Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Discussions on all (non-biographical) aspects of the Kriegsmarine except those dealing with the U-Boat forces.
User avatar
Pips
Member
Posts: 1226
Joined: 26 Jun 2005 08:44
Location: Canberra, ACT, Australia

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by Pips » 14 Jun 2017 00:36

Terry Duncan wrote: They also thought the most likely engagement she would fight would be at close or medium ranges under North Sea conditions, for which she is a very good design indeed. For longer ranges, the design wastes a lot of weight, and whilst difficult to sink, is relatively easy to disable.
That is a fascinating comment Terry. Would really appreciate it if you could expand on it. Why (at close/medium) ranges was the Bismarck design so good? And at longer ranges less so?

I always thought the goal of a battleship gun battle to keep it at long range, so that plunging fire could cause the most penetration.

User avatar
Terry Duncan
Forum Staff
Posts: 6059
Joined: 13 Jun 2008 22:54
Location: Kent

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by Terry Duncan » 14 Jun 2017 13:21

Pips wrote:
Terry Duncan wrote: They also thought the most likely engagement she would fight would be at close or medium ranges under North Sea conditions, for which she is a very good design indeed. For longer ranges, the design wastes a lot of weight, and whilst difficult to sink, is relatively easy to disable.
That is a fascinating comment Terry. Would really appreciate it if you could expand on it. Why (at close/medium) ranges was the Bismarck design so good? And at longer ranges less so?

I always thought the goal of a battleship gun battle to keep it at long range, so that plunging fire could cause the most penetration.
Hi. No problem at all to expand on what I said. Bismarck was designed with engagements in the North Sea in mind like the WWI dreadnoughts where, due to the pollution and weather conditions, a visibility of much over 20,000 - 24,000 yards is seldom experienced, with average visibility distances in WWI being quoted at between 8,000 - 12,000 and 12,000 - 16000 yards. This means the angle a shell strikes the armour at is close to the perpendicular for verticle armour, depending on the ranges and shell velocity, but with the ranges quoted the shell will likely hit belt armour at 75 - 85 degrees, which makes for good penetration, whilst the same shell striking the deck with strike at 5 - 15 degrees and the armour will simply bounce the shell harmlessly away over or through the superstructure, which is really what happened to most deck hits at Jutland where the BC's had deck armour within 0.5" of that carried by the dreadnoughts, rather than the myth of 'thin deck armour' which as an excuse for not wanting to make public the removal of fire prevention equipment.

With that in mind, Bismarck carried the armour deck relatively low in the hull, at about the waterline level where it would also gain protection from the water as well as making it very difficult to hit with shells penetrating the belt. In turn, this allowed the belt to be thinned above the main deck thus saving weight. To give greater protection to the deck, it took the form that is known as a 'turtle back' where the centre section is horizontal, but then the edges sloped down at an angle to where will meet the belt armour. This in turn meant a shell penetrating the main belt would then strike the inclined deck armour behind it at something 70 degrees, and be unable to penetrate it even if the shell had survived penetrating the belt armour intact. This page has some good depictions of the Bismarck armour belt and deck layout.

http://www.kbismarck.com/proteccioni.html

The following shows how Bismarck compares to King George V;

https://s-media-cache-ak0.pinimg.com/or ... 3596ad.jpg

As you can see, the armour deck in KGV is carried higher up and as a single thickness. This is important as a single thickness is much better than several thinner plates that add up to the same total thickness, because the thiner plates each lose up to 30% of their strength, meaning a 3" plate behind another 3" plate will have a relative resistance of about 4" or so (with some differences due to the armour manufacture etc), so inferior to a single 6" plate.

Now comes the actual answer to your question, as plunging fire as experienced at longer ranges stikes at very different angles, shells will be striking a horizontal surface at maybe 60 - 80 degrees down to 45 - 60 degrees depending on velocity and range. This makes it far easier to penetrate the deck as although the impact angle is less favourable, the armour itself is thinner. With Bismarck is it possible for a shell to pass over the main armour belt and strike the deck behind it, but more importantly a shell can penetrate the thinner upper belt area and then strike the inclined armour behind it, which will present the shell with an angle close to 90 degrees and thus give the shell the best possible chance to penetrate. At longer ranges, the deck area of a ship will represent something like 80% - 90% of the target area, so most incoming shells will strike there rather than the belt.

