Bismarck vs. Iowa

[Constance]

Thanks guys, I've read the thread, and it wasn't too clear for me.

People will always have biased opinions, and I didn't like what the guy said to me. I want to hear peoples opinions on the matter, do you think Bismarck was a terrible and mediocre battlewagon? Or something different? I know what you've all said in this thread, but I want to hear it straight and clear, if that's too much trouble, you don't have to say anything...

[lwd]

One of the serious problems in comparing Bismarck to either Yamato or Iowa is the latter two were designed to fight at long range in compliance with the doctrine of their respective navies. The Bismarck designed more for the closer ranged battles of the North Sea. The Germans were also well pleased with the survivability of their WWI capital units which managed to make it back to port with considerable damage. If you look through the various threads on this forum you will see that the "All or Nothing" design theory predominated in most navies between the wars this was not true of the Germans. Some use this as a point against Bismarck. On this forum some have presented a fairly strong case from it being a different rather than an older and inferior design philosophy.

[Karl Heidenreich]

Bismarck was suited to fight at long range as with those other two vessels. But I concurr in general terms with the armor scheme statement lwd made. Different concepts with strong and weak points as with everything technical in this world. The AoN also presents several tendencies, as with the sloped external belt armor of North Carolina and intended for USS Montana vs the internal one of South Dakota and Iowa. Still it seems that the "stronger" approach for the AoN was made in Yamato.

[Thorsten Wahl]

from
http://warships1discussionboards.yuku.c ... protection
quote from my own

Excerpt from "Unterlagen zur Bestimmung der Hauptkampfentfernung..."

Based on the experience of Worldwar I and as a result of the development of weapons, armor protection has been improved primarily in the following aspects:

against hits that can occur on large distances and correspondingly large angles of incidence against the armordeck
against bomb attacks

These two reasons force you to use a significantly larger portion of the armor weight on the horizontal protection and barbettes, but the total proportion of armor to the total weight can not be increased substantially. The barbettes must, if they are not covered by closed casemates, etc., go through at full strength about the main armored deck, as in the case of larger angles of fall of these parts are not completely covered by the side armor. By this new distribution of the armor, it is not possible to make the belt armor so strong, that it cannot be penetrated by “heil” projectiles.

It must therefore be sought, to integrate also the horizontal armor in the system of vertical protection. If this can be achieved, it is possible, at least on the main combat distances to keep the destructive impact away of vital parts of the ship.

The strongest armored deck therefore has to be lay as deep as possible with a flat slope as possible to the lower edge of the main belt, but, unlike previously, now so strong that even projectiles, wich penetrates the belt with a significant surplus of speed and hit the slope, can not penetrate, but get breaked or dismissed.

On the other side the armored deck itself cannot be made as strong to prevent any penetration of projectiles that hit the armored deck directly at the highest distances, because such a substantial reinforcement of the armoured deck, that it also protects against the heaviest AP- shells at larger angles of incidence seems impossible for large parts of the vessel from weight issues . By increasing thickness of armor plate its only possible, to push out the distance at which penetration occurs.

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.

As these (combined) effects couldnt be explained in every detail they are not considered in the recommendations for optimal combat-distances against enemies.
Insofar the recommendations has to be counted as worst case scenario.

Allied ballistic research during and past ww2 seems to confirm the german approach.
british research for instance consider for horizontal protection a value of 6 inches for a battleshiptarget similar to Tirpitz (SUPP 6/481 Proc q 4,016) against 16 inch projectiles in 01/1946. So "vital parts" of the german ships seem to be save against british projectile at distances up to 30 kyard against horizontal penetration compared with an estimate of ~22 ky according C.B 04039 Armour Protection(1939) addendum no.2 1943.

US research on smaller calibers shows under certain circumstances a potential better protection for spaced plates vs single plates by a net factor of up to 1.3 - 1.5.
http://www.dtic.mil/srch/...ction=t3&id=ADA954865

Regardless from the gain in protection for vital parts, the german approach requires large parts of the ships to be destroyed or crippled. In this context, the assessment of the german authorities is worth mentioning, that turret protection of Bismarck-class was found to be inadequate for the combat-value of the SK 38 weapon.

