Bismarck class turret protection

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alecsandros
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Re: Bismarck class turret protection

Postby alecsandros » Fri Apr 19, 2013 10:05 am

delcyros wrote:if we assume a 10% quality advantage for british CA against KC/n.A

Why this assumption ?

but DUNKERQUE´s case is unique as they employed face hardened armour on the flat turret roofs

Yes, but Dunkerque had 15cm thick roofs for the main turrets, and Hood was firing from 15-16km distance.
Expected angle of fall of British 15"/L42 at 16km is about 17*.

The problem was that Dunkerque's turret top had an angled surface, at about 9* from the horizontal.
Thus theoretical impact obliquity may have been ~ 26* at best [17* angle of fall + 9* plate inclination]. However, real life obliquity would have been worse, as the turret would not have been oriented exactly towards Hood [thus adding a lateral obliquity].

Expected penetration of 15"/L42 at 26* would be ~ 100mm homogenous.

French cemented armor was based on Krupp WW1 cemented armor, which featured about 30-35% cimentite at the front, gradualy falling back in hardness and brittleness towards the back of the plate.

Another big question remains about the quality of French cemented armor, but lacking definitive documents, I don't know what to say.

Anyway, 15cm of armor (even cemented) broken up at 16km distance is quite an accomplishment

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Re: Bismarck class turret protection

Postby delcyros » Fri Apr 19, 2013 11:54 am

Why this assumption ?


Out of convenience. Data are in part contradictive but it´s likely that KC/n.A. was right between brit. CA and US class A in stopping quality according to post war trials -at least as far as thick plates engaged by major calibre APC is concerned.


Sure it was 15cm?
I know that STRASSBOURG´s perhaps were but DUNKERQUE´s? I ask specifically, because the post damage examination of DUNKERQUE says explicitely that the turret roof was just 80mm, which makes a lot of sense given the fact that the DUNKERQUE´s were primarely a response to the 11"/52 armed Panzerschiffe.

The relevant document is labelled "Bericht über den Besuch des Schlachtschiffes "DUNKERQUE" in Oran, 24. Sept. 1940", dated to 2nd of oct. 1940 and provided by the italian cease fire commission, department of the navy. p.9 I quote

"Die Turmdecke hat nur 8 cm Dicke. Daraus erklärt sich das Herausstanzen bei einem Auftreffwinkel von nur 13 Grad."
(emphasized in original)

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Re: Bismarck class turret protection

Postby alecsandros » Fri Apr 19, 2013 12:53 pm

delcyros wrote:
Why this assumption ?


Out of convenience. Data are in part contradictive but it´s likely that KC/n.A. was right between brit. CA and US class A in stopping quality according to post war trials -at least as far as thick plates engaged by major calibre APC is concerned.

I'm sure you've seen the US data trials performed on already damaged KC nA plates,
and also the BRitish data trials performed repeatedly on Tirptiz 12.6" plates ?

Most recent analysis I've seen indicate KC nA to be very similar to British post-1930 CA in terms of stopping power of WW2-era APC shells, with variations of +/- 2-3% in impact velocity required for complete penetrations.
Note that +/-2-3% variation can easily come from slight variations in individual plate quality, and / or individual APC shell (and gun) quality...

Sure it was 15cm?

Good question,

Dumas and G&D mention 150mm thick turret roofs for Dunkerque...and 16cm for Strasbourg.

The document you mentioned may be altered or incomplete... [on Dunkerque, 2 of the secondary quad turrets had 8cm thick roofs]

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Re: Bismarck class turret protection

Postby Thorsten Wahl » Sat Apr 20, 2013 7:13 pm

Turret protection Dunkerque
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Dunkerque turret.png
Dunkerque turret.png (4.78 KiB) Viewed 2465 times
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Re: Bismarck class turret protection

Postby paul.mercer » Sun Apr 21, 2013 8:00 pm

Gentlemen,
If one can imagine one's head in a bucket when someome hits it with a hammer - would not the concussion of a ton or more of shell hitting a turret have the same effect on those inside?

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Re: Bismarck class turret protection

Postby tommy303 » Mon Apr 22, 2013 3:05 am

Indeed, and one might have to contend with high velocity spalls broken off the back of the plate even if the shell failed to penetrate.

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Re: Bismarck class turret protection

Postby Dave Saxton » Mon Apr 22, 2013 4:35 am

If one applies the striking velocity and angle of fall for the Hood's 15" to the Gkdos curves for the heavier 15" vs face hardened plate; it shows that the Hood's 15" should have penetrated in broken condition Dunkerque's roof plate. Had it been homogenous armour of the quality of Wh then the proper curve show no chance of penetration.
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Re: Bismarck class turret protection

Postby Thorsten Wahl » Mon Apr 22, 2013 2:25 pm

Follow the Links
is this the damage to the turret
but subtitle says its Strasbourg

http://www.maritimequest.com/warship_di ... sbourg.jpg
http://www.maritimequest.com/warship_di ... sbourg.jpg

looks like a combined failure of plate cracking and failure of holding structure
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Re: Bismarck class turret protection

Postby delcyros » Mon Apr 22, 2013 6:14 pm

Isn´t that STRASSBOURG, the picture taken at Toulon somewhere 1944/5?

