Bismarck/Tirpitz = most powerfull European battleships

[Dave Saxton]

For the entertainment and education of all I will qoute some important parts of what was written concerning two plates and naval two plate systems of specific design:

"Since VII > VI it indicates that an arrangement of two plates requires a greater striking velocity for penetration than a single plate equal in thickness to the sum of the thickness of the two plates if:..."

The formula that the product must be greater than 1 is presented. It is then commented that a two plate arrangement would normally be utilized in two possible cases. One would be in the case of tanks, but since in the case of tanks utilizing homogenous armour of equal resistance and Approx. equal thickness, the main plate's resistance could not be raised relative to other plate to the point that VII>VI. The second case is the case of naval systems, were for example, there would be a realative thin plate in front of a main plate of perhaps cemented armour. In such case the ballistic resistance of the main plate was greater, in which case "VII can become greater than 1."

Elsewhere it is pointed out that the ballistic resistance of Wh with slightly greater tensile strength requires greater necessary velocity than standard. This would alter the constant from the standard. On Tirpitz the panzer deck was ~90kg/mm2 and the oberdeck was the naval standard 80kg/mm2. In this case the necessary V for the main plate is greater per unit thickness, raising c1h/c product to the point where VII>VI. This would mean that overall effective thickness was more than 100% the sum thickness in this case-not 88%

It is added that the values can be further increased by inclining the plates such that they are not exactly parallel.

The convention that two plates systems will not match the resistance of a single plate of equal sum thickness in many cases is not the case in all cases.

[JtD]

So to get from 660 to 720 you're essentially looking at the relative tensile strengths and estimate that number on your own, is that right? It's not from any report that is directly linked to Krupp armour penetration tests.

It should be noted that the C=660 for homogeneous armour in the report refer to "Wh", i.e. the Bismarck class main deck material, but then this is about the relative qualities and it doesn't matter if it's 660/720 or 605/660.

Once more to the formula that needs to be greater than one in order to make a two plate arrangement more effective than a single plate arrangement, and feel free to try that out in the Excel sheet I provided:

The equivalent single plate thickness depends on the qualities of the plates involved, their resistance to being penetrated. For instance, if you have soft homogeneous armour in front of a cemented plate, decap the shell with the first plate and have awful penetration capabilities against the cemented plate without a cap, you may have (example from report)
C1h = 680
C2 = 900
Furthermore, if you're able to make a superb thin homogeneous plate, but cannot manufacture a thick plate to the same standard, the value of C would be going down for the reference, which is a plate that is as thick as both the above plates together. No value is given in the report, but lets say
C = 600

Now the formula can compare the relative merits of the systems:
a) a thin high quality homogeneous plate in front + a thin high quality cemented plate behind it
b) a single thick medium quality homogeneous plate as reference

Lets assume a front plate of 80mm, backed up by 240mm and see what's the equivalent single plate thickness, using the C values from above, and we find that the plate combination results in a whopping 422mm medium quality homogeneous plate equivalent!

Now why is it that much more? Because we have to penetrate 240mm of cemented armour with a decapped shell and the reference is homogeneous, medium quality armour that will attacked by a capped shell.
The same arrangement, but with all amours of same quality, say all homogeneous with no manufacturing problems for thicker plates (C1h = C2 = C), the system is giving only an equivalent of 265mm single plate thickness.
So all this means:
a) If the first plate can manage to influence the shell in a way that significantly increases C2 (only way is to decap a shell then hitting cemented armour), then it is worth it.
b) If you cannot manufacture thick plates of decent quality, two plates might be better.

Now look a the Bismarcks deck system, two homogeneous decks of slightly different quality. I'll just stick with 660/720 given by Dave Saxton, personally I'm sceptical of these figures, but that not now. I'm not decreasing the quality of the thick equivalent single plate, so
C1h = 660
C2 = 720
C = 660

This gives:
50 + 80 -> 110 mm
50 + 95 -> 125 mm

It should be noted that, if a single plate of C = 720 quality was to be used, you'd only need 99mm and 112mm respectively.

I hope this was clear enough and easy enough to understand. It is not correct that Gercke gives an equivalent single plate thickness of > 1 for the Bismarck class horizontal protection. It is correct that there are configuration where two plates give higher resistance than a single plate of the same total thickness.

[Dave Saxton]

Lets assume a front plate of 80mm, backed up by 240mm and see what's the equivalent single plate thickness, using the C values from above, and we find that the plate combination results in a whopping 422mm medium quality homogeneous plate equivalent!

Now why is it that much more? Because we have to penetrate 240mm of cemented armour with a decapped shell and the reference is homogeneous, medium quality armour that will attacked by a capped shell.
The same arrangement, but with all amours of same quality, say all homogeneous with no manufacturing problems for thicker plates (C1h = C2 = C), the system is giving only an equivalent of 265mm single plate thickness.
So all this means:
a) If the first plate can manage to influence the shell in a way that significantly increases C2 (only way is to decap a shell then hitting cemented armour), then it is worth it.
b) If you cannot manufacture thick plates of decent quality, two plates might be better...................

