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Catfish · 01-10-11, 02:32 PM

Hello,
thanks for answering to my rant ahem - sorry

1st the developers can certainly not be made responsible what a later mod does lol, and yes, IRAI is hard (a word that is a plain understatement in the australian sense of expressing an extreme) lol

2nd i should have started with the vanilla game just to try it out, but when i read about those mods ...

Ok, it may have been me who already brought up the question about accuracy and sensitivity of allied sensors already in SH4 (U-Boat missions, OMEGU etc.). I cannot remember who posted this picture/diagram of a destroyer and which active sonar was able to scan which angle before and under the bow.
Things went downhill fast after 1943 for the U-boats i know, and certainly more than two destroyers using Walker's method usually killed a boat, if not so early before the US coast, or in the open atlantic.

Let's say i have to accept if someone tells me what the capability of ASDIC was back then but i doubt the destroyers and DEs had all those new systems immediately built-in, and it certainly needed a seasoned crew to really use it to full advantage - but in 1942 ?

ASDIC did not help England at first, because the boats were attacking surfaced, at night. The flower class corvettes had a top speed of 15 knots and the U-boats with its 18 knots just ran away, their silhouette making them almost invisible against gunfire.

There are a lot of acounts where destroyers, sloops or corvettes passed boats by less than 50 meters without seeing them, let alone firing at them in rough wheather even if they happened to see it. Some commanders swung their boat around and hid away in their own Diesel exhaust fumes. From an elevation like a destroyer deck it is unbelievably hard to see a near low dark silhouette at night or rough weather.

Even with radar a destroyer could not "see" a boat under 1000 meters, so if the boat made a sudden turn in rain, fog, storm, night etc. its enemy would just run past it.
And not all destroyers had radar early in the war, not all had experienced crews and they were so few that they had to stay with the convoy after a short search. Let alone few were real destroyers, but all kinds of boats pressed into convoy service.

The problem was that once the allies were aware of the 200+ meters diving depth and having cross bearings, going deep did not help the U-boats anymore, if there was no temperature/density layer.

The thing with submerged boats at PD not being detected:
It is possible to detect subs at PD, but you need some real good sea conditions. But from all i read it is almost impossible at some 12-14 meters of depth in anything but calm seas, there is too much surface noise for hydrophones, and the ASDIC of the time was not doing so well even in 1945 - you cannot compare this with modern systems or even with systems that only were available in 1945. It is theoretically easier in shallow waters, but there are other effects that spoil the target solution. Hardegen makes that quite clear when hiding in very shallow waters, at 20 meters on the ground, and some escorts buzzing across his fore deck but throwing their charges some 100 meters off.

There is a minutely detailed report of how a VIIc boat attackss a convoy in the eastern channel waters at pd in late 1944, and how he managed to sink one steamer, and still evade the destroyers - all at periscope depth.

There are other reports from the later small XXIII "coastal" boats who did just that. The hydrophone and the situation awareness by being able to observe the escorts, along with their small hull made them perfect for such kind of warfare.
As well there are other reports of tests done right after the war with ordinary (if late-built) VIIc boats, which could not be detected at pd with the most recent sensor arrays.

In the book on U-2540 (the boat now being in Bremerhaven as a museum ship being thoroughly tested after the war in the NATO) there is an article of how to evade at periscope depth as well. This was however not always a good idea since planes could sometines spot the boat from above.

When they tried to measure the speed of the V80 Walther boat they were not able to hear it in the hydrophones despite the boat making 20 knots, at 20 meters depth, and ASDIC did not work as well (this in a british report about testing a real Walther boat (with the Junkers steering colums running on Perhydrol fuel)).

I base my views on the following books, and some more:
- "U-Boot und U-Boot-Jagd" (GDR 1969) mostly dealing with Diesel boats and how to detect them
"Die Woelfe und der Admiral", Frank 1953
- "So war der U-Bootkrieg", Busch 1957
- "U 333", Ali Cremer 1982
- "Geschichte des U-Bootkriegs", Peillard
- "Heimfahrt der U 720", Lehnhoff
and 5 or so others i can list later if you want.

IRAI makes it look as if the destroyers and crews of 1945 had teleported back to 1942, leaving no chance for a boat to attack surfaced or submerged at all; but i realized it can be toned down, so i will test it a bit. I am just about to install the new big Opus Magnum mod -

And i want to express my thanks and admiration for the people who make those mods possible !

