? I haven't played it yet). :down:

this was not fixed in SH4





I wouldnt hold my breath awaiting the correction to arrive in SH5 either

[krashkart]

Hrm, good stuff to know. Accidentally engaged a destroyer (*cough* The game cheated, I swear!) and had to dive in a hurry. Very glad I remembered the silent running mode, I think it helped spare the sub and crew. Took a good thumping from the ashcans but was able to slip away. Just glad their gunners had bad aim. :o

[Frank0001]

I'm curious how I was detected. I realised too late that although I was at full stop, I hadn't chosen silent running. Is there enough noise from a submerged, still sub to allow passive sensor detection in SH3?

Odd really, that must mean the escorts are always listening/pinging, even when without suspicion?

[JamesT73J]

I don't think the idea of a coastal ASW vessel being on constant sonar watch that strange; it's probably a standing order; I know they certainly were when on escort duty. It must be hard work with such a shallow environment with lots of traffic. Anyone try SH1? Coastal DD's used to ping constantly, and they usually detected you.

I'm going to replay later trying the silent running method. If I'm detected passively I can only assume that there is some noise emission even on silent running.

I come from SC / DW with the knowledge that all platforms emit noise all the time, to some extent, so it's merely a matter of the emitter being close enough to the listener before detection occurs; it was therefore highly unlikely that one could close on a vessel with listening gear unless acoustic conditions were very very bad.

[Frank0001]

I've had a few times where I'd wait on course of a fat convoy, silent running and engines off. The escorts would still pick me up if they're close enough.
Sometimes they just sail happily by.

[GREY WOLF 3]

Astic is A system using transmitted and reflected underwater sound waves to detect and locate submerged objects or measure the distance to the floor of a body of water. So with no sound at all it picks up THAT BIG MASS of metal in your case a sub.

[Jimbuna]

You need the cloaking device mod otherwise there is no way of hiding your presence.

Stoooopid game engine http://www.psionguild.org/forums/images/smilies/wolfsmilies/wacko.gif

[Dave Kay]

this was not fixed in SH4





I wouldnt hold my breath awaiting the correction to arrive in SH5 either

Good thing you pointed that out GR, because I was just about to turn blue-in-the-face until I read further down and saw your post....:har::har::har::rotfl2::rotfl2::haha::haha ::haha::rotfl2::har::har::har:

[Torvald Von Mansee]

Odd really, that must mean the escorts are always listening/pinging, even when without suspicion?

Sigh...the RN and USN seem to always be on an artificially high level of alert. I don't think it's terribly realistic.

Of course, water as clear as a bell while sneaking into Loch Ewe is probably also not very realistic, either.

[Leandros]

Astic is A system using transmitted and reflected underwater sound waves to detect and locate submerged objects or measure the distance to the floor of a body of water. So with no sound at all it picks up THAT BIG MASS of metal in your case a sub.
But then you ought to hear the pinging. My experience is that, for a example a lead escort, only starts pinging after it has got suspicious about you.

[JamesT73J]

But then you ought to hear the pinging. My experience is that, for a example a lead escort, only starts pinging after it has got suspicious about you.


This is my experience. ASW units seem to listen passively, then locate using active sonar. I notice that silent running disables torpedo loading, pumps, the snort mast (if you have one); I suspect SH3 sums these things (along with your motor and screw noise) into an emissions total. There appears to be no particular penalty for having the pumps switched off; in AOD you couldn't do this for long periods as you'd start to sink as the bilge filled up.

I tried the scenario again, this time running very slowly and using silent running. I was able to stay in Gibraltar harbour for 24 hrs, with no bother.

Much as I adore GWX I wish the escorts weren't such good listeners, especially early war. You can't go flank underwater within 4km of an escort sometimes. Late-war this is completely understandable (there are many cases of u-boats detected ahead of convoys purely by passive means) but early on during the happy times they could do with some ear plugs.


J

[Jimbuna]

In the early war period there are fewer escorts with veteran and elite status which should dampen down the listening ability/effectiveness of some, but not all.

[ryanglavin]

I wish someone put the Seawolf Class sub in SH3 to be compatible with GWX 3.0...

Firing missiles while 20 miles away at a convoy would be hilarious...!