With the armour being so low down in the hull on Bismarck, many vital communication systems and crew passages were above the armour belt, and thus easily disabled by hits on the deck area, as even non-penetrating hits would explode on the armoured deck and devastate the areas and systems above it. At closer ranges this would be less important as the side of the ship would present maybe 60% - 80% of the target area, would make deck hits far less likely. In the final action, the control areas in the fore part of Bismarck such as the fire control and bridge. were out of contact with the stern facilities, meaning the guns were firing under local control only, and any orders given were heard in some parts of the ship and not others. With focused control for the guns lost, the ship becomes relatively harmless (if that is the right word for a 50,000 ton warship with huge guns onboard!), and even if the steering had not been disabled it may have proven impossible to transmit orders to the engine and steering control areas as communication systems were put out of action.

Of course, the benefit of having the deck so low is that it creates a very effective water-tight raft with the armoured citadel of the ship, meaning that it is very difficult to sink even if everything above above the raft is very quickly disabled. This area will slowly flood from progressive flooding and whatever direct damage it takes that allows water to pass through, so a ship Bismarcks size could be expected to float for quite a long time even if everything above this armoured raft is destroyed.

Just as an aside, with a ship the size of Bismarck it could be expected that if an attempt to scuttle it were made in a calm harbour setting, it would likely take between 90 - 120 minutes to actually sink (similar to the scuttled capital units at Scapa Flow in 1919) from that cause alone (Bill Jurens, the naval forensic expert, agreed with this assessment of mine several years ago, and he had direct acccess to the blueprints of the ship), so unless the crew had actually begun to scuttle Bismarck as soon as KGV and Rodney started to engage, scuttling cannot have been the cause of her sinking. It would contribute to the speed she sank certainly, but the major factor in the sinking would always be the damage she had sustained. Hope this helps.

User avatar
Pips
Member
Posts: 1226
Joined: 26 Jun 2005 08:44
Location: Canberra, ACT, Australia

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by Pips » 15 Jun 2017 00:16

Thanks Terry, your explanation clear's a lot of things in my mind. Goes a long way to explaining why the upper decks of the Bismarck became a slaughterhouse with resulting loss of control and command, yet the hull remained (comparatively) intact.

That link for the Bismarck v KGV is interesting. If I'm reading it right, it shows that the KGV was better armoured (as in thicker) over it's key area's than the Bismarck. Is that right?

How does the KGV, and Rodney, compare in the upper deck protection to the Bismarck? Same? Better?

User avatar
Terry Duncan
Forum Staff
Posts: 6059
Joined: 13 Jun 2008 22:54
Location: Kent

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by Terry Duncan » 15 Jun 2017 23:50

