Bismarck class turret protection

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Dave Saxton
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Bismarck class turret protection

Postby Dave Saxton » Tue Oct 17, 2006 3:52 am

The heavy battery turret protection of the Bismarck class is ofton maligned. I have been rather critical myself. Recent disscusions about turret protection of other battleships led me to look into the Bismarck class turret armour in greater detail, and the results are surprizing.

First, looking at the face plate, at 360mm it's slightly thicker than British practice, but not as thick as American practice. Using the Krupp penetration curves for the German 15-inch vs KC armour it looks like the face plate provides protection vs high velocity 15-inch guns beyond 21,200 meters, or about where the impact velocity falls below 500m/s.

The roof plates were 130mm WhnA. Using German curves for homogenous armour, the roof plates provide protection against the German 15-inch out to 30,000 meters. The French and Italian 15-inch guns eventually got more deck penetration, but not untill well beyond 30,000 meters. The German 15-inch gun actually has more deck penetration out to 30,000 meters. The British 15-inch is near it's maximum range, so it has a steeper angle of fall. This means the British 15-inch has deck penetration more typical of a 16-inch gun, from 25,000 meters to 30,000 meters, and can penetrate the roof plates by 28,000 meters.

The inexplicable 180mm angled facets are just that, if we take for granted that they are only laid back 30* I have taken this for granted for years now, but breaking out the protractor reveals that they were actually laid back 66*! By calculating the striking angle and velocity data into the curves, it looks like the angled facets actually work, vs 15-inch guns, out to about 30km battle ranges.

The Bismarck class turret protection is very good vs 15-inch guns between 20,000 and 30,000 meters. Additionally, the Nelson class 16-inch is actually less powerful than the European 15-inch guns. It looks like the Bismarck class heavy battery protection isn't that bad after all.

I have been about as critical as anybody when it comes to the turret protection of the Bismarck class, and well understand the critical views ofton expressed.

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Postby RF » Tue Oct 17, 2006 7:25 am

One key point that needs to be looked at in a discussion like this is the actual impact of shell hits on Bismarcks' turrets.
On the final battle of 27 May an early hit from Rodney at a range where it is claimed Bismarcks' turrets had good protection from 16 inch shells put both Anton and Bruno out of action, ie. took out half of Bismarcks main armament, as well as sending a sheet of flame and shrapnel right up the command tower. This one hit effectively turned what would have been a battle into a target practice session for Rodney and KGV.
Seems to me the turret protection wasn't as good as claimed.

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Postby Dave Saxton » Tue Oct 17, 2006 3:36 pm

We don't know what really happened there. The turrets are buried in the mud and nobody knows if there are any full penetrations, or if there are, when they occured, as far as I know. At what range did the Rodney hit(s) occur? Several minutes transpired before the pivitol hit occured. It may well have been short of the turret/barbet IZ by that point. If Rodney opened fire at 25,000 yards, that's only a few thousand meters beyond 20,000 meters.

As was pointed out in the disscussion on the Iowa face plate, a full pentration need not occur to fully or partially disable a turret. In light of analyzing this anew, I see no reason to say Bismarck's heavy battery protection was any worse than any contemporaries against guns of it's own caliber, at reasonable ranges.

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Postby RF » Wed Oct 18, 2006 8:47 am

Dave Saxton wrote:We don't know what really happened there. The turrets are buried in the mud and nobody knows if there are any full penetrations, or if there are, when they occured, as far as I know. At what range did the Rodney hit(s) occur? Several minutes transpired before the pivitol hit occured. It may well have been short of the turret/barbet IZ by that point. If Rodney opened fire at 25,000 yards, that's only a few thousand meters beyond 20,000 meters.

As was pointed out in the disscussion on the Iowa face plate, a full pentration need not occur to fully or partially disable a turret. In light of analyzing this anew, I see no reason to say Bismarck's heavy battery protection was any worse than any contemporaries against guns of it's own caliber, at reasonable ranges.


My understanding was that this hit was at the back of one of these turrets and the British observers ''saw the roof of B turret blow off'' and it apparently KO'd both forward turrets.
The analysis by Ballard et al, focussed on the impact of this hit on Bismarck's command positions and armoured tower, not on the gun turrets themselves. I think this still remains an unknown.
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Postby Tiornu » Wed Oct 18, 2006 9:29 am

There is no way that Bismarck's turret protection--with no immunity to the British 14in gun, the weakest gun of the treaty designs--can be labeled anything but lame.

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Postby Dave Saxton » Wed Oct 18, 2006 3:31 pm

I'm just doing the math. Using primary penetration data and applying the numbers, it looks like the turrets had an IZ from roughly 20km to 30km, vs 15-inch. How could they have no immunity at all vs 14-inch?

