WiTP ASW Scen Design - Not RHS

[el cid again]

ORIGINAL: mikemike

This is slightly OT. I own a monograph about the German Type XXI subs. Their intended standard attack tactic was shooting at depth (100-200 feet I think) on target data obtained by an active sonar. The author remarks that "passive sonars of the time would not have been able to locate an active sonar", that is, they might have heard an active sonar operating, but could not have pinpointed its bearing or distance. I assume this was tested at the time, but can anybody confirm that this would have been so and explain why? On modern terms I know that a sub using active sonar is in effect shouting, "I'm here, kill me!". So what was different in WWII? Incompatible frequencies?

My understanding is the Type XXI were indeed intended to use submerged attacks - combining sonar data and homing torpedoes - but I have the impression they hoped to use passive sonar. Active sonar is a great way to say "I am here" - and everyone for many miles is going to hear it - without even a hydrophone - you can hear it everywhere (except in the air I suppose). And with a passive set one could at least get the direction of the active sonar. It would sort of defeat the XXI concept. But XXI was not a good design - it was a technical mistake not understood as such until long after the war. It is not clear it was controllable at speed - and nobody ever dared find out. The hull shape was wrong - was substantially rationalized during the war - and the Japanese guppy's were based on "superior hydrodynamic research" - but we were so sure the Germans must be better we just sank the Japanese boats without testing. It is possible this rushed - and improvised - design was not entirely integrated in other respects. [Type XXI was not designed as such - she was a modified Walther boat when the Walther engines prooved too far out - and ultimately the Walther concept prooved unfeasible. Few were built anywhere - and those build were such fire hazzards they boats - RN and Soviet - tore out those plants in favor of conventional ones. But the point is - a XXI was a hull designd for another purpose with the lower hull filled with batteries instead of tanks for peroxide - and the whole thing was an improvisation - never really perfected - dangerous at designed speed.] For good technical discussion in considerable detail see US Submarines Since World War Two (USNI, Friedman I think) - also see references to British training submarines using Walther engines (Conways, Janes, etc) and anything on the early Soviet "Type XXI variant" - a three shaft boat with Walther engines on the center shaft - which was disclosed by "senior Soviet naval officer" - a defector.

While sonar was put on submarines in several nations, it was common - probably normal - for a submarine only to have passive hydrophones - not active sonar. Submariners are reluctant to ping - gives away they are there. Often surface ships are confused by lots of things - and are never sure if there is a real sub around or not. Pings would erase a lot of the uncertainty of ASW.

[el cid again]

ORIGINAL: herwin

ORIGINAL: mikemike

This is slightly OT. I own a monograph about the German Type XXI subs. Their intended standard attack tactic was shooting at depth (100-200 feet I think) on target data obtained by an active sonar. The author remarks that "passive sonars of the time would not have been able to locate an active sonar", that is, they might have heard an active sonar operating, but could not have pinpointed its bearing or distance. I assume this was tested at the time, but can anybody confirm that this would have been so and explain why? On modern terms I know that a sub using active sonar is in effect shouting, "I'm here, kill me!". So what was different in WWII? Incompatible frequencies?

Distance--no. For that you need echo delay measurements or do TMA. Bearing--yes--if you got a long enough train of signals. Grossly speaking, you can localise a signal in azimuth just by comparing the intensity and timing in each ear, but for better than that in WWII you had to mechanically steer the receiver to point at the sound source. Post war, we started using sonar arrays, waterfall displays, and computers to identify the angle associated with the peak intensity.

We got the idea of arrays from the Germans - who used them. Big ones on surface ships - notably Prinz Eugen which we got as a prize and which we studied - becoming the basis of our later submarine sonars. Also small ones on submarines. Even German "hydrophones" were not primitive early models - but in a sense steerable arrays - although that meant you had to steer mechanically still - and there was no electronic display at all. They also used radar arrays - on submarines in particular.

[herwin]

ORIGINAL: el cid again

ORIGINAL: herwin

I'm sort of in agreement, but we do have the noise data--the USN data from WWII was declassified about thirty years ago.

But I am not aware that that data covered all possible submarines of all nations - and if it does not - we would have to guess for
a RTN, RNN, RN, name it class sub. And anyway - it is not very available - and Joe said we should be using standard reference data so
anyone with reasonable access to a library can confirm our data (when he supervised me on CHS work). If we honor the principle
of using generally available data - I don't think we can get there from here.

It's basically USN and German, but we have open source data available on a sample from other navies.