I was planning to add another post as I forgot to mention a few details in my reply, but it is covered in your question about Bismarck vs KGV so I will answer it in this post.
Pips wrote:Thanks Terry, your explanation clear's a lot of things in my mind. Goes a long way to explaining why the upper decks of the Bismarck became a slaughterhouse with resulting loss of control and command, yet the hull remained (comparatively) intact.
The superstructure, everything above where the side of the ship ends, is almost entirely only plated to keep out lighter shells at long and medium ranges, not to stop heavy shells as that would mean too much weight high up in the ship. At close ranges most shells from anything larger than a destroyer, have a good chance of penetrating anything but the heaviest armour, so adding more and more weight is pointless. The thin armour ships did carry above the deck area would typically not be thick enough to detonate a heavy shell, or slow it down enough for it to explode inside the ship, the theory being it would pass out the other side and explode there. With Bismarck the armour on the side was good against short to medium ranged shells, but allowed anything passing over the belt to explode inside the ship, above the armoured citadel, but amongst the crew areas and crew passages throughout the ship, which in turn would make evacuating harder as areas became impassable, and see any crew in this area very vulnerable anyhow.
Pips wrote:That link for the Bismarck v KGV is interesting. If I'm reading it right, it shows that the KGV was better armoured (as in thicker) over it's key area's than the Bismarck. Is that right?
This is the part I sort of forgot a detail about previously. Shells have a fuse that is set to explode the burster inside the ship fractions of a second after the armour sets it off. This is why the US tried to have the 'decapping' armour before the main armour, the intention being to either distort the nose cone of the shell and render the shell dud, or to set the fuse timer running so the shell would explode harmlessly on the main armour as it would not have time to penetrate now. We are talking hundreths of a second, but in that time the shell can travel dozens of feet, or pass through several inches of armour if it is still intact. With the KGV the armour is designed to all be in the area the shell strikes first, putting all the defence on the front line effectively, so shells without enough mass and velocity would explode on the very thick armour this approach allowed, but also ensuring the armour slowed any shell passing through it enough that it would explode just inside the armour where the standard 10mm plating or so of a deck or two would see the fragments kept out of the vitals even if they did then wreck the crew areas above them. With Bismarck the ship is relying on several layers of less thick armour to slow or detonate the shell, but as the thinner plates offer less effective resistance than one single thick plate, there is a lot of weight wasted. The main risk is that a shell penetrating the main armour would not be slowed enough, or rendered dud after doing so, and still have enough energy and mass to allow it to penetrate the plate behind the main armour, then explode. For KGV you would have three decks below the main armoured deck before you reached the vitals, meaning a shell was unlikely to get beyond the armoured deck and first internal deck before exploding, and the fragments would then penetrate only one or two more decks at a much reduced velocity. On Bismarck this would mean any shell penetrating the main armour and the medium plate behind it would be exploding directly in the vitals themselves or only one deck above them. If the main armour fails, serious damage is far more likely.
Pips wrote:How does the KGV, and Rodney, compare in the upper deck protection to the Bismarck? Same? Better?
KGV is far superior in armour layout, that is where the weight saved by using 14" guns went. The main deck is comparable with any other ship bar Yamato, give or take fractions of inches. Rodney is a curious case as she was a great design cut down all round to meet a strange treaty imposed limit, and then accidently coming out 1,500 tons below the limit meaning more could have been done without cutting so much weight. The belt armour is internal and inclined, like on some US ships, which is great at resisting damage, but a real pain to repair as you need to remove the side of the ship to access the belt armour! On Rodney is also is very shallow, meaning a lucky shell could strike underneath the belt entirely and enter the vitals, effectively the 'freak' hit scored in Japanese tests that led to them trying to build a shell that would dive through the water and strike under the belt if it fell just short of the target. Rodney is also unusual as all the best armour is clustered around the main armament, allowing the thickest armour to be over a very short length of the hull. The machinery is protected well, by a secondary thickness in all cases, meaning that the ship is easier to disable regarding maneuverability than it is to disable the main armament of detonate a magazine. Given the limits of the treaty it was a very good design, the best of the pre-1935 ships, and other than the Nagato whos speed was unknown, the fastest battleship in the world when entering service. The 'she was very slow' is totally hindsight from a WWII perspective, though if the desired design had been built it would have ben capable of 31-32kts. Bismarck would have done well to avoid Rodney if given the chance, her armour really cannot cope with the 16" shells. Against KGV it is far closer, but mostly in that whilst Bismarck is unlikely to hurt KGV unless she closes to close range, by entering a range where her own guns can penetrate with certainty, she has also entered the range where KGV's shells are also capable of penetrating her own armour. After that it is down to pure luck really.

All of this makes it look like Bismarck was a really bad design (she sort of was) but that is not entirely the case. She was a good ship, could outrun any ship she couldnt stand a good chance of beating (only the three British battlecruisers had much chance of catching her when she was designed), had a good main battery, good secondary and tertiary batteries too, enough armour to keep out shells from almost any ship than came close to her speed, and keep out shells from every ship that could catch her. She is a very large ship, hard to sink, a good gun platform, and equipped with very good fire control for the time. Where she fails, and fails really badly, is in that she is well over 42,000 tons, and on the full load displacement over 50,000 tons (full load is useful as 'standard tonnage' differed from nation to nation as they all sought ways to snip a few hundred or thousand tons off the 'standard' figure, but full load is often closer to the operational weight to be expected), and only really comparable to ships 10,000 tons lighter than her. There is so much wasted weight in the design because of inexperience in the design field post-WWI, so an interesting comparison is with the British G3 or even H3a/b/c designs from 1921, which are of similar weight.

PS. You may also like to see my recent posts in the pinned 'Z Plan' thread as they deal with a Tirpitz vs Massachussetts scenario, but with a bit more discussion on the armament area.

User avatar
Pips
Member
Posts: 1226
Joined: 26 Jun 2005 08:44
Location: Canberra, ACT, Australia

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by Pips » 16 Jun 2017 00:18

Again thank you. I will browse the Z Plan thread.

