Bismarck and her contemporaries

[Dave Saxton]

Without a detailed read I would hazard a guess that the Bismark's array falls short due to the 145mm upper belt or cathedral armour in the opinion of your quoted post last?

... her contemporaries had exactly 0mm upper belt.

Exactly. The upper belt of BS and TP was considered a great asset, not a weakness, and a big improvement on Scharnhorst.

[sineatimorar]

Excuse me for maybe been a doofus. But what in the world is BS & TP ?

[Dave Saxton]

BS = Bismarck
TP= Tirpitz
SH= Scharnhorst
GU= Gneisenau
SC= Scheer
LW= Luetzow
PG= Prinz Eugen...and so forth...

[sineatimorar]

Oh! Ta. Love the shorthand.

[alecsandros]

Hello,
After the work with the horizontal protection of contemporary battleships, I started working on the level of lateral protection of the magazines.

Here is the snapshot of the work...

[dunmunro]

Hello,
After the work with the horizontal protection of contemporary battleships, I started working on the level of lateral protection of the magazines.

Here is the snapshot of the work...

I think you'll find that the 5in magazines on North Carolina, South Dakota and Iowa could be penetrated by a direct hit through the main belt, as they are located amidships, directly under the main armoured deck, which is one deck higher than the main magazines.

Total armour to be penetrated to reach KGV's magazines would be the main belt + backing, two thin bulkheads, a 1.75in (2 x 22mm D steel) bulkhead, and then a 1.5in D steel bulkhead around the magazine.

[alecsandros]

Total armour to be penetrated to reach KGV's magazines would be the main belt + backing, two thin bulkheads, a 1.75in (2 x 22mm D steel) bulkhead, and then a 1.5in D steel bulkhead around the magazine.

...
I had the figure of a 38mm bulkhead (2x19mm). Using the sqrt formula, that equates to ~ 27mm single sheet. If it was 44mm (2x22), than the corresponding thickness would be 31mm.

[alecsandros]

I think you'll find that the 5in magazines on North Carolina, South Dakota and Iowa could be penetrated by a direct hit through the main belt,

It's very possible, as you say - and that would have been a serious hazard.

But the table concerns the main magazines, which AFAIK were lower in the ship(s).

[sineatimorar]

If I may you are assuming that GK-DOS 100 document is accurate if it's assumptions on foreign battleships particulars. I believe that there is serious questions of accuracy as the penetration curves were infact based on assumptions. Looking at the figures in column titled Hell condition seems to to suggest that there would have been penetration at shorter range with ships with more armour?. For instance the Yamato figure is consistently less than other smaller thinner armoured types. The performance suggested of Japanese armour here is NOT reflective of performance found in post war USA tests on that armour.

Nor does the document consider sub surface hits that go under the protective layers. The dud shell that came to rest on the double bottom on P of W was still viable, if a long delay set fuse had not failed to activate it may well had exploded under the protective layers for the magazine. Correct me if I am wrong but the only ship in the list actual built with armour floor to it's magazine is the Yamato.

The doclument is seriously flawed in it assumptions of armour performance and the assumption that the only shell path is thru the protective layers.

[Alberto Virtuani]

Alecsandros wrote: "After the work with the horizontal protection of contemporary battleships, I started working on the level of lateral protection of the magazines"

Very interesting and complete work !

One question: when you imagine Tirpitz class penetration, are you assuming through the main belt and the slope (and not the flat armored deck), aren't you ?

I was thinking no hit could penetrate both at almost any distance, and I now wonder how BS was not blown up on May 27 when distances were very very short and a she received a deluge of heavy hits. Was it possibly related with the fact that BS was already quite low in the water and the slope couldn't be reached by a direct (above water) hit especially from the port side ?

Bye, Alberto

[alecsandros]

For instance the Yamato figure is consistently less than other smaller thinner armoured types. The performance suggested of Japanese armour here is NOT reflective of performance found in post war USA tests on that armour.

... Yamato main armor belt as 410mm thick, declined at 20*. It was the thickest armor belt ever assembled and it was declined at the steepest angle.

If you would take the time to read the document, you would find that the quality factor of the belt is 0.9, thus equivalent to a 369mm thick Krupp or British post-1930 CA. Using GKDOS curves for 369mm armor declined at 20*, one finds various intervals for perforations in heil and grenz condition.

[alecsandros]

One question: when you imagine Tirpitz class penetration, are you assuming through the main belt and the slope (and not the flat armored deck), aren't you ?