[G7eT2]

From what I have read convoy escorts and patrol vessels did ping the entire time they were on duty, regardless of whether they suspected anything.

Presumably the game does not model this because it would be incredibly annoying to have to listen to all the pinging anytime an asdic equipped vessel was close by.

So you may actually be being detected by asdic initially rather than hydrophone effect, and the game then starts up the pinging sound effect to add to the atmosphere of being hunted.

I could be wrong and will no doubt be made fully aware of the fact if I am. :)

[Jimbuna]

From what I have read convoy escorts and patrol vessels did ping the entire time they were on duty, regardless of whether they suspected anything.

Presumably the game does not model this because it would be incredibly annoying to have to listen to all the pinging anytime an asdic equipped vessel was close by.

So you may actually be being detected by asdic initially rather than hydrophone effect, and the game then starts up the pinging sound effect to add to the atmosphere of being hunted.

I could be wrong and will no doubt be made fully aware of the fact if I am. :)

What sources are you quoting from regarding the constant pinging?

My understanding is that escorts wouldn't go 'active' until they suspected there was a U-boat in their immediate vicinity.

Constant active pinging would simply forewarn a U-boat of an approaching convoy.

[ReFaN]

What sources are you quoting from regarding the constant pinging?

My understanding is that escorts wouldn't go 'active' until they suspected there was a U-boat in their immediate vicinity.

Constant active pinging would simply forewarn a U-boat of an approaching convoy.

in the Book *Iron coffins* the author stated that the Escorts pinged all the time, but that may just be a thing i read.

[G7eT2]

Alarm !

Noob Kaleun finds himself under scrutiny from nuclear powered, never sleeping uber veteran Jimbuna.:o

Quick, should I crashdive or abandon ship ?

No mustn't panic. Must attempt coherent argument.

OK here goes :

This link http://www.uboat.net/forums/read.php?20,63599,63678#msg-63678
is to a posting by a person who claims to have been a navigator/tactician on a frigate in Captain Walker's group, in which he refers to 24/7 pinging.

In this link http://jproc.ca/sari/asd_et1.html
the last paragraph describing the Type 23 seems to indicate constant use of asdic.
In addition the final paragraph on the page describes pausing from pinging to listen for incoming torpedoes.

I know that is not many references, and the more I try to look into this the less I seem to know and the more my head hurts.
Anyway it may be possible that with a convoy being detectable on hydrophone at as many as 100kms away the additional noise of active sonar is not such a big deal. It would be interesting to know how far away pings could be heard by the uboats. Also it must have been very difficult to distinguish the sound of a uboat rigged for silent running over the general loud noise of a convoy, which would make asdic a better option.

Regarding the pings, as I understand it the crew only heard the 'gravel thrown against the hull' sound ( never the Hunt for Red October style "ping" ) when caught in the beam of the early model asdic, and only the uboat's hydrophone operator could hear the later model asdic through his equipment.

Maybe.


Ps I do not mean to question the value of the movie Hunt for Red October as an historically accurate documentary.;)

[Jimbuna]

Alarm !

Noob Kaleun finds himself under scrutiny from nuclear powered, never sleeping uber veteran Jimbuna.:o

Quick, should I crashdive or abandon ship ?

No mustn't panic. Must attempt coherent argument.


LMAO :DL


This link http://www.uboat.net/forums/read.php...3678#msg-63678 (http://www.uboat.net/forums/read.php?20,63599,63678#msg-63678)
is to a posting by a person who claims to have been a navigator/tactician on a frigate in Captain Walker's group, in which he refers to 24/7 pinging.


You appear to be cherry picking sections of your own links.....why aren't you quoting the multiple texts and opinions on the same page that support the theory that passive sonar was commonly used EG:

They are reproduced here to prove that allied escorts did in fact use passive listening against the U-Boats (and that they could hear U-Boats on the surface runnig at high speed).


I posted this as there was a long debate a while ago on this forum as to weather or not the RN used passive means at all to track U-Boats. Evidence is that the RN relied primarily on active means to track U-Boats (the correct technique to gaurd a 'perimeter' with the technology available at the time). Various opinions were expressed that the RN rellied exclusively on active sonar and utterly ignored passive sonar, which was not the case, but i did not have the documentary evidence to hand to back up what i was saying.



