Very interesting film - DC's v Hedgehog

Fidd · 03-01-24, 04:50 AM

Take-away points:

Reload time for the Hedgehog - 3 minutes
Claimed success rate per salvo of Hedge-hog 1 in 5. Initial success rate (non gyro-stabilised) circa 1 in 20 per salvo.
Diameter of circle of impacts - about 100'.
Claimed success rate per DC dropped (not pattern thereof) 1 in 80.
Hedgehog rounds landed ahead of the ship by circa 590' and descended at 33' per second, reaching 200' in under 9 seconds.

I think this does argue a case that our DC's are way too accurate, or way too accurate in depth, or, way too lethal? If so, this supports my contention that the ingame experience should involve much more prolonged DC attacks, largely with progressive degradation of items within the u-boat, eventually followed by an outright kill - or escape?

Hooston · 03-07-24, 10:28 AM

Need to be a bit careful with Youtube "facts" (and also subsim facts!). a couple of clips were used about eight times in that one video, and depth charges were shown when discussing hedgehog... Usually in the dark skies/seas series the script is much better than the video.

In real life the allies produced an ASDIC/hedgehog training film so incredibly boring it was used for many years by dentists during root canal treatment.

https://www.dailymotion.com/video/x7qjuo7

The problem with minimum range was more one of the fixed vertical angle at which the sound beam was projected (until late in the war). In fact the range at which contact was lost was a useful indicator of depth.
Equipment improved a lot later on but the allies never got good at establishing depth. A wide spread of depth charge settings would therefore be used. If you consider the small lethal radius of a few metres and the range of possible depths it is easy to see why the kill probability was very low, without even considering evasive manoeuvres. Conversely SH3 depth charge settings are so accurate that changing depth by 20m becomes a very reliable evasion technique.
On the other other hand game warships attack the last known position even if they have no contacts and the chances of a hit are about zero. Maybe it simulates attacking false returns from previous attacks? They give up after 20-40 minutes loss of contact instead of the late war recommended 24 hours, so stay quiet unless you are really sure they have you on ASDIC.

There's also the question of maximum settings for depth charges. I'm not very clear on this. Some sources say 300ft, increasing to 550ft very early in the war. Hard to square with the allies' operation of type VII submarine U570/HMS Graph. Other sources suggest 750ft. Sinking a deep submarine (200m/660ft or more) seemed really difficult to the end of the war and waiting for it to run out of air was often necessary.

Modders have done what they can, but the AI is hard coded in the original game.

Fidd · 03-07-24, 10:50 AM

I fully take your point about "you-tube facts", although, like you, I've found this chap to be fairly reliable where I've independent material to compare. I think we can forgive duplicated use of footage!

Regarding depths of detonations, it became a widespread practice in the RN to "soap" DC charges when the u-boat'd depth was thought to deeper than the maximum settable depth of the DC. This was simply pressing soap into the aperture through which water-pressure was measured. It rapidly dissolved in sea-water, delaying the detonation. I do not agree that it was practice to set a range of depths in each pattern, as the depth setting used was commanded by the officer in charge of the Asdic. I cannot exclude that it "never happened", but it'd be unusual I think.

I fully agree that our DC's are rather too lethal, and are woefully short in terms of for how long searches and attacks are prosecuted for. I would regard the lethal range of a DC to be 5m incidentally) For my money what needs to happen is for the de-alert to commence once the u-boat is under (say) 30m or so, and for the asdic searches and attacks to continue for at least 20 minutes, during which period, the convoy alert ceases. (to allow other u-boats to attack without being inconvenienced by that alert, unless, they in turn become detected of course!)

03-01-24, 04:50 AM	#1
Fidd XO Join Date: Apr 2005 Location: Blighty! Posts: 415 Downloads: 10 Uploads: 0	Very interesting film - DC's v Hedgehog Take-away points: Reload time for the Hedgehog - 3 minutes Claimed success rate per salvo of Hedge-hog 1 in 5. Initial success rate (non gyro-stabilised) circa 1 in 20 per salvo. Diameter of circle of impacts - about 100'. Claimed success rate per DC dropped (not pattern thereof) 1 in 80. Hedgehog rounds landed ahead of the ship by circa 590' and descended at 33' per second, reaching 200' in under 9 seconds. I think this does argue a case that our DC's are way too accurate, or way too accurate in depth, or, way too lethal? If so, this supports my contention that the ingame experience should involve much more prolonged DC attacks, largely with progressive degradation of items within the u-boat, eventually followed by an outright kill - or escape? Last edited by Fidd; 03-01-24 at 05:17 AM.

03-07-24, 10:28 AM	#2
Hooston Electrician's Mate Join Date: Jun 2020 Posts: 137 Downloads: 15 Uploads: 0	Real life is less interesting Need to be a bit careful with Youtube "facts" (and also subsim facts!). a couple of clips were used about eight times in that one video, and depth charges were shown when discussing hedgehog... Usually in the dark skies/seas series the script is much better than the video. In real life the allies produced an ASDIC/hedgehog training film so incredibly boring it was used for many years by dentists during root canal treatment. https://www.dailymotion.com/video/x7qjuo7 The problem with minimum range was more one of the fixed vertical angle at which the sound beam was projected (until late in the war). In fact the range at which contact was lost was a useful indicator of depth. Equipment improved a lot later on but the allies never got good at establishing depth. A wide spread of depth charge settings would therefore be used. If you consider the small lethal radius of a few metres and the range of possible depths it is easy to see why the kill probability was very low, without even considering evasive manoeuvres. Conversely SH3 depth charge settings are so accurate that changing depth by 20m becomes a very reliable evasion technique. On the other other hand game warships attack the last known position even if they have no contacts and the chances of a hit are about zero. Maybe it simulates attacking false returns from previous attacks? They give up after 20-40 minutes loss of contact instead of the late war recommended 24 hours, so stay quiet unless you are really sure they have you on ASDIC. There's also the question of maximum settings for depth charges. I'm not very clear on this. Some sources say 300ft, increasing to 550ft very early in the war. Hard to square with the allies' operation of type VII submarine U570/HMS Graph. Other sources suggest 750ft. Sinking a deep submarine (200m/660ft or more) seemed really difficult to the end of the war and waiting for it to run out of air was often necessary. Modders have done what they can, but the AI is hard coded in the original game.

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03-07-24, 10:50 AM	#3
Fidd XO Join Date: Apr 2005 Location: Blighty! Posts: 415 Downloads: 10 Uploads: 0	I fully take your point about "you-tube facts", although, like you, I've found this chap to be fairly reliable where I've independent material to compare. I think we can forgive duplicated use of footage! Regarding depths of detonations, it became a widespread practice in the RN to "soap" DC charges when the u-boat'd depth was thought to deeper than the maximum settable depth of the DC. This was simply pressing soap into the aperture through which water-pressure was measured. It rapidly dissolved in sea-water, delaying the detonation. I do not agree that it was practice to set a range of depths in each pattern, as the depth setting used was commanded by the officer in charge of the Asdic. I cannot exclude that it "never happened", but it'd be unusual I think. I fully agree that our DC's are rather too lethal, and are woefully short in terms of for how long searches and attacks are prosecuted for. I would regard the lethal range of a DC to be 5m incidentally) For my money what needs to happen is for the de-alert to commence once the u-boat is under (say) 30m or so, and for the asdic searches and attacks to continue for at least 20 minutes, during which period, the convoy alert ceases. (to allow other u-boats to attack without being inconvenienced by that alert, unless, they in turn become detected of course!)