Bismarck/Tirpitz = most powerfull European battleships

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JtD
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by JtD »

I'd say the 130mm turret tops would be a match for the 50+100 found over Tirpitz magazines, not for the 50+80 of the machinery. And, interestingly, with C1h = 660, C2=720 and C = 660 this is exactly what you'd get from Gerzke.

Weren't the British using short fused shells that would fuse on the upper deck and detonate before having the chance to penetrate the main deck anyway?

I have read that the British did do long range tests in between the wars achieving penetrations of 6" and more, which is one of the main reasons they started upgrading the horizontal armour like mad. Hood was supposed to an additional 6" main deck armour based on these test results.

APP# 30 - is there more to that designation so that I could track it down?
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Thorsten Wahl »

First of all

the Krupp formula is a tool for calculation of a penetration, it is not physical exact, but it is able to present the expected result of a certain pentration witout beeing to complicated
with sufficient accuracy especially for german projectiles, It was not expected to explain all possible effects on the penetration of armor plate.

The whole formula was calibrated on real shell design (called optimal design) against a special material to match real penetration data.
an adoption was nearly similar shell design should achieve nearly similar penetration results,
as some of the german shell designs were very similar in their relative performance there is partially only a small difference in the C value

The formula also includes projectile weight and diameter. At the end the only unknown variable was C wich was taken as relative performance compared to the "optimal design"
Higher C result in a higher naval ballistic limit of the armor shell combination
better armor increases the C and better shell decreases C
so it was relatively easy to predict performance of foreign shells whitout knowing all paramters of the design

If you have real penetration results you can derive the value of C for this armor shell combination
its somewhere described in the document.

Similar for the coefficient B wich was a angle correction factor

The formula has its limitation especially when
-shell design and/or armor material properties strongly differs from the calibrating material/shell combination.
-very thick/thin plates
-high obliques 80+°
-no penetration occurs because of ricochet or non nose first impacts
-or somthing else irregular

Dave made a mistake when he uses C only as material coefficient and then deriving a overall performance of a two plate system. Im sorry but i didnt see this before. :oops:


Using a single plate should have the following advantages
in general a single plate of x should be able to absorb roughly 35 % more enrgy as 2 plates of x/2 thickness.
deflection towards plate normal additional reduces the efficiency of plate 2

but on a spaced array all or some of the following effects can occur
ignition of the charge before it reaches the second plate
when thickness of plate 1 was sufficent to cause decapping so the shell loses some weight and also
the head shape changes and the overall performance should diminish.
Especially high oblique performance should lowered drastically, as the cap helps in "biting" into the plate surface.
or the second plate is a fh-plate
Possible some breakage and or deforming of the projectile (could also affects fuze)
Additional some kind of yaw could be introduced, this means direction of flight differ significantly from orientation of the shell, here the remaining distance between the plates was of essential importance. (too low distance could improve penetration abilities of the shell, so this could be an contraproductive feature)

The sum of these effects can considerably exceed the loss of performance by dividing the plate. According to my citing somewhere obove in the thread the net effect can be expected up to 130%-150% of single plate performance.

If this works for the horizontal protection like it worked for the vertical protection, it was a clever way to save weigth.

At last I have to say there were strong hints, that it could be, but the last evidence is missing. The x APP could bring some enlightenment.
I have looked for this document at the national archives London, but the informations I have were not sufficient to bring this document up.
Nothing particularly new that I can see.
thats correct,. This knowledge is something around 70 years old. And it seems to me that a lot of people dont takes note of it, as it is no part of a serious discussion, or its just ignored.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by JtD »

Saves 30-50% if the first plate breaks up the projectile.

So when does that happen? Certainly doesn't when a 400mm shell hits a 50mm plate at 30°. Or a bomb get dropped.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Bgile »

Dave Saxton wrote:Note that the Bismarck's turrets tops were 130mm single plate Wh to attain an IZ requirement to 30,000 meters vs 15" shell fire. It would be highly unlikely that they would design and accept a deck protection system, which did not provide a min deck protection at least matching this specification.
Why? The Iowa class turret tops were 7.25" thick. That was quite a bit thicker than the US deck protection, wasn't it? Turret penetration implies possible magazine explosion, where deck protection over machinery spaces often doesn't, unless of course there is no splinter armor between magazine and engineering space.

Also, why couldn't yaw act to increase armor penetration? Suppose the shell was yawed toward a more beneficial angle of impact instead of the assumed detrimental effect? Okun figured the shell would be deflected downward when passing through the upper deck of Bismarck. couldn't yaw have a favorable effect as well?