Yes, thorugh the main belt and then through the sloped section of the main armor deck, and also through the 45mm thick whotan torpedo bulkhead.
I know most sources tend to say that it was impossible for a given shell to perforate all armor systems. I also believe that , in most cases, the 315mm KC n/A + 100mm teak wood + 16mm St52 main belt, 120mm Whotan slope and 45mm TDS would block allmost any projectile. However, performance of APC shell was constantly improving, and the German 38cm L4.4 shell was a very good example of how dangerous the shells actualy became.

This is why I think that, at very short ranges, where angle of fall is very small, and velocity is very large (but not so large as to shatter the projectile on contact with heavy armor), the German 38cm APC shell had good chances of perforating the entire armor array and actualy reaching the main cartridge magazines, which were located directly below the main armor deck.

Here is how I envisaged it:
4km range, v0 = 820m/s. Impact velocity: 745m/s, angle of fall: 2*
Tirpitz main armor belt adjacent to the main magazines was declined at various angles (between 7* and 17*). The average declination was about 12*.
Thus, the angle of incidence between projectile and plate would have been 2+12* = 14*, assuming no lateral obliquity (ships at perfect alignement).

According to GKDOS-100 curves, a shell striking at 745m/s at a 14* angle would perforate about 664mm of KC n/A armor , and the shell would still be in undamaged and in effective condition ("heil").

Naturaly, the shell would be decaped by the armor belt, but it would still have an exit velocity of ~ 500m/s, a mass of ~ 660kg and it would exit at a ~ 12* angle from the plate normal.
Next, it would strike the 120mm main armor deck, sloped at 68*. Impact obliquity would be 68* - 12* = 56* from plate normal. A rather bad impact obliquity, isn't it ? BUT, this is the place were the German 38cm APC shell shows it's value: it performed very well in obliquities of up to 60*. MOreover, the thickness/diameter ratio would be 120/380 = 0.32, thus favoring the shell.
It's true Krupp studies showed that homogenous armor tended to stop decaped projectiles traveling at 300-400m/s, IF the thickenss/diameter ratio was at least 0.3. However, our shell travels at 500m/s.

Thus, my impression is that complete perforation of the 120mm armor slope would occur in this instance, and the shell would still retain at least 300m/s velocity. It may be damaged, but it would still be very dangerous. Exit angle may push the projectile rather down in the ship. But I don't think that would always be the case.

Then, the remaining 45mm of Whotan armor torpedo bulkhead would not change things - the shell would continue to move towards the magazines and would be very dangerous...

==
I don't know if this is the way it would happen, but this is what I think...
==
About the final hours of the Bismarck: there would be several explanations for no magazine detonations.
First of them would be , for me at least, insufficient development of 14" and 16" APC shells for oblique performance. Allmost certainly those types of shells did not have the capability of remaining in a fit state to burst after passing through the 120mm slope (if they would get that far).
Another factor would be real life obliquity. Thus, in my example above, the 38cm L4.4 shell would strike at 14* compounded obliquity. However, in real life perfectly parrallel courses and ship positions are almost impossible to obtain; ship motion on all 3 axes also modifies the obliquity. With Bismarck low in the water and a severe storm yawing and pitching all ships constantly, real obliquities on the face of the armor plates could have been dramaticaly bad, and many shells probably would not perforate not even the exernal 320mm armor belt.

Finaly, many shells were fired at extremely close range, giving them a rather high impact velocity. British shells of the period were not thermically treated to the same extent as the German ones were, and there were significant differences in hardness throughout the shell body. So some say there was the possibility of shell shatter on impact with heavy armor, as the forces exerted on the shell body at such speeds (> 700m/s) would destroy it before it could start perforating the armor.
This is very possible to have happened with some of Rodney's final salvos, that "exploded in contact with the aft sections of the ship [Bismarck]". How could APC shells explode in contact with armor ? They were supposed to perforate it, and then to explode...

These would be my points...
==
P.S: Many thanks for your kind words, Alberto, I hope this helps...

[sineatimorar]

So the data on armour performance has been standardized before been applied to the penetration curves using modern knowledge of historical armour performance and not the assumed knowledge of the orginal doclument ?
If so I withdraw my previous statement completely as been a incorrect assumption on my part.