[mikemike]

ORIGINAL: el cid again

My understanding is the Type XXI were indeed intended to use submerged attacks - combining sonar data and homing torpedoes - but I have the impression they hoped to use passive sonar. Active sonar is a great way to say "I am here" - and everyone for many miles is going to hear it - without even a hydrophone - you can hear it everywhere (except in the air I suppose).

I've dug out the book and reread the relevant passage. The Type 21's were to be equipped with an active/passive sonar type SU, codenamed "Nibelung". This operated at 15 kHz with a peak impulse power of 400 watts and an impulse length of 20 milisecs. Being another piece of kit that was late, only part of the subs were equipped with it. It was built into the lower forward edge of the conning tower. Maximum range against big ships was 5-10 km depending on water conditions.

Attack tactics were developed in January, 1945 in exercises near Bornholm (a Danish island in the Baltic off the Swedish coast) using four submarines against a convoy consisting of thirteen ships. The preferred tactic was as follows: search for targets with the GHG (passive sonar array, range against single ships up to 20 km,aginst convoys up to 100 km under optimum conditions).Fix target bearing with the GHG. approach the target. When close enough, steer SU in passive mode to target bearing, get a bearing fix with the SU. Then switch to active and measure target distance by single "pings". Target range, course, and approximate speed could be obtained with a minimum of three "pings". These parameters would then be used to aim the torpedoes. The majority of torpedoes used would have been FAT pattern-running torpedoes, the T5 homing torpedoes were too slow, not optimized for use against merchant ships, and probably too expensive.

The author says that an attentive ASDIC operator could have detected the SU pulses, but would have been unable to locate the source of single "pings" due to the amplitude measuring method employed.

[JWE]

ORIGINAL: Dili
okay i tought you were talking about alternate reality and not about witp

No, no alternate reality here. I have my green, waste management, and reality check button turned on.

John

[mikemike]

ORIGINAL: el cid again

But XXI was not a good design - it was a technical mistake not understood as such until long after the war. It is not clear it was controllable at speed - and nobody ever dared find out. The hull shape was wrong - was substantially rationalized during the war - and the Japanese guppy's were based on "superior hydrodynamic research" - but we were so sure the Germans must be better we just sank the Japanese boats without testing. It is possible this rushed - and improvised - design was not entirely integrated in other respects.

Using the hull of the Type 18 was a compromise, but as it was already extensively tested in the model basin this cut about six months off development the time. The strength of the double-bubble pressure hull couldn't be precisely calculated at the time, so the designers worked with guesstimates. Postwar calculations with improved methods revealed that the strength of the lower pressure hull lobe had been overestimated. Several boats had reached depths of 220 m on deep-diving tests during the war. This was the designed maximum combat depth; implosion depth had been calculated as 330 m.
Much of the equipment of the type 21 had been adopted from the type 18 design, including the main reduction gear, which allowed the use of more efficient high-speed electric engines. But the type 18 had been designed by the Walther team which comprised able engineers, but nobody with submarine design experience, let alone experience in submarine operations, so many design details proved disadvantageous, like the way the propeller shafts were splayed outwards, which made the type 21s awkward to maneuver, with a resultant large turning circle. Much of the equipment was overly complicated and a departure from common German practice, which led to time-consuming teething troubles. In addition the Navy was unwilling to relinquish the idea of using the type 21 boats on surface attacks in the traditional way, although they had been provided with a superior underwater performance. The hull was shaped for surface running (which was a legacy from the type 18 design), the snorkel was an afterthought, with an awkward installation, the Navy (Dönitz) insisted on a traditional open bridge and AA armament, although Hitler himself had questioned early on the need for guns on a boat that was intended to operate mostly submerged. Of the total hydrodynamic drag of the submerged boat, 7% was due to the open bridge, 7% to the gun turrets, and a whopping 28% to the venting slits in the outer casing. The venting slits were eventually slightly reduced in area because a short diving time still was important to the navy brass. Had the type been thoroughly modified for minimized submerged resistance, submerged speed would have been about two knots higher.

The German designers knew very well that the type 21 was a hastily cobbled-up compromise; there were quite a number of less expensive designs with comparable or better performance but they never got off the drawing board. I've added as example a scan of the type 29H design (not optimum quality, unfortunately). Given enough time, the Kriegsmarine certainly would have had boats as good as or better than the Japanese Guppy types.

[el cid again]

ORIGINAL: mikemike

ORIGINAL: el cid again

My understanding is the Type XXI were indeed intended to use submerged attacks - combining sonar data and homing torpedoes - but I have the impression they hoped to use passive sonar. Active sonar is a great way to say "I am here" - and everyone for many miles is going to hear it - without even a hydrophone - you can hear it everywhere (except in the air I suppose).