I've never understood why there's any doubt about the use of passive sonar in WWII ASW, and only recently heard of people questioning it. Of course it was used.

Put it this way, one of the most famous concepts of submarine tactics is "silent running", which is only effective when escaping passive sonar. "Run Silent, Run Deep", and so on.

I've found documentary evidence for RN use of 'passive listening' during WW2 against U-Boats. The evidence comes from the Book "Black May" and in several accounts of escorts atatcking U-Boats mention is made of contacts being either aquired or held on H/E (Hydrophone Effect, RN terminology for passive listening). I don't have the book in front of me right now, but as soon as i can i'll post the exact passages from the text.



Now from your second link....http://jproc.ca/sari/asd_et1.html....and from the final paragraph your making a direct reference to...

Bob Welland, relates some personal experience with torpedo detection. "The Asdic operators were always alert for torpedoes, and it became more important when the Germans introduced an electrically propelled model known as 'Gnat'. Its propeller noise could be heard out to a mile and the Asdic was efficient at picking it up. I always had the operator do a 360 degree listening sweep every few minutes. This sweep, with no pinging, only took about ten seconds to execute. During Haida's last convoy run to Russia, this procedure proved itself. We dodged two torpedoes, having had time to turn the ship into the Asdic detected rush-noise." After the HSD reported that the torpedoes had passed, we went on to attack the U-boat."

The above is a direct reference to passive detection.

Asdic in that period on surface ships relied heavily on decent weather conditions to enable it to have a semi decent range.

Have a look here for a better description:

http://www.uboat.net/articles/index.html?article=45


3.2. Technical description

The first practical sonar units have been constructed between WW1 and WW2. The best working frequency was 20 kHz, pulse power was 50 W. Range was 1000 to 1500 metres (good working conditions) or 500 to 700 metres (bad working conditions). In WW2 there are two types of sonar, projection type and panoramic type.
Projection sonar: beam 5 to 15 degrees, frequency 10 to 50 kHz, output pulse power 50 to 200 W, duration of signal 30 to 200 ms. Range was 800 to 4500 metres. In winter range was better than in summer. In WW2 average range of submarine detecting was 1350 metres (from a destroyer).


If a U-boat got within active range it was probably already too late because it would have more than likely launched its attack.

On the other hand if a U-boat was picked up on passive detection (listening range is longer than active range) an escort would race down the bearing and go 'active' when nearer for a more positive 'fix'.

Here is another link on the disparity in systems ranges:

http://www.uboat.net/articles/id/52



When detected (submerged) submarine stopped her moving, the operator was able to determine which mechanisms of the submarine still operated. To avoid own noises, a submarine could use underwater sound detector if her speed was up to 6 knots. If a submarine speed was 4 knots, the submarine's underwater sound detector average distance of detecting another object was: - for a destroyer- 5 to 10 nautical miles,
- for a cargo ship- 3.5 to 7.5 nautical miles,
- for a convoy- up to 50 nautical miles. If a submarine speed was 15 knots, the submarine's underwater sound detector possibility of detecting another object was rapidly decreased [although no submarines except XXI and XXIII were able to reach that speed during WWII]. In that case, average distance of detecting another object was up to few hundred metres.


Or to put it another way....a hydrophone (in the right conditions) could pick up the sounds of a convoy at ranges up to 50km so what would be the point of an escort going active with a signal that could only travel a few thousand yards (on a good day) and in so doing advertising its presence to a listening device that was far longer ranged?

[Torplexed]

I think the best analogy I ever read for active versus passive detection was one where you're a large, pitch-dark room full of people with guns trying to kill you. If you decide to switch on a flashlight you might spot one of them. However, at that moment they are all going to spot you. ;)

[G7eT2]

I knew I should have panicked.:damn:

Still my batteries are not dead yet so the battle continues...:stare:


My first post came from one of a series of threads, on the uboat.net Technology and Operations forum, initiated by someone called Phil Gollin. He was trying to argue that escorts used active sonar only (he was accused of trolling for this). I disagree as did everyone on the forum. That is why there are multiple entries on that page supporting the use of passive sonar by escorts.