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Postby Dave Saxton » Wed Oct 18, 2006 3:41 pm

RF wrote:My understanding was that this hit was at the back of one of these turrets and the British observers ''saw the roof of B turret blow off'' and it apparently KO'd both forward turrets.
The analysis by Ballard et al, focussed on the impact of this hit on Bismarck's command positions and armoured tower, not on the gun turrets themselves. I think this still remains an unknown.

Yes, the state of the turrets themselves remain an unknown. It's my understanding that the observance of debris (back plates) blowing off Bruno occured late, at very short range. This wasn't the early hit as I understand it, but even the earlier hit probably occured at ranges of less than 20k. Anton may have come back on line later on. I don't know what happened there with any degree of certianty, and I don't want to speculate too much. I would much rather go with the numbers.

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Postby Karl Heidenreich » Wed Oct 18, 2006 6:30 pm

Dave Saxton:

The Bismarck class turret protection is very good vs 15-inch guns between 20,000 and 30,000 meters. Additionally, the Nelson class 16-inch is actually less powerful than the European 15-inch guns. It looks like the Bismarck class heavy battery protection isn't that bad after all.



If I can remember this was discussed before (I can´t find the thread after looking quite a while), specially about the impact force of Nelson´s 16" and the conclusion was that Nelson´s wasn´t that powerfull if compared with USN shells or with the German 15".
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Postby tommy303 » Wed Oct 18, 2006 7:33 pm

The hit which initially disabled Turret B and the presumed hit which caused an internal explosion were two different events separated by a considerable time element. The first may well have been a shell which struck and holed the barbett at its top edge which jammed the turret and effectively put it out of action. It is doubtful that the hit also put Turret A out of action. I consider it more likely that Turret A was either hit by a shell which was not spotted from the British ships or suffered a mechanical problem completely independent of what happened to Turret B. Whatever the cause, it appears the damage was only temporary as Turret A seems to have come back on line after about 20 minutes for at least one more salvo before being knocked out for good.

The actual logic behind the armouring of the turrets themselves seems to have been based more on expediency than on ballistical data. If one looks at the interior of the gun platform, bearing in mind the placement of the guns, trunnions, hoist, turret rangefinder, gun loading cage and rammer arrangements, one can see that what the Germans did was similar to placing a rectangular box around the platform, and par away the upper edges where there was nothing to protect but air. Since you don't want to waste armour and weight protecting empty space, you cut away those areas where there is no equipment to protect, and slope the armour up to the remaining portions of the turret crown.

There is little question that the sloped armour could be made thinner than the vertical armour and still offer similar resistance, but here the Germans seem to have fallen short a bit. This was most likely because of decisions made at the top to up gun the ships to 38cm and still keep them within a certain weight and size limit. The multiple changes in design and armament during the actual planning and building stages resulted in compromises which were not always beneficial.

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Postby Dave Saxton » Wed Oct 18, 2006 8:27 pm

Hi Thomas,
By crunching the numbers it appears that the slope angle and the thickness of the sloped back upper crowns were derived at by careful calculations of ballistic data.

At 20,000 meters range, the 15-inch projectile strikes at ~510m/s with an striking angle of 50* against the sloped back surface. The penetration of homogenous armour is about 175mm. At increasing range; the striking velocity and the striking angle both gradually change, keeping penetration at about 175mm out to about 30km.

Bismarck's list to port may have been detrimental if any of the turret crowns were hit directly from that side during Bismarck's the final battle, though.

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Postby tommy303 » Wed Oct 18, 2006 8:46 pm

Hi Dave,

I am not so sure the slope at the rear was anything more than there being little high up in the turret rear until you reached the rangefinder, and the need for more weight in back to keep the turret in balance. The combination of a longer shallower slope and heavier armour might make it appear to be have been a careful calculation, but then one would have to ask why the turret rear when logic would say it should have been the turret front that needed the attention most.

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Postby Tiornu » Wed Oct 18, 2006 9:17 pm

How could they have no immunity at all vs 14-inch?

The shell can hole the faceplate from about 28,000 yards. It can defeat the flat roof from about 30,000 yards. As far as I know, the angled facet is not secure at any range. What definition of "penetration" are you using?

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Postby Tiornu » Wed Oct 18, 2006 9:19 pm

Tommy, I believe "sloped back" is meant to have a hyphen.

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Postby José M. Rico » Wed Oct 18, 2006 10:36 pm

Tiornu wrote:
How could they have no immunity at all vs 14-inch?

The shell can hole the faceplate from about 28,000 yards.

A British 14-inch AP shell penetrating 360 mm of KC armor from 28,000 yards? :think: According to the following tables (see link) the range should be reduced to 15,000 yards in order to have any chance to penetrate a plate of that thickness.

http://navweaps.com/Weapons/WNBR_14-45_mk7.htm

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Postby tommy303 » Wed Oct 18, 2006 11:23 pm

Hi Tiornu,

you are probably correct about sloped-back.

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