I am surprised by the comments on the armour layout of the Bismarck. I was under the impression that the Germans were more knowledgeable at designing armour layout than the British a 'la High Seas Fleet battleships and battlecruisers.

Thoddy
Member
Posts: 154
Joined: 18 Jun 2017 11:37
Location: Germany

horizontal protection of Bismarck-class

Post by Thoddy » 18 Jun 2017 18:32

This is important as a single thickness is much better than several thinner plates that add up to the same total thickness, because the thiner plates each lose up to 30% of their strength, meaning a 3" plate behind another 3" plate will have a relative resistance of about 4" or so (with some differences due to the armour manufacture etc), so inferior to a single 6" plate.
Anyone who is concerned with the armor protection of Bismarck-class battleships, should deal with "Spaced Arrays" i.e. complex targets. This "magic word" is true for the side protection of Bismarck class as well as the horizontal protection.

"Lump sum claims", that single plate of given thickness are always better then proper designed spaced arrays do not apply to this special case.

The horizontal protection (wheather deck 50 mm and main armor deck 80 mm) offer protection in the order of 150 mm (6 inches) versus artillery type attack. Magazine protection is increased accordingly. (50 mm + 100 mm -> ~170-180mm).

excerpt from Unterlagen zur Bestimmung der Hauptkampfentfernung und Geschosswahl(Translation)
...Regarding the safety of horizontal protection against penetration, it should be noted that results at relatively small impact angles can only be an indication for expected penetration. Small material variations frequently have a great impact, so for example, differences in the cap shape (cap removal) and hardness (of the plate) can affect penetration abilities in such a way, that in one case, the projectile enters the plate and in the other case, under otherwise the same conditions, ie at the same impact velocity, but with different cap, the projectile will be rejected. Also, the values, both of the angle as well as the impact speed at which a projectile is dismissed or just penetrates the plate, often influenced each other so closely, that they can not be separated exactly. A further contributing factor is, that in cases of relatively low impact angles, the elusive nature of straightening up of the projectile has even more influence, than at larger impact angles. This effect can be found especially when several plates have to be penetrated. It is even also possible that the projectile enters the plate with an angle to the direction of flight, so it has to penetrate with a much larger cross section.
This was approved by british ballistic research wich evaluated the protective value of the horizontal protection scheme beeing 6 inches (status as per 12/1945 past shootings against the german horizontal scheme) i.e. no british gun available at this time could pentrate trough this horizontal protection at ranges at least below 30 kyard. The findings were written into a series of ballistics reports dating from 1945 - 1950
SUPP 22-68 SPACED ARMOUR.jpg
High obliquity attack of deck targets.jpg
Bismarck evaluation.jpg
This is why the US tried to have the 'decapping' armour before the main armour, the intention being to either distort the nose cone of the shell and render the shell dud, or to set the fuse timer running so the shell would explode harmlessly on the main armour as it would not have time to penetrate now.
no american battleships posses a decapping system, wich reliable decaps incoming ordnance. Neither intentionally ("US tried to have ") nor coincidentally as the hull plating was to thin for decapping.
at least for german projectiles
decapping.JPG
where the standard 10mm plating or so of a deck or two would see the fragments kept out of the vitals
even splinters from relatively small calibers can pentrate 10 mm of steel easily
Splitterwirkung.png
hope this helps
You do not have the required permissions to view the files attached to this post.
Last edited by Thoddy on 19 Jun 2017 12:23, edited 1 time in total.
"Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!"

Thoddy
Member
Posts: 154
Joined: 18 Jun 2017 11:37
Location: Germany

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by Thoddy » 19 Jun 2017 12:00

They also thought the most likely engagement she would fight would be at close or medium ranges under North Sea conditions, for which she is a very good design indeed.
No these ships(Panzerschiffe F+G= Bismarck+Tirpitz) were intended to counter french battleships following the Dunkerque class actively in the Atlantic (as per 1936/37). A potential deployment of these ships in confined waters was expected to be too restricted by shortranged enemy ships and later aircraft especially torpedo carrying units.

The german K-Amt dealt with 2-4 gun turrets since WWI. Since that time military requirements and legal conditions has been weighted at several occasions. The three gun turret of the Panzerschiffe was a design compromise dictated by the available weight.