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in the last time i could aquire some additional informations on the british tests against spaced deck targets
the tests against Bis target scheme were probably conducted around 07/45 according
A.R.D. Terminal Ballistics Report No. 7/45(This is a old reference number not used now). This report i couldnt aquire until now but there were strong notes on this in

DEFE 15/490 High obliqity Attack on deck targets Part III
"Earlier experiments, in wich 20 mm calibre scaled down models of 15" A.P.C. shell were fired against targets scaled down to represent composite battleship decks, are described in (A.R.D. Terminal Ballistics Report No. 7/45) High Obliquity Attack of deck targets."

After this experiment the british seem to consider Bis/Tir deck protection as being equivalent to 6 inch single plate as described in SUPP 6/481 Proc q 4,016.

[RobertsonN]

Do you know if the 6 in applies to the 50 + 80 mm combination over the machinery or the 50 + 100 mm over the magazines?

A further point about the HKE (written in 1940) for Bismarck (against Royal Sovereign, Nelson and Dunkerque) is that they all give the panzer deck over the magazines as 110 mm both on the flat and slopes, rather than the 100 mm flat/120 mm (slopes) combination usually given. This has the effect of increasing the difference of the upper edge of the immunity zone between machinery and magazines, e.g., against Royal Sovereign it was IIRC 19300 m for machinery and 25000 m for magazines.

Another point about Suppl. 6/481 is that it is more pessimistic about deck penetration at long range than the RN was earlier in the War: it was now thought that the new British 16 in gun could penetrate 6 in of deck armor only at 34000 yds for the shell best suited to deck penetration.

[alecsandros]

against Royal Sovereign it was IIRC 19300 m for machinery and 25000 m for magazines.

An essential element which is to often disregarded is armor quality. The Royal Sovereign was a WW1 build, with WW1 armor quality. IIRC the pre-1920 British armor was about 10-15% less resistant to battleship caliber shells than the British post-1930 CA.

[RobertsonN]

The figures of 19300 and 25000 m apply to the Bismarck when hit by British shells from a 15/42 gun. The shells were assumed to be of modern shape and materials (i.e. not of WW1 era).

[alecsandros]

The figures of 19300 and 25000 m apply to the Bismarck when hit by British shells from a 15/42 gun. The shells were assumed to be of modern shape and materials (i.e. not of WW1 era).

Excuse me, I misunderstood.

[Karl Heidenreich]

Thorsten,

Thanks for the very valuable quote.

Regards,

[Thorsten Wahl]

but even the scheme offers protection for the parts below the Panzerdeck in remote attacks, Bismarck type ships must take into account probably more successive damage to the parts above the panzerdeck compared to the other ship, when their shells didnt pentrate trough the armor deck and belt.
on the other side most other ships has less protected shiplenght so hits in these areas are able to make also a difference or hits affecting areas outside of the belt increasing drag and lowering speed

They should be well advised to make a decision - slip into a distance range where they can pentrate through their enemys belt or leave the battlefield. my personal opinion.

[RobertsonN]

In general, this is true, however the Bismarck did have more equipment below the middle deck than any other ship, because its citadel was so much longer (550 ft). Only the Hood was similar. In BS the following were below the middle deck:
(1) All munitions;
(2) Main machinery;
(3) All electric generating plant and the auxiliary boiler;
(4) C3 elements: command centre, all fire contol computers, 4 damage control rooms, radio room, battle radio room, decoding room (radio room B), some electric cables and communications (details unknown to me);
(5) Some of the electric, gunnery and machinery spares;
(6) Most of the provisions.

In addition, the rest of the provisions and some more spares were underneath the armored deck aft.

In Italian ships all, and in American ships some, of the diesel generators were outside the citadel; in the Richelieu the auxiliary boiler was above the MAD.

It's a question really of what the volume given maximum protection was. In Bismarck this volume was shallower but longer than in any contemporary.

In comparison to Baden the volume taken up by items (3) and (4) was much more; and was the main reason why the German ships grew in size between the First and Second Wars.
Item (2) was also larger. The ships of WW1 had cramped machinery spaces because they were intended to operate in the North Sea in the main. The Bismarck had the larger machinery spaces Raeder wanted for oceanic raiding.

[RobertsonN]

I'd like to pose a question.

What was the inner edge of the Iowa's IZ against the Bismarck?

The Iowa's belt was the equivalent of 17.3 in vertical at 25 deg angle of fall (figures for the US 16/45 2240 lb).

