Bismarck and her contemporaries

[Bgile]

As near as I can tell, the 145mm side armor above the main belt was wasted as far as facing another battleship was concerned. When comparing armor weight that should be taken into consideration.

If the 50mm upper deck was capable of preventing shells from hitting the main armor deck, why was a main armor deck included at all? If the Germans designers really thought that would happen, why not just make a splinter MAD and save a lot of armor weight?

[alecsandros]

If the 50mm upper deck was capable of preventing shells from hitting the main armor deck, why was a main armor deck included at all? If the Germans designers really thought that would happen, why not just make a splinter MAD and save a lot of armor weight?

There are various reasons behind the multi-layered design of the deck (space array), and don't concern just stoping incoming shells, but also stability issues (the distribution of weight within the ship alters the centre of gravity and of bouyancy).

In regard to stoping heavy shells, the first layer of deck was known to be to thin to stop BB shells at most angles. It's scope was to render the shell ineffective, by either initiating the fuse (and a subsequent blast somewhere between the upper and lower armored deck) or, better yet, to decap it (and let it to rest somewhere between the decks, or, in a worst case scenario, below the second armor deck. Anyway, with low risk).

Besides the obvious effects described above, the upper deck's intention was also to alter the speed, mass (by decaping) and trajectory, and consequently kinetical energy of the shell, that would make it much harder to pierce the second skin.

All the best,

[Karl Heidenreich]

dunmuro:

Armour weight calculations are problematic. Direct comparisons are always difficult because each navy used different methods of weight calculation. For example some navies would include protective plating such as STS steel as armour, while others would include it as hull weight. Here's a comparison of KGV and NC done using the same methods of calculation:

http://en.wikipedia.org/wiki/Comparison ... h_Carolina

It is highly unlikely that Littorio carries more armour than KGV, for example, as Littorio's main belt is only about 4 metres deep versus 7 metres for KGV and while her turrets and barbettes are thicker, these are small in area compared to the main belt.

KGV's upper deck is 30mm and there is an additional 38mm splinter deck directly over the magazines.

I concurr that it´s difficult because of the stated reasons. I believe that R&R are quite clear that the overall weight of the armor scheme of the South Dakota Class do not surpass some 8,000 tons but in this reference goes as twice as that.

[Karl Heidenreich]

Bgile:

If the 50mm upper deck was capable of preventing shells from hitting the main armor deck, why was a main armor deck included at all? If the Germans designers really thought that would happen, why not just make a splinter MAD and save a lot of armor weight?

The existence and purpose of that upper deck has been confirmed by three reliable sources now: G&D, the Baron and Breyer. I think that discussion must go in the direction of it´s real performance.

[Karl Heidenreich]

It has been brought to my attention that Bismarck´s main guns were 15" L/42 instead of L/47. Because my main source, this time, was G&D I used the information contained in it, but I was aware, then and now, that the main guns were L/52.

Do someone has an explanation for this discrepancy?

[Thorsten Wahl]

acoording Navweaps

Gunlength 19.630 mm ->52xcaliberlength
borelenght 18.405 mm ->48xcaliberlength
riflinglength 15.982 mm->42xcaliberlength

The 47 caliber thing is unclear in the sense of definition

citadelarmor (145mm) and maindeckarmor(50/80mm) was intended to keep multipurpose bombs up to 500 kg and small-caliber-shells completly outside of the ship.
maindeckarmor was also intend to fuze incoming maincaliber shells and small AP Bombs before they hit the armored deck

the citadelarmor also partly gives the mainarmordeck additional protection from incoming oblique attacks of main calibers
depending from the angle of incoming shells there were up to 40% of the armored deck area additional protected in this way
by the way the around 4,5 - 5,65 m of scarp on both sides were completly impenetrable by any shell

[Thorsten Wahl]

by the way the around 4,5 - 5,65 m of scarp on both sides were completly impenetrable by any shell

additional i forgot
impenetrable at obliqe attacks

[José M. Rico]

Bismarck upper deck over magazines is 80 mm not 50 mm

I don’t think so. The revised B.B.V. (special design specification) contains still no reference to it. There is just an 80 mm plating around the MA turrets II and III mentioned. In case of Bismarck the armour deck - at least around turret C and D - was definitely increased up to 100 mm.