My suggestion is that escorts used both passive and active sonar/asdic 24/7. In your first quote an average detection distance of a uboat of 1350 metres is given. I think that with enough escorts operating at 2-4 kms from the convoy with this detection range, it would be very difficult for a uboat to close to within their preferred firing range of less than 1000 m.

It also mentions Panoramic sonar available from 1943 with a range of up to 3000m in all directions simultaneously. That would really ruin a Kaleun's day.
Please don't bring this to GWX's attention.(Too late Jimbuna is GWX !:cry:)

With regard to the use of active sonar by escorts giving away the convoy's position :

-from the same page as your second quote -
6. Conclusion

In WW2 active sonar (Asdic) was fitted on a surface ships. It was so because the surface ships didn't care if submarines knew for their presence or not. Even better, presence of surface ship (a destroyer or a patrol craft, for example) caused giving up of submarine attack. Also, with the active sonar (Asdic) it was possible to determine range between the surface ship and submarine.

- further to your case from this link http://maritime.org/fleetsub/sonar/chap5.htm
Reporting enemy echo-ranging Sometimes a ship's pinging can be picked up before you can hear its screws. Any ship that is pinging is out searching for submarines. Merchant vessels are not equipped for echo-ranging.
(my underlining)

- further to my case from a few pages later in the same link http://maritime.org/fleetsub/sonar/chap6.htm
Why submarines do not echo-range continuously
Since the speed of surface escort ships produces a noise level too high for efficient listening, they depend heavily on echo-ranging to detect submarines. In fact, surface escorts echo-range continuously. But submarines hardly ever echo-range, because a submarine has to keep its location secret from the enemy. Continuous pinging would be a dead giveaway.



Torplexed - I agree totally with your analogy but think it refers more to subs than escorts.



Can I surface now ? :hmmm:

[utops]

Year ago i was watching on youtube old war movie about flower corvette and her crew.
When she escorting convoy, her asdic was on constantly. Rate of ping was low,but still on duty.

Maybe this bit of movie was based on facts. Dunno.

:06:

[BillCar]

LMAO :DL
Now from your second link....http://jproc.ca/sari/asd_et1.html....and from the final paragraph your making a direct reference to...



The above is a direct reference to passive detection.



My grandfather sailed on Haida as a radar gunner PO in the commissioning crew, 1943. Switched to the Huron in 1944, though, and so was not present for the event described above (if I recall correctly, Iroquois was almost hit by the same torpedoes).

Always cool to see references to some of his ships on Subsim!

PS: He sailed on two Flower class corvettes and two Tribal class destroyers in the RCN, and saw a ton of convoy duty. I'll be seeing him later this week when my family celebrates my brother's birthday, and will ask him about whether or not they were constantly pinging. He'll know, for certain. We can then put this to bed.

[Deputy]

I can't remember which book I read it in, but at the very end of the war a Type XXI was at sea and able to track and target a convoy with ease without being detected. They didn't fire because the war was over. But they did do a "just for the heck of it" simulated attack and it was quite successful. No detections whatsoever.

[Weisia]

I think I read it on one of the u-boat sites that destroyers patrolling along the british coast reguraly depth-charged ship wrecks sitting on the seafloor. This might suggest that 24/7 ping was enabeled.

About the type XXI sneaking undetected inside a convoy wikipedia says:
"A few hours after receiving the cease-fire order, U-2511 spotted a group of British warships. Korvettenkapitän Adalbert Schnee approached to within 500 meters of the British cruiser HMS Norfolk without being detected."

[Deputy]

I think I read it on one of the u-boat sites that destroyers patrolling along the british coast reguraly depth-charged ship wrecks sitting on the seafloor. This might suggest that 24/7 ping was enabeled.

About the type XXI sneaking undetected inside a convoy wikipedia says:
"A few hours after receiving the cease-fire order, U-2511 spotted a group of British warships. Korvettenkapitän Adalbert Schnee approached to within 500 meters of the British cruiser HMS Norfolk without being detected."

That was the sub, but it was written in much more detail in a book. Wish to heck I could remember which book it was, but the sub commander wrote the story and it was very detailed.