I hope this was clear enough and easy enough to understand. It is not correct that Gercke gives an equivalent single plate thickness of > 1 for the Bismarck class horizontal protection. It is correct that there are configuration where two plates give higher resistance than a single plate of the same total thickness.

Now your starting to get it! The first plate, utilized in a naval system of sufficient depth, does indeed influence the shell in way that it significantly increases C2.

*The panzer deck would always deal with de-capped shells. The most difficult shells to de-cap are shells with a sharper head shape. The British found in their post war testing that such a system with a 50mm upper plate always de-caps even shells with a 1.4 caliber radius head shape. It is stated that the necessary velocity is significantly greater for a de-capped shell than for a capped shell of equal mass, if the tensile strength of an homogenous plate is greater than 80kg/mm2. This will create the condition of VII>VI. Moreover the de-capped shell will not be of the same mass after the cap is removed. This will create an additional condition that increases C2 relative to C. In the Kratz paper he states that when using a methodology of examining one plate at a time that the removal of the cap and change in mass must be taken into account along with the striking angle and the energy reduction, but such methodology would only be useful if there are no nutation and precession.

*The behavour of the shell is altered by the upper plate such that there is nutation and precession. This always requires a significant increase in necessary V compared to no nutation or precession. An additional condition of VII>VI is realized. Moreover nutation and precession nullifies the advatanges gained by a blunt head shape. C2 is further increased relative to C.

* The velocity of the shell is reduced. It does not need to be reduced a large value to be significant because of the marked velocity effect observed of Wh. This factor is in addition to the greater necessary V of Wh at 90kg/mm2 compared to 80kg/mm2. The reduction of V further improves C2 relative to C.

[Dave Saxton]

b) If you cannot manufacture thick plates of decent quality, two plates might be better.

Nobody can. This is an untractable problem that US Naval research lab found there was no solution to. ADM213 points out that thinner plates were of higher quality relative to thicker plates per unit thickness (C2>C). If the overall shear strength can be comparable to a thicker section thickness, using two plates would be better indeed.

This speaks to some of the fundamental metalurgical properties unique to a material like Wh. Shear strength is increased by increased tensile strength, because shear strength is a % of tensile strength. Wh has more gradual reduction in ductility per increase in tensile strength through the range of hardness suitable for naval armour. Thus increasing the tensile strength can be of significant ballistic effect, with negligable influence on ductility- with Wh. BTW, it is spoken to in the document that increased tensile strength usually results in increased necessary V through the range of hardeness considered suitable for naval armour.

It is not correct that Gercke gives an equivalent single plate thickness of > 1 for the Bismarck class horizontal protection

He may not have mentioned the Bismarck by name, or provided an example specific to it, but the principles spoken to throughout, apply to the Bismarck's deck system very well. Mathematical short comings aside; the core observation that Bismarck's design results in an single plate equivalent of >1 stands.

[JtD]

This is getting tiring. You have the Excel sheet, so play with the numbers. And if you don't trust it, do your own calculations. When you do, pay big attention to the various C's, as you keep mixing them up. They are very clearly spelled out in the transcription of the Gercke interview, so there's no reason for you to continuously substitute (C2/C1h)^2 for (C1h/C). As soon as you apply them properly, you will get the same results the Excel sheet shows and I posted here. Bismarck did not have a physics defying, magic armour.

And, getting back to my original point, the quality of Richelieus horizontal protection is not worse than Bismarcks. The cemented armour comes with pros and cons, and so do the different layouts. Eventually, the horizontal protection is nothing that makes Bismarck "more powerful" than Richelieu.

Now the next point, iIrc correctly, was that a single hit could take out 50% of the main armament. Obviously, the chances for this happening to Richelieu are considerably higher than the chances for this happening to Bismarck. However, from any direction where both ships could bring 8 guns to bear, the target area for the main armament is much bigger on Bismarck, meaning a hit to one turret more likely. I think that this is even true when Bismarck is down to 3 turrets. So while Richelieu is clearly putting a lot of eggs into one basket, the risk of losing a portion of the main armament is much higher on Bismarck.

[Dave Saxton]

I'll simply remind you of some key points you wrote:

The equivalent single plate thickness depends on the qualities of the plates involved, their resistance to being penetrated. ..

a) If the first plate can manage to influence the shell in a way that significantly increases C2 (only way is to decap a shell then hitting cemented armour), then it is worth it.
b) If you cannot manufacture thick plates of decent quality, two plates might be better....
.

I have addressed these issues, but you apparently disregard that. You must take into account such factors as de-capping, nutation, precession, and the metalurgical variables and so forth in order to have numbers that mean anything.

Richs horizontal protection proved to be about 120mm-124mm effective.

[JtD]

You said C2 = 720, and that's what I used. If you need it to be it a 1000 now because 720 doesn't cut it, feel free, the Excel sheet will give you the result in no time.