Thanks and greetings,
Catfish

P.S.
i just thought about how this "detecting" is done in SH V, or with TDW's IRAI ? Is it done with some percent of randomness, e.g. the destroyer listens or uses active sonar, and detects you at (for the sim) favourable conditions with a probabability of say 10 percent ? SO he will detect you statistically in one of ten sweeps, ok. BUT: If this sweep has a time of say 1 minute until the next, it is likely that he will surely detect you within 10 minutes - how is it done ?

P.P.S.
Just finished the Gibraltar mission, but man was that hard !
I followed the advice and initially ran surfaced at top speed to make it in those eight hours. In the beginning it is dark, but the night vanishes at around 0.30 pm.
So i ran along the northern coast and only slowed down when a destroyer came REALLY near. Unfortunately there must be 6-7 hunter groups with some 3 ships each, but they (thank god) run towards the center of the strait away from the coast, and they never saw me. When i was close to Gibraltar there was a destroyer anchored near the coast. Getting cocky I dived, crept past him, and sunk him with a rear torpedo. Then i immediatly surfaced and ran at 7 knots for 3 minutes until i saw some escorts heading for the explosion point. I shortly dived until they were past me, then surfaced and, reaching the entrance of Gib's port, i turned the boat right to 150 degrees and ran to the middle of the strait with 6 knots, straight towards another destroyer passing the strait from west to east. It was already getting brighter, and when i was close i dived to pd and ran on silent, again turning to 110 degrees. The destroyer, being faster than me ran on past me and vanished. Now all around my periscope was clear, but i could not surface -too bright sky now and i even saw a plane !
I had 4 hours left and decide to stay at pd until i realized visibility was suddenly down to some 50 meters - rain and fog !
I immediately surfaced, went to full speed without charging batteries at 17 knots and did so for 10 minutes until half the entrance of the Gib port entrance, until i received the message "radar detected". I ran on for a minute, turned south to 150 degrees to divert them, and made a crash dive at full speed. At 50 meters i switched to silent running and changed my course east to 080. As i could see with the periscope lots of light beams above and all hell broke lose. I did not dare to get deeper than 150 meters since my boat does not seem to like that, but indeed managed to go straight on until they gave up - they were searching in the wrong direction, and i was lucky.
I swear i was sweating at times ..

