SONAR in the ship

[RF]

Hi, RF...

I apologise if this sounds stupid, but... I'm very fond of the movie "Das Boot" and would like to adress a particular detail in the movie that raise yet an interesting question, just since you mentioned the destroyer-use of sonars. In the movie, each time a destroyer closes in on U-96, you hear this kind of "Ping" getting more and more frequent as the distance closes. If I'm not mistaking, that sound give me a notion of an active sonar being used, not a passive listening device. :think:

By the way, was the British ASDIC a passive or active sonar device?

Best Regards

I believe the movie mentioned the use of ultra-sonics, an active sonar device.

[RF]

Destroyer hull mounted sonar is relatively useless at high speed. 5-10 kts is an effective speed. This was true in the 70s so I'm sure it was true in the 40s as well.

How does it work then in a depth-charge run when the destroyer is going at 15-20 knots or so and to obtain the simultaneous echo to know when to drop the charges?

[Terje Langoy]

It gets phsycological, as they say. Had the sonar alone been completely accurate in position, depth and bearing, no sub would be able to escape, would it? My guess is that the sonar was just a supportive device that along with map plots would give them the estimated postion, depth and heading of the sub. The sonar provided a probable depth and the map plots a probable heading. From there, it was a game of cat & mouse. But that's just a wild guess that seems logical to me. As for the speed, it makes pretty good sense that the destroyers made 15-20 knots during a depth charge run. Not because the sonar was efficent at this speed but because the destroyer would be more vulnerable to a torpedo attack doing only 5-10 knots. Whether this is the case, I'm not sure, but that's what I'm able to deduce from my point of view.

Regards

[tommy303]

Doing a sonar search for a suspected submarine would probably be done at 5 to ten knots, and once a contact was made, and the target was being tracked by the sonar, it was possible to make a depth charge attack at 15 or so knots, or a little more depending on sea state. Enemy bearing was fairly accurately assessed by the sonar or ASDIC, as was range; depth was determined as range closed and the sonar beam narrowed, using a triangulation formula. In WW2 installations the sonar head could be turned, but the sound beam was more or less fixed at a downward angle. As the destroyer drew closer to the target, submarine would eventually disappear off the scope, and the point at which this occurred was used to give an accurate final depth reading for last minute adjustment of the depth charge settings.

The last few hundred yards were essentially a blind run, with the depth charges being released on signal from a timer. In this critical time the sub could alter course to evade the pattern or go deeper or shallower, which is what made it difficult to actually score a kill. This blind run in was one reason ahead throwing weapons such as Hedgehog became increasingly important, as they could be fired when the sub was still on the scope.

After the run the destroyer would have to relocate the target if possible once the water settled down after the depth charge explosions, and begin the whole process of reaquiring the target and getting ready for the next attack. If there was more than one destroyer, it was possible for one to hold the other on sonar while its companion attacked, allowing successive attacks at much shorter intervals. It also made it more difficult for a sub to evade an attack, as the one destroyer could help direct the other.

[Bgile]

Tommy pretty much nailed it down.

Ideally there are two or more destroyers in the attack, one tracking the target submarine while the other one attacks.

[wadinga]

All,
The Bismarck thread has a splendid launch picture which doesn't show the 60 holes per side GHG passive sonar installation Bismarck was supposed to have below the waterline near Bruno turret.

If Bill Jurens or another marine engineer is about, I would be interested to hear when these hull penetrations would have been installed, after launch seems a bit late. I realize one might want to keep them secret, but each hole seems to have been about 3cm in diameter, so I presume it would have been difficult to do during the fitting-out phase.

All the Best
Wadinga

[tommy303]

The microphones could have been installed during building prior to launch, in which case it is possible a censor airbrushed them out, or they may have been installed during fitting out when the ship was dry docked. Prinz Eugen had them too, although like Bismarck one does not see them at launch, so again it might have been something censors dealt with on photos released for publication.

[dunmunro]

Hi, RF...

I apologise if this sounds stupid, but... I'm very fond of the movie "Das Boot" and would like to adress a particular detail in the movie that raise yet an interesting question, just since you mentioned the destroyer-use of sonars. In the movie, each time a destroyer closes in on U-96, you hear this kind of "Ping" getting more and more frequent as the distance closes. If I'm not mistaking, that sound give me a notion of an active sonar being used, not a passive listening device.

By the way, was the British ASDIC a passive or active sonar device?

Best Regards

I would suggest that you try and watch the movie, "The Cruel Sea" which gives a very nice overview of the use of Asdic, and is a good view of the U-boat war, from the allied side.

[Dave Saxton]

On Oct 10th 1940 the calibration and test kits SPP were ordered for the Bismarck, Gneisenau, Scharnhorst, Tirpitz, Hipper, and a ship to be named Seydlitz. This kit was already in use on the Prinz Eugen. This kit was used exclusively with the S-Gerate or active sonar; proving the installation (or planned installation) of S-Gerate sonars on those warships.

The S-Gerate was tested on the Prinz in Aug 1940. It showed a capability to accurately measure range even at relatively high cruising speeds, and an intial directional accuracy within 4*. The active Sonar was continiuously improved throughout 1941 and by 1942 could boast the following features:

*The console GH with visual indicators for range and fine range within 300 meters, synchronizing two or more S-Gerate sets

* A audio indicator that allowed the operator to distinguish between moving and static targets based on doppler

* A doppler tachometer that measured relative speed to within 1 knot.