Richelieus cemented deck was far more effective against bombs or projectiles coming in at really steep angles than it was at defeating shells coming in at shallow trajectories. It's wrong to make a judgement on the equivalent thickness based on a single shell hit. Someone who tries to lecture on metallic properties should know.

[Dave Saxton]

It's not a matter of picking a number to attain a result, but a matter of determining what values accurately reflects the effects of de-capping, nutation, precession, velocity reduction, tensile strength, ductility, shear strength ....and so forth... and the resulting increase of the panzer deck's resistance to penetration above standard.

Did Rich actually use cemented armour for its main armoured deck or was it just turret roofs? If so, this was a rather poor choice, because the AoF of fall of even extreme range shell fire results in striking angles that are still rather oblique.

[JtD]

So, it's not 720 then?

The French chose the armour to protect the ship against bombs, mainly, not long range shell fire. Thanks for asking about the deck, indeed it appears to have been non cemented, with the turret roofs being different. Sorry.

[JtD]

http://www.combinedfleet.com/okun_biz.htm

Ever read through this?

[RF]

This is a very long and technical report with some open ended conclusions, it doesn't really answer the question, was Bismarck the best?

[alecsandros]

This is a very long and technical report with some open ended conclusions, it doesn't really answer the question, was Bismarck the best?

Not to mention some of the arguments are faulty, while some important aspects are missing altogether. In the decade passed since it was written, many documents have surfaced, that change quite a bit the perspective on German armor.

[Some examples: Mr Okun considers Whotan as having 20% EL, while several German documents depict it at 23% EL, even at close to 80kg/mm2. In the same paper, the term "yaw" is used with a different meaning than US and German pre -1940 tests had. The consequence is that aspects such as nutation or precession are left out. The de-caping qualities of the forward and aft tranverse armored bulkheads are ignored (in the section covering the protection against shells coming from directly fw or aft of the ship). ]

Cheers,
Alex

[JtD]

This is a very long and technical report with some open ended conclusions, it doesn't really answer the question, was Bismarck the best?

It's a detailed analysis of the strengths and weaknesses of Bismarcks armour protection. And while I don't agree with every conclusion reached, it quite well illustrates why the horizontal protection was not the magic stuff some people on this board believe it to be.

[lwd]

some thougts on effectivenes of spaced armor according GB and US reports.

AD A954 865 Spaced Armor 1950.JPG

decapping gb.JPG

These pages seem to say:
1) If you can break up an AP shell with the first plate a second plate has a good chance of preventing penetration
2) If you decap a projectile it won't penetrate as well.
Nothing particularly new that I can see.

http://www.bismarck-class.dk/miscellane ... n_1946.zip

This is quite interesting. It'll take me a bit to digest it. More later.

related material on dtic.mil
http://www.dtic.mil/srch/search?searchv ... zation=YES

What material did you think was related? Most I saw dealt with modern composites and materials and/or long rod penetrators.

After viewing Thorsten's links I wonder how on Earth is somebody going to base his calculations with the navweaps and it's supporters material... it's clearly unaccurate.

...The de-caping qualities of the forward and aft tranverse armored bulkheads are ignored (in the section covering the protection against shells coming from directly fw or aft of the ship). ...

And how important do you think these woud be and why?

[Dave Saxton]

So, it's not 720 then?

Well I don't know. That is what it could be based on the tensile strength's effect on energy consumption alone, but it does not take into account such effects as de-capping, yaw, and velocity reduction.....ect... How much would numbers need to be altered to accurately reflect that? Another way to perhaps bring these factors into the equation is that factors that cause greater necessary V are tantamount to increasing the effective thickness of the main plate. However, it would have to be accurately quantified. Either way, we must use correct values or running the numbers means nothing. I'm interested in the truth, not in being an apologist or an anti-apologist.

I do know that an effective thickness of 4 1/2 -5 -inches is not consistent with other evidence of such a system. If we disregard the effect of yaw caused by the upper yaw plate on the USN system and apply this equation as is to the USN deck protection we won't come anywhere close to traditionally accepted values or calculated IZs. In some of the British postwar projectile tests (APP# 30) where they tested against a full scale system based on Tirpitz they found that the effects of de-capping were very significant. The system essentially defeated BB caliber shells at long ranges, even though it was not constructed with the correct interspace. In another test to see how much the penetrability of a shell was reduced by de-capping alone (but divorced from the effects of yaw) they fired uncapped 14" shells at a 100mm homogenous plates striking at 65* from the normal. It required velocities greater than 466 M/s to attain penetration. This is a greater Vnot than the initial striking V of a KGV 14" shell before it penetrates the upper deck at those ranges. It raises the question of if a KGV 14" could defeat the system.

Several of the British tests revealed their BB caliber shells did not penetrate more than 5-inches single plate deck protection at any range less than 32,000 yards. Moreover, the theoretical results from deMarre type models don't provide more than ~5-6 -inches of single plate deck penetration at striking angles 60* from the normal for wide range of bb caliber shells, and such models overstate penetration at such striking angles. Nominally 5- inches effective deck protection, is enough in most cases to provide the typical WWII IZ requirements. 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.