I've dug out the book and reread the relevant passage. The Type 21's were to be equipped with an active/passive sonar type SU, codenamed "Nibelung". This operated at 15 kHz with a peak impulse power of 400 watts and an impulse length of 20 milisecs. Being another piece of kit that was late, only part of the subs were equipped with it. It was built into the lower forward edge of the conning tower. Maximum range against big ships was 5-10 km depending on water conditions.

Attack tactics were developed in January, 1945 in exercises near Bornholm (a Danish island in the Baltic off the Swedish coast) using four submarines against a convoy consisting of thirteen ships. The preferred tactic was as follows: search for targets with the GHG (passive sonar array, range against single ships up to 20 km,aginst convoys up to 100 km under optimum conditions).Fix target bearing with the GHG. approach the target. When close enough, steer SU in passive mode to target bearing, get a bearing fix with the SU. Then switch to active and measure target distance by single "pings". Target range, course, and approximate speed could be obtained with a minimum of three "pings". These parameters would then be used to aim the torpedoes. The majority of torpedoes used would have been FAT pattern-running torpedoes, the T5 homing torpedoes were too slow, not optimized for use against merchant ships, and probably too expensive.

The author says that an attentive ASDIC operator could have detected the SU pulses, but would have been unable to locate the source of single "pings" due to the amplitude measuring method employed.

Single pings would be fairly safe from being measured in bearing - but would say LOUDLY for all to hear "You are about to be attacked - start evasive steering at full speed" -- go to battle stations - set condition zebra - escorts attempt to localize as well.

[el cid again]

Turns out the Type 18/21 hull was not proper for controlling movement underwater - see US Submarines Since 1945 for test results.

[JWE]

ORIGINAL: treespider
But you have to remember "NEAR MISS" is simply chrome.

A HIT that inflicts a certain amount of damage will trigger a text string that reads "NEAR MISS DAMAGES..."

and a MISS may trigger a text string that reads "NEAR MISS RATTLES...."

So in the end a NEAR MISS is simply chrome because in actuality it is either a HIT or a MISS and not really a NEAR MISS.

Getting back on topic, sorry it took a while, the little green sewage treatment plant button has been working overtime.

Brother Spidey is right on the money with his comments.

You have to disassociate the “words” you read on the combat screen from the “effect” you get from the code. There is no near miss “effect”. There is only ‘damage’=0, or ‘damage’> 0 and the code looks at how much >0. If ‘damage’ is 0 you may get a text string that says ‘sub evades pattern’ or ‘near miss (ahead, astern, port, stbd) rattles sub’. This is a random selection.

If ‘damage’ >0, then how much; if minimal, then the text string call is ‘near miss (ahead, astern, port, stbd) rattles sub’, or ‘near miss damages sub’. If >minimal, other text strings come into play.

What you “see” is not necessarily what you get. The damage text calls are organized into groups of nested messages (a or b), (b or c), (c or d) with a wild card of critical damage.

The actual anti-sub algorithms have been twiddled with over the years, but the ShowMessage calls have remained the same; likely because it doesn’t make any difference.

Code is code, what you “see” is chrome.

John

[el cid again]

This seems wrong. In the sense that the game is meant to be played - we are not generating outcomes for some real application - players are supposed to be watching the messages and having fun understanding their meaning. So the mission of the program is to generate some sort of information for the players. In that sense, the messages are very important and should mean what they say. It does appear this is not always the case - but it should never be the case - and it is poor priority setting to say "it doesn't matter" - if indeed anyone ever though that. What else matters except what we tell the players in a product of this sort?

[JWE]

And along the lines of “what you see” on the combat screen is not necessarily “what you get”, there is a similar discussion on the “What’s Next” thread dealing with main vs secondary batteries.

Modders should note that “messages” are hard coded and, any tweaking of results, will still bring up the same set of “messages”. “Messages” are called in accord with a ‘window’ of hits. You can increase the probability of a hit, but if it is merely in the upper range of the text window, you will get the same “message”.

You will have to look at delta damage figures in mod tests.

Ciao. John

[akdreemer]

ORIGINAL: JWE

And along the lines of “what you see” on the combat screen is not necessarily “what you get”, there is a similar discussion on the “What’s Next” thread dealing with main vs secondary batteries.

Modders should note that “messages” are hard coded and, any tweaking of results, will still bring up the same set of “messages”. “Messages” are called in accord with a ‘window’ of hits. You can increase the probability of a hit, but if it is merely in the upper range of the text window, you will get the same “message”.

You will have to look at delta damage figures in mod tests.

Ciao. John

One of those situations where no messages would have been better, especially with FOW on.