Dumas and G&D mention 150mm thick turret roofs for Dunkerque...and 16cm for Strasbourg.

The document you mentioned may be altered or incomplete... [on Dunkerque, 2 of the secondary quad turrets had 8cm thick roofs]


It´s possible that the authors of the document are in error but it appears improbable that the document was altered or is incomplete (as far as this question is concerned).
Following the angle of holes in the side shell from penetrating main belt hits 2&3, it was established that the angle of fall was just 13 degrees for the 15 in APC. Thus, the impact angle was 13 deg + slope (measured from the horizontal), not 13 deg in total. This is clearly an error from the authors but I have problems thinking that navy attachee´s, visiting the damage and state of repairs would have difficulties to differentiate between 8cm and 15cm thick plates on the turret roof. We can exclude that the secondary turrets are mentioned (they weren´t even hit), and the aspect is discussed under the aspect main turrets, thus explicitely mentioning 33cm main gun turrets.
What I can think of, right now is:
Either, they were told deliberately a wrong plate thickness by the french and were unable to examine the damage in the turretroof physically, or
the plate was indeed 8cm, at least on the precise locality where hit

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Re: Bismarck class turret protection

Postby alecsandros » Tue Apr 23, 2013 6:26 am

delcyros wrote:
Either, they were told deliberately a wrong plate thickness by the french and were unable to examine the damage in the turretroof physically, or
the plate was indeed 8cm, at least on the precise locality where hit


... both can be plausible explanations.

My impression is that having only 8cm of armor on the top of the turrets would have constituted a big flaw for Dunkerque's armor scheme, especialy as the roofs were built to resist AP bombs, thus requiring a considerable amount of armor.

The coincidence of having 8cm of armor on the secondary quads, the same thickness as the one mentioned in the document, seems quite interesting to me.
Naturaly, the secondaries weren't hit, but in the game of dis-information, the best method is many times to intoxicate the enemy with plausible errors...

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Re: Bismarck class turret protection

Postby paul.mercer » Tue Apr 23, 2013 8:27 pm

tommy303 wrote:Indeed, and one might have to contend with high velocity spalls broken off the back of the plate even if the shell failed to penetrate.

Thanks Tommy,
Presumably the shock of the impact plus the exploding shell causes the spalls to fly around killing or wounding the turret crew, if this is the case then surely a shell does not have to penetrate to put the turret out of action, I believe that a shell hit on a tank has the same effect.
One thing that still puzzles me, some of the posts suggest that the German 15" shell was more effective that the British 16", I would have thought that a hit from either would be pretty nasty, with the 16" having the edge due to its greater weight. Whoever is right, it cannot be denied that Rodney's 16" had a devastating effect on Bismarck.

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Re: Bismarck class turret protection

Postby alecsandros » Wed Apr 24, 2013 5:21 am

paul.mercer wrote:
tommy303 wrote:Indeed, and one might have to contend with high velocity spalls broken off the back of the plate even if the shell failed to penetrate.

Thanks Tommy,
Presumably the shock of the impact plus the exploding shell causes the spalls to fly around killing or wounding the turret crew, if this is the case then surely a shell does not have to penetrate to put the turret out of action, I believe that a shell hit on a tank has the same effect.


... Perhaps, but sometimes there wasn't any spalling caused.
Take Jean Bart for instance. Her 15" turret was hit directly by a 1227kg AP shell, which failed to penetrate. I have not seen any record concerning turret crew casualties, and without the second 16" hit, that hit the barbette and jammed the turret's rotation, the 15" guns would probably have continued to fire...

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Re: Bismarck class turret protection

Postby Ersatz Yorck » Thu Apr 25, 2013 2:25 pm

There were numerous non-penetrating turret hits at Jutland that put the turret out of action in various ways for a shorter or longer time. Conversely, there were quite severe penetrating hits to turrets that only put the turret out of action for a short time, or only knocked out one of the two guns. So basically, with a turret hit, anything can happen.

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Re: Bismarck class turret protection

Postby Ersatz Yorck » Thu Apr 25, 2013 2:58 pm

On reflection, this discussion is a bit like sex. There is alot of focus on penetration, but in fact there are a lot of other interesting things that can happen :-)

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Re: Bismarck class turret protection

Postby tommy303 » Thu Apr 25, 2013 7:07 pm

Perhaps, but sometimes there wasn't any spalling caused


True. Much depends on shell velocity and striking angle relative to the plate, shell size, plate thickness, and the metalurgical characteristics of the plate itself.

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