* A pulse generator of 5 kw (adjustable from 25 watts to 5 kw) that was very small and compact.

*A special compact duplexing transducer for the bow bulb of large warships.

* A duplexing circut to protect the recieving circut during active pulse operation.

*A control console with CRT and electrical time base

* A twin amplifier (reciever) with a heterodyne twin, with gain as function of range.

The construction was modular.

Direction could not be determined from a single pulse. It took several pulses so that the the sum/difference amplfiers could fix the direction of the target.

[Bgile]

Obviously any ship which is attempting to remain hidden won't go around transmitting on an active sonar. Destroyers used them in convoy because the convoy was making so much noise that the additional noise of the sonar transmitter was irrelevant, and U-boats were quiet enough that they weren't likely to pick one up passively anyway.

[hellomartin]

Gruppenhorchgerat......

http://www.bismarck-class.dk/technicall ... g/ghg.html

[wadinga]

Hello Hellomartin,

We have had a long, and at times terse, argument on the Danish site about the immense influence of the GHG on PG's actions at the Denmark Straits, (and Lutjen's) and whether Bismarck had a GHG at all, and their webmaster produced this drawing, but oddly refused to be drawn on what evidence it was based. It appears strangely, unnecessarily compact, when a bigger baseline would surely have made it more effective.

I have been searching for years for a photo or original drawing of this highly secret system on a surface ship but have found nothing. Amazing performance is claimed for this system (equalling modern systems), and yet at other times it seems to have been completely ineffectual. Ulrich has turned up interesting comments in the Tirpitz War Diary about GHG and the ideal listening speed.

To Tommy. Yes I guess censors might have airbrushed it out, but this was a public occasion in peacetime with foreign reporters around so it couldn't be hidden that easily. Usually censors just scraped off the emulsion or scratched the negative (no Paintshop then).

Dry docking after launch. Bismarck was drydocked in late June early July 1940 and maybe it was fitted then but viewing http://www.kbismarck.com/construci.html the alongside shot shows a strange block shaped structure attached to the hull in about the right location. Could this be a cofferdam stretching down below the waterline and allowing the installers to cut 60 holes (each side) in the hull to install GHG transducers? Does anybody know of any dry dock pictures which might show the system?

Dave, Glad to see you on the case. I have found the Bauer article but do you have more specifically on GHG? U-boats all had GHG and yet were apparently forced to use the MK1 eyeball to find convoys instead of this wonder system hearing many thrashing screws from many miles away.

http://www.prinzeugen.org/PG/BOOK/PRINZE.HTM describes with teutonic pride the trials where PG dodged 34 practice torpedoes off Balboa but totally fails to mention the follow up when the system was removed to be installed in USS Flying Fish. This is odd considering the author mentions the dismissive attitude of US technicians to PG's radar systems.

Hope others find this system as interesting as I do.

All the Best
wadinga

[Dave Saxton]

Hi Wadinga

In mid 1941 most sonar equipment was removed from U-boats because of space concerns. To what extent this termination included passive GHG sets is not known.

I have a book with a photo of the S-Gerate master controll console, or the GH, but no clear details of it's operation.

The distinctions between passive sonars (GHG) and active sonars (S-Gerate) is not at all clear. The passive sonars may have been the passive elements of the larger overall system. Much needs to be learned here and the available literature does not cover this well at all. Since the constructions were modular in nature, individual modules could be added or subtracted as needed. Each module was attached or detached in the same way as the GEMA radar modules; with no cabling between sub-modules, but a self attchment into a self contained, water proof, and shock resistant rack mountiing.

In mid 1939 there were 19 sonar systems in service on various vessels and a few U-boats. In Aug 1939 the original S-Gerate design was superceded by a new type called the Type-200. The performance was radically improved, but it was a progression throughout 1940 and 1941 to reach the latter performance standards. During this period more compact sonar sysyems were developed for possible U-boat use, but I don't know if these were ever installed in U-boats.

At the close of 1941 there were 250 total sonar systems delivered, but I don't know how this breaks down into specifics.

AEG developed a competing sonar system that was more compact during the later stages of the war, but I don't know the extent of it's usage, or many details about it.

[tommy303]

Hi Wadinga,

Paul Schmalenbach described the arrangement on Prinz Eugen as being a horseshoe shape installation, and Whitley in his book on destroyers mentions that other configurations had been tried on the light cruisers as experiments, but discarded. A similar trial and error process seems to have been used on Uboats as well. It would appear that the horseshoe, was the one the Germans eventually adopted as the best, even on Uboats, until the Balkangeraet at least.

I have also searched photos, and still am, but the are elusive--either too small or too dark so far. I will let you know, though if I find one.

[hellomartin]

Hi Wadinga/Dave,

I am relatively new here and I am wondering if anyone connected with this site has made contact with Blohm and Voss? I visited the shipyard in Hamburg a couple of years ago and saw the official ship-builders model. Amazingly, there are actually off-cuts of Bismarck still lying around in the yard.

I have got stuck into a couple of debates on the site about various esoteric aspects of the ship....the latest being the rationale behind the domed covers on two of the search lights. I guess the attraction is in being some kind of historic detective and also understanding more about the ultimate fighting machine. However, I must assume there are people around at the ship yard who have access proper information on many of these issues.

Presumably a German would be best positioned to make contact, if someone has not done already?

Any thoughts?

Martin