Herr Nilsson is correct. The upper deck was 50mm overall except for some parts around the secondary turrets where it was 80 mm because below there were secondary magazines for the AA battery. However, the bolted joints on the upper deck where the 50mm plates superimposed were 80 mm too. See attached drawing (the darker lines are 80mm):

[lwd]

...In regard to stoping heavy shells, the first layer of deck was known to be to thin to stop BB shells at most angles. It's scope was to render the shell ineffective, by either initiating the fuse (and a subsequent blast somewhere between the upper and lower armored deck) or, better yet, to decap it (and let it to rest somewhere between the decks, or, in a worst case scenario, below the second armor deck. Anyway, with low risk).

Besides the obvious effects described above, the upper deck's intention was also to alter the speed, mass (by decaping) and trajectory, and consequently kinetical energy of the shell, that would make it much harder to pierce the second skin. ...

On decapping - do you have any evidence that this was actually one of the reasons for the desing? When this has come up before the Italians are the only ones where it's been documented that decapping was one of the aims of the armor array.

On changing trajectories - Shells tend to deflect toward a normal line through the armor so an upper deck is actually going to alter the trajectory in a direction such that it's more likely to penetrate a lower deck.

On fuse initiation - Note that this only works for some fuzes. US BBs were desinged to intiate bomb fuzes. The above may have worked on some of the faster fuzes (I beleive the British fuzes were such) but wouldn't have provided any benefit vs US or Japanese fuzes. Not sure what the status of French or Italians in this regard.

[alecsandros]

On decapping - do you have any evidence that this was actually one of the reasons for the desing? When this has come up before the Italians are the only ones where it's been documented that decapping was one of the aims of the armor array.

I have no primary docs as to prove this. However, I don't think it was that difficult for the designers to figure it out - it's XIth grade physics.

On changing trajectories - Shells tend to deflect toward a normal line through the armor so an upper deck is actually going to alter the trajectory in a direction such that it's more likely to penetrate a lower deck.

If that's the case, indeed it would not be ok. Do you have some studies about shell behavior after penetration? I'd be very interested in them.
I think that piercing the first skin would anyway decrease the speed significantly and make the shell harder to pierce the second one.

On fuse initiation - Note that this only works for some fuzes. US BBs were desinged to intiate bomb fuzes. The above may have worked on some of the faster fuzes (I beleive the British fuzes were such) but wouldn't have provided any benefit vs US or Japanese fuzes. Not sure what the status of French or Italians in this regard.

It's difficult to speculate that the German engineers had hard data about the other navies actual ballistic performance. Defusing is by any means one possible consequence of a shell penetrating an armoured deck.

Cheers,

[lwd]

On decapping - do you have any evidence that this was actually one of the reasons for the desing? When this has come up before the Italians are the only ones where it's been documented that decapping was one of the aims of the armor array.

I have no primary docs as to prove this. However, I don't think it was that difficult for the designers to figure it out - it's XIth grade physics.

Actually it's not. Read the articles on it at the navweapons site. The Italians apparently ran explicit experiments and desinged the VVs belt armor to decap. It's not just a matter of the steel thickness but spacing and such and in some cases decapping has minimal effect.

On changing trajectories - Shells tend to deflect toward a normal line through the armor so an upper deck is actually going to alter the trajectory in a direction such that it's more likely to penetrate a lower deck.

If that's the case, indeed it would not be ok. Do you have some studies about shell behavior after penetration? I'd be very interested in them.
I think that piercing the first skin would anyway decrease the speed significantly and make the shell harder to pierce the second one.

