Bismarck immunity zone

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alecsandros
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Re: Bismarck immunity zone

Post by alecsandros » Thu Jan 05, 2017 5:35 pm

.. During Bismarck final battle, there are 2 accounts mentioning direct hits on the turrets (aside from the early one that we do not know how happened). First account mentions Rodney's 406mm shells blowing the turret alltogether from point-blank range, the second mentions KGV's 356mm shell ricocheting from one of the turret faces (obliquity unknown, probably very unfortunate for the shell), range around 11.000meters. However the turret's guns are reported as losing hydraulic power and depressing at minimum elevation.

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Dave Saxton
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Re: Bismarck immunity zone

Post by Dave Saxton » Thu Jan 05, 2017 8:33 pm

Bismarck's face plates we not flat. The secant angles also must taken into account. I first learned about the secant from a 1920s USN text book.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

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Re: Bismarck immunity zone

Post by dunmunro » Thu Jan 05, 2017 11:41 pm

Dave Saxton wrote:Bismarck's face plates we not flat. The secant angles also must taken into account. I first learned about the secant from a 1920s USN text book.
The centre plate on the 38cm turrets looks flat to me:

http://www.kbismarck.com/photo018.html

and the only obvious variation is at the very far edges of the face plate where it fairs into the side plates.

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Re: Bismarck immunity zone

Post by dunmunro » Fri Jan 06, 2017 12:29 am

alecsandros wrote:.. During Bismarck final battle, there are 2 accounts mentioning direct hits on the turrets (aside from the early one that we do not know how happened). First account mentions Rodney's 406mm shells blowing the turret alltogether from point-blank range, the second mentions KGV's 356mm shell ricocheting from one of the turret faces (obliquity unknown, probably very unfortunate for the shell), range around 11.000meters. However the turret's guns are reported as losing hydraulic power and depressing at minimum elevation.
Post war testing showed that the RN Hadfield 14in could perforate (intact penetration) Tirpitz 320mm armour @ 30degs at 1370fps (versus 1460fps for RN 300mm armour @ 30degs). RN 15in Mk 17B could perforate 360mm of Tirpitz armour @ 30degs at 1640fps and the RN 14in generally had equivalent ability to the 15in on ~300mm plates while the 14in could perforate RN 350mm C armour @ 30degs at ~1800fps versus about ~1600fps for the 15in Mk 17B. Penetration (holing the armour) limits were ~100fps less.

Proof testing of the Hadfield 14in showed no tendency towards shatter at high SVs.

These test results indicate that the 14in and 16in shells had roughly equal probability of penetrating Bismarck's armour at the ranges and obliquities involved. It seems that assignment of most of the penetrating hits to the RN 16in gun probably just reflects bias on the part of the writers.

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Re: Bismarck immunity zone

Post by alecsandros » Fri Jan 06, 2017 6:46 am

dunmunro wrote:
These test results indicate that the 14in and 16in shells had roughly equal probability of penetrating Bismarck's armour at the ranges and obliquities involved. It seems that assignment of most of the penetrating hits to the RN 16in gun probably just reflects bias on the part of the writers.
Rodney was also closer to Bismarck , IIRC. So more impact velocity for her shells.

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Re: Bismarck immunity zone

Post by Herr Nilsson » Fri Jan 06, 2017 11:43 am

Thorsten Wahl wrote:
"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.
80 mm was just used around the middle and rear secondary artillery turrets.
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Re: Bismarck immunity zone

Post by alecsandros » Fri Jan 06, 2017 1:32 pm

Herr Nilsson wrote:
Thorsten Wahl wrote:
"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.
80 mm was just used around the middle and rear secondary artillery turrets.
Was it the same layout for Tirpitz ?

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Re: Bismarck immunity zone

Post by Byron Angel » Fri Jan 06, 2017 2:16 pm

Keep in mind that the citadel vertical protection scheme of the BISMARCK Class also incorporated a substantial internal glacis behind the belt (110mm Wh @ 22deg from horizontal, according to N Okun) to protect the vitals from low angle fire. Nathan's opinion is that no contemporary AP projectile was likely to pass intact through both belt and glacis.

FWIW.

B

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Re: Bismarck immunity zone

Post by Herr Nilsson » Fri Jan 06, 2017 7:13 pm

alecsandros wrote: Was it the same layout for Tirpitz ?
Yes
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Marc

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Re: Bismarck immunity zone

Post by Paul L » Fri Jan 06, 2017 8:31 pm

Byron Angel wrote:Keep in mind that the citadel vertical protection scheme of the BISMARCK Class also incorporated a substantial internal glacis behind the belt (110mm Wh @ 22deg from horizontal, according to N Okun) to protect the vitals from low angle fire. Nathan's opinion is that no contemporary AP projectile was likely to pass intact through both belt and glacis.

FWIW.

B

more importantly post war research started to show that complex targets of spaced plate tend to be 'greater than the sum of there parts'. It wasn't until computer driven photography+ laser measurement of the late 60s , that more refinement was possible. Issues like de-capping fell by the wayside and the damaging effects of yawed impacts on follow on plates and lateral strength of the penetrator became paramount.
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Re: Bismarck immunity zone

Post by Dave Saxton » Fri Jan 06, 2017 8:36 pm

dunmunro wrote:
Dave Saxton wrote:Bismarck's face plates we not flat. The secant angles also must taken into account. I first learned about the secant from a 1920s USN text book.
The centre plate on the 38cm turrets looks flat to me:

http://www.kbismarck.com/photo018.html

and the only obvious variation is at the very far edges of the face plate where it fairs into the side plates.
I have measured on the official drawings. It's not flat.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

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Re: Bismarck immunity zone

Post by dunmunro » Fri Jan 06, 2017 9:11 pm

Dave Saxton wrote:
dunmunro wrote:
Dave Saxton wrote:Bismarck's face plates we not flat. The secant angles also must taken into account. I first learned about the secant from a 1920s USN text book.
The centre plate on the 38cm turrets looks flat to me:

http://www.kbismarck.com/photo018.html

and the only obvious variation is at the very far edges of the face plate where it fairs into the side plates.
I have measured on the official drawings. It's not flat.
Here's a nice photo of a Tirpitz 38cm turret:

Image

it looks flat to me and any deviation from flat is very minor. Even the far edges are flat, unlike some drawings I've seen.

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Re: Bismarck immunity zone

Post by dunmunro » Fri Jan 06, 2017 9:16 pm

Byron Angel wrote:Keep in mind that the citadel vertical protection scheme of the BISMARCK Class also incorporated a substantial internal glacis behind the belt (110mm Wh @ 22deg from horizontal, according to N Okun) to protect the vitals from low angle fire. Nathan's opinion is that no contemporary AP projectile was likely to pass intact through both belt and glacis.

FWIW.

B
Of course, but all the externally visible armour on Bismarck was just about as likely to have been penetrated by the RN 14in as the 16in. Some accounts have all the penetrating hits ascribed to the 16in and all the non penetrating hits ascribed to the 14in - this just an indication of bias on the part of the writer and/or observers.

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Re: Bismarck immunity zone

Post by Herr Nilsson » Fri Jan 06, 2017 9:22 pm

Image
Regards

Marc

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Re: Bismarck immunity zone

Post by dunmunro » Fri Jan 06, 2017 10:33 pm

Herr Nilsson wrote:
thanks.

However. the mild curve (= ~8degs of rotation as seen from the firing ship) on the plate will have almost no effect on total obliquity if the turret is struck by a shell from targeted ship.

Also careful measurement of high res images of the turrets show the inclination to be less than 15degs (actually ~12degs).

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