Bismarck's armor against long range hits

Discussions about the history of the ship, technical details, etc.
spicmart
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Bismarck's armor against long range hits

Post by spicmart » Sun Nov 04, 2018 5:17 pm

The Bismarck design is often touted as mediocrely or badly armored against long range fire. Now I read that this has not been the case as findings of primary sources prove, that the armor scheme did take plunging shells into account. Is that really so? I think Mr. Thorsten Wahl/Thoddy and Delcyros were pioneers in that.

Maybe they (or others) can give some insight?

Bill Jurens
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Re: Bismarck's armor against long range hits

Post by Bill Jurens » Sun Nov 04, 2018 6:31 pm

It's important to realize, I think, that the extent and thickness of deck armor had to consider the threats of both incoming gunfire and aircraft bombs as well. The optimum configuration -- assuming that there was some way to determine determine exactly what that might have been ante tempus -- would be different depending upon ones assessment of the most probable -- or most dangerous threat.

There is also a tendency to assume that thicker armor is necessarily "better" than thinner armor. This is, of course, true on the face of it once impact has occurrred, but it's important to realize that increases in armor thickness do not occur in a vacuum, i.e. that in addition to their beneficial effects, increases in armor thickness can cause detrimental effects as well. Increasing deck armor thickness by 25mm on a typical battleship might cost 1500 tons or so, weight and volume which could otherwise be used to increase speed, endurance, or -- in an oft-neglected area -- crew comfort and safety. Stability issues for the moment neglected, that 1500 tons spent in increased thicknesses of splinter protection for crews in exposed positions in the superstructure instead, e.g. to mitigate the effects of strafing attacks, might result in a situation where one's ship was not even hit in the first place. Or, the weight and space might be more effectively expended in installing larger and better-equipped range-finders and plotting rooms.

In situations like this, the designer(s) must in effect try to 'guess' what tactical situation to anticipate and prepare for. No one can really see the future accurately, and so the tactical situation(s) in which their design actually participates are often quite different from the ones assessed as 'most probable' in the design office perhaps fifteen years earlier. If, in this unanticipated scenario the layout of armor etc. turns out to have been close to optimal with regard to ship survival, then the designers are celebrated as forward-looking genii. If, by coincidence, an alternate tactical situation presents itself and the designers earlier choices are seen to have been less-than-optimal, then they are often forever-after vilified by 'armchair admirals' as brainless clots.

As the old saying goes, if all you have is a hammer, then everything tends to look like a nail. In discussions like this, it's important, I think, not to over-emphasize the selection of armor distribution and characteristics, whatever they may have been, at the cost of excluding or minimizing the other equally important design characteristics that have an equal or greater effect on warship effectiveness as well.

Bill Jurens.

Thorsten Wahl
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Re: Bismarck's armor against long range hits

Post by Thorsten Wahl » Mon Nov 05, 2018 1:02 pm

aggree with @Bill Jurens

small addition
a Basic overview on the philosophy of german ballistic protection can be found in the "Unterlagen zur Bestimmung der Hauptkampfentfernung und Geschosswahl Heft a Textband"
"Recomendations for determining the main combat distance and projectile selection, textual explanations"

it also explains why the Bismarck scheme is not a "beefed up" Baden.

Full size ballistic tests and war time experience did not disclose obvious weaknesses of the german horizontal armor arrangementin the ballistic protection against artillery type projectiles available during WW2. Ballistic experiments showed a roughly similar ballistic effectiveness for the 5 cm + 8cm parts against certain type of attack as a single 15 cm plate.

One might take the
"Kriegserfahrungen mit dem Schlachtschifftyp „Bismarck/Tirpitz“, gewonnen bei Wiederherstellungsarbeiten des Schlachtschiffes „Tirpitz“ nach Angriffen mit Spezialminen und Fliegerbomben, Oberbaurat Krux"
-"War experience with the battleship type "Bismarck / Tirpitz", won in restoration work of the battleship "Tirpitz" after attacks with special mines and aerial bombs, Oberbaurat Krux"

as possible indication for a weakness in the 5 + 8 cm armor protection against AP-bomb attack as ther were several penetrations Scharnhorst and Tirpitz (but all fuzes became duds). The same bombs werent able to penetrate the 5 + 11 cm parts in any case. He concluded if one puts more emphasis on the air threat one thicker plate might be better in this case.
(the "Textband" also contains evaluations of attacks with different bomb types)
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

alecsandros
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Re: Bismarck's armor against long range hits

Post by alecsandros » Tue Nov 06, 2018 11:46 am

Thorsten Wahl wrote:
Mon Nov 05, 2018 1:02 pm
as possible indication for a weakness in the 5 + 8 cm armor protection against AP-bomb attack as ther were several penetrations Scharnhorst and Tirpitz (but all fuzes became duds).
Any thoughts on the 8 + 10cm of armor decks ?
[i.e. 8cm-thick sections of weather deck and 10cm thick sections of main armor deck]

spicmart
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Re: Bismarck's armor against long range hits

Post by spicmart » Tue Nov 06, 2018 12:00 pm

Thanks.