Can you tell me again why the navies other than Germany adopted a more or less "AON" system when the Germans didn't? I was under the impression that the reason AON was adopted was that tests revealed it performed better than multi plate systems. I think we might have lost sight of this with all the info on why the German system supposedly worked better. Why would pre war tests give differing results to post war tests? Also, if the USN developed the new 16" shell to defeat AON, wouldn't it concern them that not all navies used AON and specifically Germany didn't? This shell is quite different from the British 16" shell used in their post war tests. I believe you have indicated you thinbk the British shell was better at deck protection than the US shell (it's shorter), but I'm not convinced. That would indicate the older US shell was as well, and therefore there would be no reason to switch. The USN went to a lot of trouble and expense to change to the new shell, and your implication is it was worse than the old one. This defies logic. It had to be significantly better to go to that much trouble to change to it.

Sorry if I'm rehashing here, but I've gotten confused with all the turns of the various threads.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Lutscha »

Thanks for the summary, Thorsten.

So what we have is, that if the projectile breaks up, the spaced array can be 30-50% more effective, which is not going to happen with the 50mm Oberdeck. If the projectile gets decapped (which it does) and yawed correctly, spaced arrays can be 10-20% more effective than a single plate. If it's yawed in a detrimental way the Oberdeck would decrease overall protection and the 80-100mm Panzerdeck would/could be better without the Oberdeck, correct?

So BS deck armour equates to 50 + 80-95mm +10-20% or 50 +80-95mm -X%, right?

What results do we have for British projectiles against the BS or TP like arrangements? I have only seen the one, were the plates were much thicker. Then of course the American shells were different, did they do some comparable tests?
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

JtD wrote:I'd say the 130mm turret tops would be a match for the 50+100 found over Tirpitz magazines, not for the 50+80 of the machinery. And, interestingly, with C1h = 660, C2=720 and C = 660 this is exactly what you'd get from Gerzke.

Weren't the British using short fused shells that would fuse on the upper deck and detonate before having the chance to penetrate the main deck anyway?

I have read that the British did do long range tests in between the wars achieving penetrations of 6" and more, which is one of the main reasons they started upgrading the horizontal armour like mad. Hood was supposed to an additional 6" main deck armour based on these test results.

APP# 30 - is there more to that designation so that I could track it down?

Note that 80mm+50mm=130 mm, and I seriously doubt that is coincidental. It's enterily plausible that because of de-capping and other factors touched upon that they knew that c1h/c could be raised to the point that VII>=VI, and they could attain at least 1:1 effective thickness.

APP Special #30 is the only name of the Document I know. It may be included in the ADM281 collection? The observation that 6" deck penetration at less than 30km battle range was not obtained was attributed to the 1.4 caliber radius of the head of the AP shell. The problems of relatively poor penetration performance at oblique striking angles caused by the head shape was noted in 1943 testing as well. As result of the post war testing they reccomened that future British AP projectile design adopt a 1.0 caliber radius head. German and American shells already featured blunter head shapes than this. The significant advantage of a blunt head shape during deck penetration is essentially nullified by yaw. This gives a spaced array a significant advantage relative to a single plate system against oblique attack by blunt head penetrators.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

Bgile wrote: ..Also, why couldn't yaw act to increase armor penetration? Suppose the shell was yawed toward a more beneficial angle of impact instead of the assumed detrimental effect? Okun figured the shell would be deflected downward when passing through the upper deck of Bismarck. couldn't yaw have a favorable effect as well?.....
Any and all yaw is determinatal to penetration. It never works in favor of penetration. If the yaw is slightly nose up by the time it reaches the main armour the necessary velocity can be as much as 30% greater than it would have been had it struck optimally nose on. It can still require more than 10% more V striking yawed nosed down. This goes some distance in making up for any potential losses of enegery consumption by using two plates instead of one.

Yaw is not trajectory change, nor does it alter the striking angle. Mr Okun incorrectly used the term yaw when describing trajectory change as a result of penetrating a plate. Usually the trajectory will change slightly toward the normal, but not always. If the shell had some nose up in flight yaw before striking the first plate the trajectory change would actually be away from normal according to US National Laboratory testing. Now we know the reason why the battery deck was 6mm and not 20mm, considering it was at point 1/2 the distance of the interspace and would be struck with approx. 1/2 the eventual precession having occured.

The amount of any trajectory change toward the normal is insignificant in the case of the Bismarck system. Wh at 80kg/mm2 will cause a ~4* trajectory change if the plate thickness is 50% the diameter of the shell. The value of trajectory change caused by a 50mm Wh upper plate when dealing with battleship caliber projectiles is a nonfactor. Furthermore, the upper armoured deck and the panzer deck are not exactly parallel in the case of the Bismarck class.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

JtD wrote:Saves 30-50% if the first plate breaks up the projectile.