[Deputy]

I just wish I could rest on the bottom without getting a ton of damage to the sub. Is there some trick to doing it? I make sure the forward speed is zero and I still get all kinds of damage when I touch bottom.

[Panser]

I just wish I could rest on the bottom without getting a ton of damage to the sub. Is there some trick to doing it? I make sure the forward speed is zero and I still get all kinds of damage when I touch bottom.

Stock game behaviour is to damage the sub if it grounds, even in a controlled manner. Try the seabed repair mod for GWX 2.1. It seems to work fine for GWX3 too :)

http://www.subsim.com/radioroom/downloads.php?do=file&id=957

[Deputy]

Stock game behaviour is to damage the sub if it grounds, even in a controlled manner. Try the seabed repair mod for GWX 2.1. It seems to work fine for GWX3 too :)

http://www.subsim.com/radioroom/downloads.php?do=file&id=957


Thanks!! I'll give it a try. :up:

[Flopper]

Stock game behaviour is to damage the sub if it grounds, even in a controlled manner. Try the seabed repair mod for GWX 2.1. It seems to work fine for GWX3 too :)

http://www.subsim.com/radioroom/downloads.php?do=file&id=957

This has bugged the dog out of me for a while now, too. I'll give 'er a try, thanks!

[Threesixtyci]

Kinda pointless to bottom out the sub in SH3, though; unless, it's sinking or something. Seafloor in the game isn't recognized as a return. Your sub is the only object that gives a return echo and it's the same whether flying in the ocean or sitting at the bottom.

SH3 commander does add in a thermal layer at a random depth.... where surface sensors are weakened. That's about all we have, as far as magically disappearing from their sensors (other than the cone effect.). Only problem is... since it's random there no telling what that magic depth is. And if you like cruising on the Eastern side of Britain then... it's too shallow to ever reach the depth. Since the average depth is like 25 feet, there

[BillCar]

Forgot to ask my grandfather about this the other weekend, just stumbled into this thread again, so I figured I'd phone him. Having just gotten off the phone, I can confirm that yes, the escorts DID ping 24/7. This was standard procedure on all four ships my grandfather served on (two Flower class corvettes from 1940-1943 and two Tribal class destroyers from 1943-1945).

Pinging was done at a low but constant rate until an echo was caught by the operator, at which point the rate was increased in order to shorten the delay and help obtain precise fixes quickly.

Passive monitoring was also constant, and done in tandem with active ASDIC. Operators would switch out "every couple of hours" by my grandfather's reckoning, because the combination of pinging and intense listening was tiring. Generally speaking, you could expect to have two operators in the ASDIC hut at all times, with one listening and the other on standby. If action stations were sounded, you would have three operators on.

[Deputy]

I watched a really cool movie yesterday called "The Enemy Below" (Curt Jurgens and Robert Mitchum. If you can find it watch it!!) The German sub in the movie sat on the bottom and the American destroyer Escort lost them completely. According the the identification of the DE by the sub officers it was a Buckley class with the "most modern" anti-sub equipment. It wasn't until the sub lost patience and started up again that the DE was able to spot it again. Is this Hollywood or the truth? I know when playing 688i Attack Sub you can lose the enemy by using the thermal layers.

[Flopper]

I watched a really cool movie yesterday called "The Enemy Below" (Curt Jurgens and Robert Mitchum. If you can find it watch it!!) The German sub in the movie sat on the bottom and the American destroyer Escort lost them completely. According the the identification of the DE by the sub officers it was a Buckley class with the "most modern" anti-sub equipment. It wasn't until the sub lost patience and started up again that the DE was able to spot it again. Is this Hollywood or the truth? I know when playing 688i Attack Sub you can lose the enemy by using the thermal layers.

Amazingly, I saw this movie as a kid, and I remember Curt Jurgens giving the order, "the bottom!" I looked for this at blockbuster last weekend, but they didn't have it. I'd like to see it again, as I saw the trailer out on youtube recently.

[Deputy]

Amazingly, I saw this movie as a kid, and I remember Curt Jurgens giving the order, "the bottom!" I looked for this at blockbuster last weekend, but they didn't have it. I'd like to see it again, as I saw the trailer out on youtube recently.