GiZi
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Re: Bismarck's armor against long range hits

Post by GiZi » Wed Nov 07, 2018 3:40 am

5cm + 8cm decks equalling 15cm in effective thickness?

I'm somewhat curious about this. 5cm + 8cm = 13cm, and usually the mantra about multiple plates is that they are less effective than the sum of their thickness.

Is the 15cm figure taking into account decapping, or is a different phenomenon at play?

Bill Jurens
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Re: Bismarck's armor against long range hits

Post by Bill Jurens » Wed Nov 07, 2018 4:54 am

Some tradeoffs are involved. A deck made up of a single-thickness plate, though typically somewhat more efficient ballistically, if mounted 'high' protects the interior of the ship, but negatively affects stability. A single plate thickness mounted lower, improves stability but leaves the areas above the plate more vulnerable. And, although multiple plates are typically less efficient when angles of fall are high, i.e. at obliquities close to normal, they are often somewhat more efficient and effective if the obliquity is higher, as might occur when rejecting incoming gunfire at angles of fall of (say) 15 degrees or less. (Thisis one reason why many battleships employed laminated decks in the first place.) Further, one has to (or should) try to take into account the effects of issues such as decapping, fuse action (or inaction) and the probability of encountering hull structure that is independent of the plate itself. If the angle of approach is very oblique, even a penetrating projectile is quite likely to encounter a supporting girder under the deck itself. This is also a consideration if the angle of fall is high, as might be typically encountered when dealing with a bomb. If frame spacing is a meter, and the bomb itself is (let's say) 500 mm in diameter, there is a 50% chance (roughly) that the bomb will actually strike a girder on the way through, and well over a 50% chance that it will strike close enough to a girder that the armor will be somewhat reinforced. Planning to reject both bombs and projectiles is difficult; most bombs tend to be lighter overall, of lighter physical construction, travelling slower, and approach decks more normally than projectiles do. Projectiles tend to be heavier, more robust, travelling faster, and striking much more obliquely.

There are really few simple answers to this...

Bill Jurens.

Thorsten Wahl
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Re: Bismarck's armor against long range hits

Post by Thorsten Wahl » Wed Nov 07, 2018 8:30 am

for a start
the cited Textband Unterlagen zur Bestimmung der Hauptkampfentfernung und Geschosswahl

-W Hurlich spaced Armor
http://www.dtic.mil/docs/citations/ADA954865

---------------------------------------------------------
SUPP 22-68 SPACED ARMOUR.jpg
SUPP 22-68 SPACED ARMOUR.jpg (60.93 KiB) Viewed 167 times
The problem of increased deck protection was firstly recognized by british ballistic research in
"High obliquity attack of deck Targets 12/45"
The main reason for projectile failure has been described as topple.

shortly after this report they published target properties of Tirpitz as following
vertical side armour 12 inches
deck armour 6 inches (as far as i remember correctly in SUPP 6-481) with the note that no british battleship shell available at the time was able to defeat 6 inches of horizontal protection at ranges below 30 kyard.

Unfortunately this document was not available in Kew, as it received no modern Access number such as ADM... SUPP or DEFE
compared to the following reports on high obliquity attack II and III and others.

They then systematically researched "the peculiar condition" of increased protection , wich may have some influence on projectile performance against complex (spaced)targets, as decapping, yaw(see also optimum yaw wich may increase penetration on oblique impacts), head shape of projectile, lenght of projectile, different cap types, influence of distance between the armour plates...
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

alecsandros
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Re: Bismarck's armor against long range hits

Post by alecsandros » Wed Nov 07, 2018 9:24 am

Thorsten Wahl wrote:
Wed Nov 07, 2018 8:30 am
shortly after this report they published target properties of Tirpitz as following
vertical side armour 12 inches
deck armour 6 inches (as far as i remember correctly in SUPP 6-481) with the note that no british battleship shell available at the time was able to defeat 6 inches of horizontal protection at ranges below 30 kyard.
Excuse me for insisting, but you know Tirpitz's deck armor varied in thickness - weather deck 5cm (with small areas of 8cm), and main armor deck 8cm above machinery and 10cm above magazines. Thus overall thickness was between 5+8 = 13cm to 8+10=18cm.

Did the above document work with some sort of an average of the existing armor thicknesses ?

Thorsten Wahl
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Re: Bismarck's armor against long range hits

Post by Thorsten Wahl » Wed Nov 07, 2018 2:35 pm

No detailed Information about the real thicknesses is given in the report,
Ist my conclusion as usually the "weakest point" is considered in general assumptions
------------------------------------------------------------------------------------------------------------

regarding the 8 cm wheather deck around the middle artillery
this thickness was expected to offer superior protection compared to cruisers, they had to deal with primarily.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

alecsandros
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Re: Bismarck's armor against long range hits

Post by alecsandros » Wed Nov 07, 2018 7:59 pm

I don't understand the cruiser part.....
Was the 8cm portion thicker to protect against 8" gunfire ?

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