01-10-11, 02:32 PM	#10
Catfish Dipped Squirrel Operative Join Date: Sep 2001 Location: ..where the ocean meets the sky Posts: 17,767 Downloads: 38 Uploads: 0	Hello, thanks for answering to my rant ahem - sorry 1st the developers can certainly not be made responsible what a later mod does lol, and yes, IRAI is *hard* (a word that is a plain understatement in the australian sense of expressing an extreme) lol 2nd i should have started with the vanilla game just to try it out, but when i read about those mods ... Ok, it may have been me who already brought up the question about accuracy and sensitivity of allied sensors already in SH4 (U-Boat missions, OMEGU etc.). I cannot remember who posted this picture/diagram of a destroyer and which active sonar was able to scan which angle before and under the bow. Things went downhill fast after 1943 for the U-boats i know, and certainly more than two destroyers using Walker's method usually killed a boat, if not so early before the US coast, or in the open atlantic. Let's say i have to accept if someone tells me what the capability of ASDIC was back then but i doubt the destroyers and DEs had all those new systems immediately built-in, and it certainly needed a seasoned crew to really use it to full advantage - but in 1942 ? ASDIC did not help England at first, because the boats were attacking surfaced, at night. The flower class corvettes had a top speed of 15 knots and the U-boats with its 18 knots just ran away, their silhouette making them almost invisible against gunfire. There are a lot of acounts where destroyers, sloops or corvettes passed boats by less than 50 meters without seeing them, let alone firing at them in rough wheather even if they happened to see it. Some commanders swung their boat around and hid away in their own Diesel exhaust fumes. From an elevation like a destroyer deck it is unbelievably hard to see a near low dark silhouette at night or rough weather. Even with radar a destroyer could not "see" a boat under 1000 meters, so if the boat made a sudden turn in rain, fog, storm, night etc. its enemy would just run past it. And not all destroyers had radar early in the war, not all had experienced crews and they were so few that they had to stay with the convoy after a short search. Let alone few were real destroyers, but all kinds of boats pressed into convoy service. The problem was that once the allies were aware of the 200+ meters diving depth and having cross bearings, going deep did not help the U-boats anymore, if there was no temperature/density layer. The thing with submerged boats at PD not being detected: It is possible to detect subs at PD, but you need some real good sea conditions. But from all i read it is almost impossible at some 12-14 meters of depth in anything but calm seas, there is too much surface noise for hydrophones, and the ASDIC of the time was not doing so well even in 1945 - you cannot compare this with modern systems or even with systems that only were available in 1945. It is theoretically easier in shallow waters, but there are other effects that spoil the target solution. Hardegen makes that quite clear when hiding in very shallow waters, at 20 meters on the ground, and some escorts buzzing across his fore deck but throwing their charges some 100 meters off. There is a minutely detailed report of how a VIIc boat attackss a convoy in the eastern channel waters at pd in late 1944, and how he managed to sink one steamer, and still evade the destroyers - all at periscope depth. There are other reports from the later small XXIII "coastal" boats who did just that. The hydrophone and the situation awareness by being able to observe the escorts, along with their small hull made them perfect for such kind of warfare. As well there are other reports of tests done right after the war with ordinary (if late-built) VIIc boats, which could not be detected at pd with the most recent sensor arrays. In the book on U-2540 (the boat now being in Bremerhaven as a museum ship being thoroughly tested after the war in the NATO) there is an article of how to evade at periscope depth as well. This was however not always a good idea since planes could sometines spot the boat from above. When they tried to measure the speed of the V80 Walther boat they were not able to hear it in the hydrophones despite the boat making 20 knots, at 20 meters depth, and ASDIC did not work as well (this in a british report about testing a real Walther boat (with the Junkers steering colums running on Perhydrol fuel)). I base my views on the following books, and some more: - "U-Boot und U-Boot-Jagd" (GDR 1969) mostly dealing with Diesel boats and how to detect them "Die Woelfe und der Admiral", Frank 1953 - "So war der U-Bootkrieg", Busch 1957 - "U 333", Ali Cremer 1982 - "Geschichte des U-Bootkriegs", Peillard - "Heimfahrt der U 720", Lehnhoff and 5 or so others i can list later if you want. IRAI makes it look as if the destroyers and crews of 1945 had teleported back to 1942, leaving no chance for a boat to attack surfaced or submerged at all; but i realized it can be toned down, so i will test it a bit. I am just about to install the new big Opus Magnum mod - And i want to express my thanks and admiration for the people who make those mods possible ! Thanks and greetings, Catfish P.S. i just thought about how this "detecting" is done in SH V, or with TDW's IRAI ? Is it done with some percent of randomness, e.g. the destroyer listens or uses active sonar, and detects you at (for the sim) favourable conditions with a probabability of say 10 percent ? SO he will detect you statistically in one of ten sweeps, ok. BUT: If this sweep has a time of say 1 minute until the next, it is likely that he will surely detect you within 10 minutes - how is it done ? P.P.S. Just finished the Gibraltar mission, but man was that hard ! I followed the advice and initially ran surfaced at top speed to make it in those eight hours. In the beginning it is dark, but the night vanishes at around 0.30 pm. So i ran along the northern coast and only slowed down when a destroyer came REALLY near. Unfortunately there must be 6-7 hunter groups with some 3 ships each, but they (thank god) run towards the center of the strait away from the coast, and they never saw me. When i was close to Gibraltar there was a destroyer anchored near the coast. Getting cocky I dived, crept past him, and sunk him with a rear torpedo. Then i immediatly surfaced and ran at 7 knots for 3 minutes until i saw some escorts heading for the explosion point. I shortly dived until they were past me, then surfaced and, reaching the entrance of Gib's port, i turned the boat right to 150 degrees and ran to the middle of the strait with 6 knots, straight towards another destroyer passing the strait from west to east. It was already getting brighter, and when i was close i dived to pd and ran on silent, again turning to 110 degrees. The destroyer, being faster than me ran on past me and vanished. Now all around my periscope was clear, but i could not surface -too bright sky now and i even saw a plane ! I had 4 hours left and decide to stay at pd until i realized visibility was suddenly down to some 50 meters - rain and fog ! I immediately surfaced, went to full speed without charging batteries at 17 knots and did so for 10 minutes until half the entrance of the Gib port entrance, until i received the message "radar detected". I ran on for a minute, turned south to 150 degrees to divert them, and made a crash dive at full speed. At 50 meters i switched to silent running and changed my course east to 080. As i could see with the periscope lots of light beams above and all hell broke lose. I did not dare to get deeper than 150 meters since my boat does not seem to like that, but indeed managed to go straight on until they gave up - they were searching in the wrong direction, and i was lucky. I swear i was sweating at times .. Last edited by Catfish; 01-13-11 at 02:42 AM.