Only the 2 gun turret on a four turrets ship fullfills a extensive catalogue of military requirements. Main requirements for main artillery were:
the ability to engage two main targets with heavy artillery at the same time,
simplicity in operation,
susceptibiliy (against internal and external interference) under combat conditions,
shooting sequence,
costs.
There is so much wasted weight in the design because of inexperience in the design field post-WWI
the Germans "wasted" much weight in redundancy and range.
for instance
- fuel oil ~7,700 m³
-16,000 t/hour drainage capacity
-100 percent redundancy in firecontrol
-100 percent redundancy in powerplant performance.
- extensive compartmentalisation

But it's another question if this helps against repeated battle damage 2,000 miles from the next own naval base.
and even non-critical hits against unarmored parts of a ship can slow it down.
"Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!"

Tsofian
Member
Posts: 49
Joined: 05 Apr 2017 14:49
Location: St Louis, Missouri

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by Tsofian » 13 Jul 2017 00:12

The Bismark design was a rework of the World War One Bayern class. Those vessels mounted 4 twin 38 cm guns. It was far easier for the Germans to update the design and keep the twin turrets than to start from scratch.

CharlesRollinsWare
Member
Posts: 184
Joined: 23 Apr 2005 21:15
Location: Windsor Locks CT

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by CharlesRollinsWare » 02 Aug 2017 00:22

Gents;

You cannot properly compare any prewar USN BB design to the choices other nations might make because regardless of what might be best, the American ship would be built with a key fixed dimension - beam - as said ship HAD to be able to pass through the Panama Canal. No European nation necessarily had such a consideration :)

That said, all nations ships were restricted to the maximum size of the extant slipways and dry docking facilities unless they intended on building a new facility - like the French chose to do for SS Normandie - and possibly draft - which was a consideration for construction facilities in shallow water dockyards/harbors.

Thus, proper analysis of design choices must recognize such considerations!

Mark E. Horan

User avatar
T. A. Gardner
Member
Posts: 2906
Joined: 02 Feb 2006 00:23
Location: Arizona

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by T. A. Gardner » 07 Aug 2017 05:30

CharlesRollinsWare wrote:Gents;

You cannot properly compare any prewar USN BB design to the choices other nations might make because regardless of what might be best, the American ship would be built with a key fixed dimension - beam - as said ship HAD to be able to pass through the Panama Canal. No European nation necessarily had such a consideration :)

That said, all nations ships were restricted to the maximum size of the extant slipways and dry docking facilities unless they intended on building a new facility - like the French chose to do for SS Normandie - and possibly draft - which was a consideration for construction facilities in shallow water dockyards/harbors.

Thus, proper analysis of design choices must recognize such considerations!

Mark E. Horan
The British were confined on size by the size of their existing dry docks. These were built, at the latest, in the 19th Century and put a big constraint on beam in particular. That's why the KGV has such a narrow one compared to other contemporary battleships.

The US in the pre-war years built a series (always dry dock #4 for some reason) at Naval shipyards on both coasts. These new dry docks were over 1000 feet long and 200 feet wide. They are designed to take any foreseeable ship that might be built in the future and are large enough to handle a US aircraft carrier today.

Germany's restriction was draft. The Kiel Canal was wide but not particularly deep so their ships tended to have more beam and less draft as moving through this canal was a requirement for them.

Thoddy
Member
Posts: 154
Joined: 18 Jun 2017 11:37
Location: Germany

Re: Why did the Germany navy stick to dual-turrets for the Bismarck-class?

Post by Thoddy » 07 Aug 2017 13:02

The Bismark design was a rework of the World War One Bayern class.
According to own statments of the german naval command the Bismarck was not a rework of the Baden design.
The Bismarck design line follows the path of the "Große Kreuzer" conception, wich also includes the Panzerschiff design as predecessor design.

We may speak about an evolutionary design compromise evolved from newly formulated main requirements regarding range (Atlantic-capable), protection(against 38 cm shells even at long range) and firepower(combat two battleship-targets simultaneously with main artillery) and Speed + secondary conditions (such as draft); especially the expected french answer to Littorio.

The finally choosen design "best fits" these requirements in a given system of contractual arrangements. And finally even this design compromise exceeds contractual size restrictions.
"Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!"

Return to “Kriegsmarine surface ships and Kriegsmarine in general”