From Gkdos 100 curves for the German 15 in, 17.3 in of vertical armor could be penetrated at 18000 m where the angle of fall was 13.9 deg. So there would seem to be penetration here. I lack the means to work out the approximate value of the inner edge though. The problem would seem to consist of two parts: (1) How did the effective vertical thickness of the Iowa's sloped belt vary with angle of incidence? (2) How much was allowed for resistance due to structure?

Answers appreciated.

[alecsandros]

I'd like to pose a question.

What was the inner edge of the Iowa's IZ against the Bismarck?

The Iowa's belt was the equivalent of 17.3 in vertical at 25 deg angle of fall (figures for the US 16/45 2240 lb).

From Gkdos 100 curves for the German 15 in, 17.3 in of vertical armor could be penetrated at 18000 m where the angle of fall was 13.9 deg. So there would seem to be penetration here. I lack the means to work out the approximate value of the inner edge though. The problem would seem to consist of two parts: (1) How did the effective vertical thickness of the Iowa's sloped belt vary with angle of incidence? (2) How much was allowed for resistance due to structure?

Answers appreciated.

The 17.3" is overly optimistic, to say the least. IT was calculated with the capabilities of pre-war 2240lbs APC shells in mind, which had rather poor oblique penetration capabilities.
The thickest portion of the armor was 12.2" (310mm) class A, inclined at a certain angle. The class A armor had rather poor performance against BB sized shells, with estimates ranging from 10-25% less resistance to penetration than British plates of the same thickness.
German armor plates that were tested in Britain yielded about the same test results as the British plates had.

German 38cm gun/shell were tested against Krupp KC n/A FHA armor, and that's how GkDos curves were obtained.

The German 35/38cm L4.4 APC shells were tested to obliquities of up to 60* from the vertical (30* from the horizontal) and managed good perforations.

Tests performed by Krupp with the L52 38cm gun showed perforations of 308mm KC n/A at 25km, with the plate inclined at 20*.

Given the above-mentioned problem with Class A armor, I guess the 38cm L4.4 shell could perforate the main belt at ranges in excess of 25km.

So to answer your first question, the Iowa belt angle improved protection only in relation to certain types of projectiles. The amount of improved protection was very small against German 38cm L4.4 and US 2700 Mk43, for example, because those shells were particularly designed to function well during oblique penetration processes.
========

N.B.: the real obliquities, in real naval battles, were bigger, as they were compounds of tri-axial obliquities. The above scenario only concerns the vertical obliquity, the one most usualy taken into account when discussing imunity zones.

[RobertsonN]

Thanks for, what is to me, is a surprising reply. I believed the US APC shells with their blunt 0.5 crh heads were better at oblique impact than the German 1.3 crh shells. I appreciate though that the effective vertical thickness of a sloped belt is reduced a little against shells with a flatter trajectory like the German 15 in. What was a disadvantage in deck penetration was an advantage in belt penetration.

[alecsandros]

A few details, curtousy of David Saxton:

38cm L52 gun Krupp tests:

A 38cm L/4.4 fired from the 38cm/L52 gun, against KC plates also declined by 20* obtained the following results:

20km-364mm
21.8km-350mm
25km-308mm

"The basic design of the L/4.4 projectile dated to 1935.[ii] During this time frame the German Military, and such firms as Krupp, instituted a new three-tiered testing regime. Projectiles were tested, or proofed, by striking plates at 30*, then 45*, and then 60*.[iii] The L/4.4 design tested extremely well up to the most oblique striking angles.[iv] In a 1945 report American metallurgy experts determined this performance was due partly to the unique approach of welding the high alloy tip of 0.93 caliber radius onto the main body of the projectile.[v]
The Americans determined that when striking armor, a typical armor piercing shell’s hard cap will first stress the plate before it is destroyed. In the German design, the shell’s welded-on-tip then digs further into the armor before it is in turn destroyed. The welded-on-tip of the spinning projectile will spall off and form a more or less flat section across the weld seam during oblique impact, rather than spalling off conically as is the usual case. The main body of the shell then acts as a flat nosed punch while driving through the remaining armor. If the tip spalled off conically, a projectile would be more likely to glance off or “scoop” during oblique impact, rather than drive though the remaining armor.[vi] "