No refernces at hand but it's been mentioned in a number of meetings I've attended and what more makes sense if you consider things like line of least resistence and the actual mechanics. The velocity loss also might not be as much as you think again note that in the absence of decapping 2 plates are easier to pentrate than a single plate of the same thickness. Again there's an articcle on this on the navweapons site.

On fuse initiation - Note that this only works for some fuzes. US BBs were desinged to intiate bomb fuzes. The above may have worked on some of the faster fuzes (I beleive the British fuzes were such) but wouldn't have provided any benefit vs US or Japanese fuzes. Not sure what the status of French or Italians in this regard.

It's difficult to speculate that the German engineers had hard data about the other navies actual ballistic performance. Defusing is by any means one possible consequence of a shell penetrating an armoured deck.

Cheers,

The question is whether it was a desing feature or not. Like I said the US designed the upper armored deck to initiate bomb fuzes. Did the Germans do the same or did they desing them to intiate shell fuzes?

[Dave Saxton]

The Germans generally disallowed the mass reduction factor of de-capping from their IZ calaculations, but in the case of barbets and the scarp triangle, the principles of de-capping's critical velocity were considered.


According to US National Lab studies, the trajectory change toward the normal is on the order of 1 1/4 degrees (assuming there is 0 yaw at impact) were the thickness of the armour plate is 80% the diameter of the projectile. There are other complexities involved though such as yaw at impact, and the tensile strength of the armour material as well as it's thickness.


The fuze delay of American APC was 0.035 seconds. Muir reports that it was typically 0.033 sec in practice. This will be viable out to about 25,000 meters (27,400 yards) range in the case of the 16"/45 gun and factoring in a 50mm Wh upper deck.

There were numerious independent studies commisioned that quantified the amount of V reduction of the upper deck.

[Dave Saxton]

Bismarck upper deck over magazines is 80 mm not 50 mm

I don’t think so. The revised B.B.V. (special design specification) contains still no reference to it. There is just an 80 mm plating around the MA turrets II and III mentioned. In case of Bismarck the armour deck - at least around turret C and D - was definitely increased up to 100 mm.

Herr Nilsson is correct. The upper deck was 50mm overall except for some parts around the secondary turrets where it was 80 mm because below there were secondary magazines for the AA battery. However, the bolted joints on the upper deck where the 50mm plates superimposed were 80 mm too. See attached drawing (the darker lines are 80mm):

This is still unclear, because the Norwegian salvage firm that scrapped the Tirpitz reported that the upper deck was 80mm over the magazines as built.

[alecsandros]

Though it would be interesting to have an academic answer to the question of "was it a design feature or not", the system worked quite well during Tirpitz's bombings. Also, all the analyses that I've read so far (books, online data such as Nathan Okun's analysis) concur to the above stated generic characteristics of space array armor.

Excerpt from Navweapons:
"Armor penetration requires a rather lot of information, but decapping of the projectile by breaking the rather weak solder and/or mechanical bond between the nose and cap base is VERY, VERY SIMPLE:

(1) 0.08-0.08049-caliber thickness of ANY KIND OF HOMOGENEOUS IRON OR STEEL PLATE has a 50% chance of decapping ANY KIND of capped projectile over 40mm in diameter under ANY impact condition, penetrating or not.

(2) 0.0805-caliber and up thickness ALWAYS decaps the projectile, penetrating or not.

" (N. Okun)

Also, I don't see where you are going with the "bomb versus shell", as they were both significant dangers in WW2, and it is very hard to find an armour that would work well against bombs and very poorly against shells.

Cheers

[Karl Heidenreich]

José:

Herr Nilsson is correct. The upper deck was 50mm overall except for some parts around the secondary turrets where it was 80 mm because below there were secondary magazines for the AA battery. However, the bolted joints on the upper deck where the 50mm plates superimposed were 80 mm too. See attached drawing (the darker lines are 80mm):

That´s in agreement with G&D information and with the specs that this website shows.

Best regards,