Naval History Forums

Hello,
Does anyone know for what conditions was Bismarck's IZ calculated ? I.e. target angle, and artillery caliber.

I'm asking because, at right angles, everything above the main armor belt was vulnerable to 38cm gunfire out to 23-24km or more.

I would think Bismarck IZ was calculated versus her own 15 inch guns.
The IZ considers immunity of the ships vitals not everything above the main armor belt.

OKM documents signed by Kurt Assman (OKM documentarian) state the (vitals) IZ of Bismarck must be from 20km to 30km vs the German 38cm gun. Bericht 166... also speaks to the trade offs and the IZ calculations of the new battleship designs. Of special concern is the extraordinary belt penetration of the 38cm compared to existing 15", and 16", and still providing sufficient belt protection, when so much armour weight must now be expended for deck protection compared to older battleship designs.

Dave Saxton wrote:OKM documents signed by Kurt Assman (OKM documentarian) s

Excuse me, but was his name realy Assman ?

alecsandros wrote:

Dave Saxton wrote:OKM documents signed by Kurt Assman (OKM documentarian) s

Excuse me, but was his name realy Assman ?

Wow, now we see who's REALLY "hilarious". All over the board, from advocate to authoritarian to puerile...looks like #8 member on my ignore list, effective in less than 10 seconds from this post.

Bismarcks IZ against ist own guns was considered with
inner IZ 20 km
outer IZ 30 km

Quot from an own actual post on the "NavWeaps Discussion Board"
http://warships1discussionboards.yuku.c ... 673/type/0

Outer IZ
according Unterlagen zur Bestimmung der Hauptkampfentfernung und Geschoßwahl Heft h Schlachschiffe Bismarck und Tirpitz
Impact condition
velocity: ~460 m/s
AOF : ~32°

horizontal penetration nominally versus homogenous armor: ~130 mm
50 + 80 mm =130 mm (Simple addition of protective plating without further explanation)

Inner IZ 20 km ther is also some similar crude over the thumb estimate.

Impact condition
velocity: ~510 m/s
AOF : ~16°

vertical FH armor nominal penetration ~420 mm
320 mm + 100 mm =420mm (another simple addition with some rounding)

For outsiders these informations appear plausible on the first view as they correspond with actual plate thicknesses, but without further explanations these protective values are completely misleading as they omitted key facts. These figures were first used in the admirality "Wargame 1938/39".

key facts arise from the terms: "spaced armor" for deck protection and the "Böschungsdreieck"(wich is also some kind of spaced armor with non parallel plates)

Thanks Thorsten,

Any idea how they judged the internal armor array ? For example, the 220mm barbette (the part beneath the weather deck) - what kind of armor was that ? Wh, KC ? How did they expect to behave when hit by 380mm APC shell ?

Did they expect full decaping by the 50mm Wh weather deck / 145mm KC upper belt (depending on trajectory), and thus considered 220mm of rounded armor sufficient to stop a decapped 380mm shell ?

alecsandros wrote:, and thus considered 220mm of rounded armor sufficient to stop a decapped 380mm shell ?

Not stop but destroy. A de-capped heavy caliber AP would be destroyed upon impact with 220mm of KC. The 14" hit on South Dakota's Class A barbet is a good example.

According to Schmokle & Koop the only place I can see barbette @ 220mm was the rear of the turret barbette on the Tirpitz. The rest is 340mm.

mind you looking at this site a layered 145mm + 30mm + 220mm curved.
http://www.kbismarck.com/proteccioni.html

Should average out to ~20" resistance against 15''-16" shells.

Barbetteprotection citadel area
-upper belt 145mm
-Barbette armor below whetherdeck down to the armored deck 220mm

according ADM 213/951 German steel armour piercing projectiles and theory

about 1/2 Caliber thick FH armour should shatter any incoming decapped projectile in service at the time
at impact angles against the barbatte armor near normal (0°-10° obliquity) penetration by fragments appears possible but no detonation inside

so this combination is sufficent up to about 440 mm AP projectiles of typical german Quality.

within the barbette ther is also an additional bulkhead (20 mm made from ST52)

Thanks guys.