If I may ask, what in your opinion, been the result of the dud shell hit on the P of W if infact it had not been dud? I have read opinions that to penetrate under the deeper belt the shell would have had to travel a distance and time period greater than the delay of a working fuse. Being that there was some reasonably bad weather at the time of the engagement, I wonder if the conditions could have effected this synopsis, and to what amount of rolling or pitching would have made it possible that a viable shell could have at least made it to hit the TPS of the P of W and explode?

By and by I applaud you if you have gone to the trouble of standardization of armour performance when carrying out any comparison as few bother to do so, thus giving as less than accurate conclusion to their work.

Having written the first part of this as you posted your last ,I have one other question. In your example given last did you factored in the fuse delay equalling the time left for the intact shell to penetrate past the first armour layer that would have activated the detonation process? It is clearly evident from historical records that dud shells defeated the spaced armour defenses.
I am not in anyway stating that you are in anyway in error, just that it not mentioned in your factoring of your example.

[alecsandros]

So the data on armour performance has been standardized before been applied to the penetration curves using modern knowledge of historical armour performance and not the assumed knowledge of the orginal doclument ?

Hello,
As I said, it is a rather subjective work.
I may have made a ton of errors...
But yes, I tried to use the documents and books available now, in 2013, and draw some conclusions.
Japanese thick armor plates yielded very inconsistent results during US testings. For instance, the 660mm thick armor plate which was intended for Shinano's main turrets (before she was converted to a carrier) proved exceptionaly good.
Only after attacking it from 1000 yards with the 16"/L50 gun coudl the plate be perforated (despite the fact that penetration formulas indicated the US gun could perforate that thickness at much larger range - about 10000 yards or more )

On the other hand, cruiser and battleship main belts had apparently less stopping power than their US counterparts.
So, who is right ? It's very difficult to know. I don't know for sure. I tried to make the best average I could think about...

Add to that the uncertainties of T/D , plate to plate variations, average brinell hardness of Cimentite in comparison to average hardness of the attacking shell perforating cap, and the problem becomes more and more dubious....

===

If I may ask, what in your opinion, been the result of the dud shell hit on the P of W if infact it had not been dud?

... AFAIK, the shell came to a halt after hiting Prince of WAles torpedo bulkhead, 38mm thick (or 44 ?). That is a rather thin piece of armor, so the shell must have had very low velocity. If , in some way, it could still explode, the damage done would have been local, with some flooding seen in the area. Most likely it would have been similar to the damage Bismarck suffered after the 14" shell from Prince of Wales exploded in contact with Bismarck's TDS - the battleship lost a boiler room due to flooding, but still retained maximum speed.

Being that there was some reasonably bad weather at the time of the engagement, I wonder if the conditions could have effected this synopsis, and to what amount of rolling or pitching would have made it possible that a viable shell could have at least made it to hit the TPS of the P of W and explode?

NOt only that, but large ships moving at high speeds (28kts+) tend to have less water around their mid-sections. IIRC, this is called a delta wave. The difference between normal sea level and the level of the water at mid-ship section can be up to 1 meter.
So yes, in that battle, with PoW doing 29kts, and turning violently several times, I think she could have been hit below her armored belt by a well-functioning 38cm APC shell. I don't know though if the 0.038 - 0.040 seconds fuze delay of the German shells would have been enough to let the shell get to the main magazines though...

In your example given last did you factored in the fuse delay equalling the time left for the intact shell to penetrate past the first armour layer that would have activated the detonation process?

Fuze delay for that shell was about 0.040 seconds, so even assuming 400m/s average velocity between first contact with the outer armor and final detonation, the sehll woudl still travel some ~ 16meters, enough to reach the main magazines.

===
However, stuff like projectile shatter during oblique impact (with the sloped armor), fuze blindness, or deflection at a bad exit angle from the slope can still save Tirpitz from a catastrophic explosion :)
BUT, in certain conditions, my opinion is that a 38cm L4.4 shell fired from a close distance, can be very dangerous even for this formidable space-array system. [And, as you pointed out, even a dud shell in the magazines can be extremely dangerous...]

Cheers, and thanks for your kind words; there is alot of work to be done still, and even so I still don't know if it would ever be enough... There are so many slippery problems...

[sineatimorar]

That is what so interesting about this subject in general. No matter how much study you put into it, how sound you are with your own conclusions, somebody can come up with a point that is so B.B.O. ( blindingly bloody obvious ) that you think to yourself one "why did I not see that? " and two " How does that effect my other conclusions?".

Don't you just love it ?