I'd tell you where I got it but I'd get in deep poop with the mods and admin for even mentioning that source. :oops: The version I got has fantastic picture quality, is widescreen, and re-channeld for stereo. Before there was Das Boot, this was the BEST U-Boat movie ever released. :up:

[Panser]

Amazingly, I saw this movie as a kid, and I remember Curt Jurgens giving the order, "the bottom!" I looked for this at blockbuster last weekend, but they didn't have it. I'd like to see it again, as I saw the trailer out on youtube recently.

It's available quite cheap on amazon.co.uk, so i'm sure it would be available worldwide too :) The best part is you can support subsim if you go through the referrer on the subsim store page :DL

[BillCar]

I watched a really cool movie yesterday called "The Enemy Below" (Curt Jurgens and Robert Mitchum. If you can find it watch it!!) The German sub in the movie sat on the bottom and the American destroyer Escort lost them completely. According the the identification of the DE by the sub officers it was a Buckley class with the "most modern" anti-sub equipment. It wasn't until the sub lost patience and started up again that the DE was able to spot it again. Is this Hollywood or the truth? I know when playing 688i Attack Sub you can lose the enemy by using the thermal layers.

Yup, this could be done. Depended on a few factors, but it was done successfully right up to the end of WWII. I posted an after-action report from July of 1944 in another thread in which a duo of destroyers (one Canadian, one British) lost contact with a submarine when it went to the bottom of the English channel. It eventually surfaced and the Canadian destroyer put an HE round through the conning tower, starting a fire and causing the crew to abandon ship. Up until that part, though, they were doing pretty well!

[Deputy]

It's available quite cheap on amazon.co.uk, so i'm sure it would be available worldwide too :) The best part is you can support subsim if you go through the referrer on the subsim store page :DL

Probably a better idea than my way :up:

[Deputy]

Yup, this could be done. Depended on a few factors, but it was done successfully right up to the end of WWII. I posted an after-action report from July of 1944 in another thread in which a duo of destroyers (one Canadian, one British) lost contact with a submarine when it went to the bottom of the English channel. It eventually surfaced and the Canadian destroyer put an HE round through the conning tower, starting a fire and causing the crew to abandon ship. Up until that part, though, they were doing pretty well!

Unfortunately, it doesn't seem to be practical in SH3. :nope:

[BillCar]

Unfortunately, it doesn't seem to be practical in SH3. :nope:

Nope! :(

[Flopper]

Too bad resting on the bottom doesn't seem like a viable tactic. Also, it seems like the hydrophones would pick up active sonar from DDs a LONG way out.

[Panser]

I guess it has uses in the scope of the mod - for repairs without the danger of sinking.

If you wanted to lurk I suppose you could go silent running and then you would have a better chance of remaining undetected, particularly early in the war. Mostly I think such a tactic would be for roleplaying purposes or waiting for a surface ship to get bored and go away if you've been detected already.

[Sailor Steve]

Too bad resting on the bottom doesn't seem like a viable tactic. Also, it seems like the hydrophones would pick up active sonar from DDs a LONG way out.
It doesn't matter if the hydrophones pick up the sonar. Sure, it might lead you to a convoy, but it might also lead you to a hunter/killer group. And your hydrophones would likely pick up all the engine noise from the convoy anyway.

As for bottoming, it worked really well fifteen years ago in Aces Of The Deep. Most of the time you would lose them. Of course there was that little 'Getting stuck in the mud' problem.:dead:

[BillCar]

It doesn't matter if the hydrophones pick up the sonar. Sure, it might lead you to a convoy, but it might also lead you to a hunter/killer group. And your hydrophones would likely pick up all the engine noise from the convoy anyway.

Precisely. And you know that when you catch up to whatever it is, it's already going to be looking for you in a way that silent running alone can't overcome.

One other thing my grandfather mentioned on the phone was that they perceived active ASDIC as primary and passive as secondary. Granted, he was a radar operator (and later, radar gunnery specialist), but he had good friends working ASDIC on those ships, so I will take his word for it – it also jives with a lot of what I've been reading in the past few hours of researching it. They were always listening passively for screw sounds and other noises, of course, but the main point of interest to the operator was listening for echoes.