Any thoughts on to how the GErmans treated barbettes/turrets that were hit ? I.e. ok, let's say the 220mm barbette will stop the decapped shell - but would it still be left in fighting condition ?
Same case for turrets - the 360mm thick KC faceplate would stop many attacks, but the attacks themeselves would probably incapacitate the turret as a fighting force.

Did they use some sort of shock absorbers or other method for dispersing shock damage ?

hits against turrets and barbettes likely cause shock damage and requires immediate and accurate evaluation. When doubts arose, about the further viability, the equipment concerned, was not used until dockyard inspection.

As happend with South Dakota. They didnt use the turret, wich was hit but not penetratet for precautionary reasons. Wich is comprehensible. Much the same as the german standard procedure of immediate flooding magazines, when hits occur in the vicinity of magazines. Preventing catastrophic detonations was the primary purpose. Pumping and re-commissioning of equipment should be a minor problem.

Nevertheless the damage to the 1,5" wheter decks speaks more for a HE hit as the HE content of an armor piecing shell likely cannot create a hole of the documented size.

alecsandros wrote:Thanks guys.

Any thoughts on to how the GErmans treated barbettes/turrets that were hit ? I.e. ok, let's say the 220mm barbette will stop the decapped shell - but would it still be left in fighting condition ?
Same case for turrets - the 360mm thick KC faceplate would stop many attacks, but the attacks themeselves would probably incapacitate the turret as a fighting force.

Did they use some sort of shock absorbers or other method for dispersing shock damage ?

I suspect that a shell that penetrates the 50mm deck could then strike the 220mm barbette with sufficient striking velocity to penetrate it as well, even if the shell is decapped.

The 360mm faceplate angled back at only 15degs, if the turret is aimed at the firing ship would present a very low obliquity target and would be penetrated by most Allied battleship guns at all but the longest ranges.

dunmunro wrote:
I suspect that a shell that penetrates the 50mm deck could then strike the 220mm barbette with sufficient striking velocity to penetrate it as well, even if the shell is decapped.

There was also the possibility of a shell striking the weather deck in a position close to the barbette (say 1 meter distant from the barbette), and not becoming fully decapped until the moment when it came in contact with the lower (220mm) barbette.

This is one of the reasons I thik the 80mm armor extensions around the main turrets could have served as true armor, instead of "only" structural purpose.

BUT as clear schematics of this white elephant (the 80mm armor on the weather deck around the main barbettes) are nowhere to be found (at least by me), and only fragmentary evidence exists here and there, I can only speculate.

the thick part of Bismarcks barbettes did not end at the whether deck. It reaches until about 50 cm below that deck.
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"There is a possibility of the wheter deck being 80 mm thick around the main artillery."

But this seems very uncertain. Possibly Herr Nilsson knows more.
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"The 360mm faceplate angled back at only 15degs, if the turret is aimed at the firing ship would present a very low obliquity target and would be penetrated by most Allied battleship guns at all but the longest ranges."

For such hits Bismarck had the least eggs in the basket to say.
To aim for the faceplate, your ship must be resonable close to the target- at a distance no armor offers protection anymore, with the likely exception of that "german Böschungsdreieck".
As the range increases the faceted german turrets presents a resonable small target compared to the total area, we can expect from impact spread. Nevertheless even non pentrating hits may put a massively protected turret out of action as happend with South Dakota"(already mentioned above. This hit requires a check at the dockyard according to the damage report.

Additionally even the 40 degrees leaned back faceplates of US BBs offer a relatively "low obliquity" target.
at 22,5 km (~25kyard) range, AOF of the german projectile is about 20 degrees impact speed here about 480 m/s
At "Grenzschußcondition" this projectile is expected to pentrate about 410 mm armor with KC na Quality.
But german armor plate in this thickness was found to be of superior quality compared to US plates requiring about 7-8% more Limitvelocity for successful penetration of US AP-projectiles. And the type of armor used in US faceplates unlikely break up the german projectile.
Here we have a borderline problem. I cannot derive for certain if protection is given or not for several faceplates used in allied ships.