So when does that happen? Certainly doesn't when a 400mm shell hits a 50mm plate at 30°. Or a bomb get dropped.
Thorsten wrote:
but on a spaced array all or some of the following effects can occur
ignition of the charge before it reaches the second plate
when thickness of plate 1 was sufficent to cause decapping so the shell loses some weight and also
the head shape changes and the overall performance should diminish.
Especially high oblique performance should lowered drastically, as the cap helps in "biting" into the plate surface.
or the second plate is a fh-plate
Possible some breakage and or deforming of the projectile (could also affects fuze)
He did not say that the viability of a spaced array was dependent upon the first plate breaking up, as in shattering the shell. Obviously the shell will only be slightly damaged to some extent, but it will certainly be de-capped by the 50mm upper deck at the typical striking angles of deck hits. This significantly reduces the prenetrability of the shell if the main armour has a tensile strength greater than 80kg/mm2, but perhaps more importantly the removal of the shells cap sets up the shell so that it is highly likely to be broken or rendered inert upon further impact with the main armour-moreso the longer per caliber the shell.

He did write:
The sum of these effects can considerably exceed the loss of performance by dividing the plate. According to my citing somewhere obove in the thread the net effect can be expected up to 130%-150% of single plate performance.
This is well put, and basically says what I have been trying to convey, only much more concise.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Lutscha »

The document cited by Thorsten says that the increase in protection is about 30-50% when the shell breaks up and 10-20 % if it is decapped and/or yawed. This document also says that yaw can improve penetration but maybe they are referring to the shell being deflected to the normal.

download/file.php?id=289

But Thorsten should be able to tell us what he meant... ;)
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Bgile »

At least part of the theory behind two plates being better than one is the decapping and resulting loss of shell mass on the first deck. Didn't the people who considered one deck better than two know this? They must have, so why would they think two plates were worse than one? Why would AON even be considered?

Why design an entirely new shell requiring heavier and more expensive loading equipment and which your older 16" gunned ships couldn't use, just so your ships could be less effective at their intended use? A shell which was worse than the existing 16" shell. There is something wrong here.

Of course, there is also the implicit idea that when a heavy shell passes through the upper deck (or upper side armor) it will just vaporize and not do any significant damage to the ship. The AON ships do protect a larger internal volume from battleship caliber shells. The German system provides more protected volume from cruiser fire.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

Actually the American system is a two plate system. Really a three plate system taking into consideration the laminate.

The Littorio system is also spaced array.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Bgile »

Dave Saxton wrote:Actually the American system is a two plate system. Really a three plate system taking into consideration the laminate.

The Littorio system is also spaced array.
Yes, I understand ... actually three plates on the Iowas because there is a spall catching deck below the MAD.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

I'm ignoring the spall catching deck as it won't do anything but maybe...well catch spalls... assuming there are any from a homogenous armour deck above. The MAD on USN BBs consists of two plates. In North Carolinas case it was 36mm +88mm-100mm, for example. The British discovered that two plates in direct contact with each other actually perfomed well less than if the two plates were spaced. The equation Vnot= (square root) (V1^2 +v2^2) would likely refect the effective MAD. This may be why British publications and documents will oft times ignore the backing plate of laminates when listing plate thickness.

A USN document refers to the upper 38mm deck on new battleships as a yaw deck, and it means that spaced array principles were in play here as designed, and were essential to the proper function of the overall system.

I'm contually struck by the how much alike German and USN designs are alike in many ways.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

Lutscha wrote:The document cited by Thorsten says that the increase in protection is about 30-50% when the shell breaks up and 10-20 % if it is decapped and/or yawed. This document also says that yaw can improve penetration but maybe they are referring to the shell being deflected to the normal.

download/file.php?id=289

But Thorsten should be able to tell us what he meant... ;)

The document linked to is pretty self evident. The context of which the term yaw is spoken of in that particular sentence is trajectory change rather than nutation and precession behavour. It also implies that with decapping and yaw; effective thickness from 110-120% the sum thickness are possible.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by phil gollin »

Dave Saxton wrote:
......... but it will certainly be de-capped by the 50mm upper deck at the typical striking angles of deck hits. ........


No. Whilst the cap fixing to the body of the shell may be broken (not a definate but a function of statistics again) the cap may continue to act together with the main body of the shell as a full AP projectile.

Two further notes.

There are numerous WW2 and post-WW2 British trials on the actions of two plates (combined and separtaed) and also yaw tests. Whilst the main one is being quoted here there are others trials which actually gave contrary indications.

The real people who should be looking at this problem are NOT WW2 naval historians, nor mid-50s to mid-90s tank experts (where an awful lot of work on yaw took place) but the 90's onwards hydrodynamicists who work on the present armour penetration computer problems.

.
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