Plunging fire

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delcyros
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Re: Plunging fire

Post by delcyros »

Bgile,
don´t misunderstand me, I´m not revisioning the ricochet strories. Just wondering whether the reference for idea that the main belt of BISMARCK was almost submerged was based on anecdotical evidence or the damage controll flooding report of BSIMARCK which is said to exist and was rescued by one of the survivors. I haven´t seen this document, ever.
But what I´have seen is the belt arrangemet of BSIMARCK. It had a comparably high armoured freeboard (for the standarts of the period) with only VANGUARD having an even higher armoured freeboard in service condition. At construction displacement, this belt extended almost 10ft amidships (3.0m) and 12ft at the extreme turrets (+3.6m) above the design waterline, this may have been lower in service conditions at deep load but not by as much as it was for TIRPITZ, displacing a lot more with all the additions TIRPITZ received in the first place:

Image


I don´t know how much fuel, provision, drinking water and ammo was spend by the time of her final battle but he should have been 5,000 metric tons lighter than before leaving Norway (not topped off with max. fuel), hadn´t she been damaged and torpedoed in the meantime. Neither can I assess the flood damage before the final battle but as I mentioned before, in order to levelise the waterline at the level of the upper/main belt joint, another 15,000 tons of flooding are required in addition to the 5,000ts of water I assume to remain in the ship as a cause of the damage and counterfloodings (a wild guess, I admit).
At TIRPITZ deep combat load, the chances are roughly 60/40 for upper belt / main belt hits (50/50 at the turrets) with regards to area´s exposed. It´s still far from the belt going to be submerged or difficult to hit. But then again, by the time, RODNEY was closing in for the kill, a lot has happened and the exact timetable doesn´t exclude that by then BISMARCK´s sea valves already opened and thus the ship starts to sink slowly taking over water.
Billy
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Re: Plunging fire

Post by Billy »

The German cap was a fair bit heavier than its British counterparts. I would find it very unlikely that they would have used old ww1 armor in tests since the newer armor had been around for some time by them. However could it be that the German figures were correct (especially regarding German tradition regarding fastidiousness and accurate records)regarding their figures of their armor penetration. Could it not be that the German shells due to their different design actually exceeded the penetration values of other navies. Given the similarities between German and British armor and the exhaustive tests that the shells were put through, and the thorough record keeping of each navy, and the differences in German shell design,can it not be said that German shells were superior by a large margin.
Swiftman
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Re: Plunging fire

Post by Swiftman »

26-inch thick armor from Japanese Yamato class battleship, pierced by a US Navy 16-inch gun. The armor is on display at the US Navy Museum

https://scontent-ord1-1.xx.fbcdn.net/hp ... e=574EE2EC
Siegfried
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Re: Plunging fire

Post by Siegfried »

dunmunro wrote:By "belt" I presume you are both talking about the 320mm portion of Bismarck's main belt:
Image
The majority of the belt was located above the waterline (3.0/1.8 meters as designed, but 2.6/2.2 meters in practice), with the reasoning that shells are more likely to hit above than below the waterline.
Bismarck's draft increased by 1.3 meters at 53000 tonnes (extreme deep) from 45.5k tonnes (design). Given the underwater damage and counterflooding required to correct lists prior to the last battle, it seems reasonable that Bismarck was probably displacing somewhere between 52-55k tonnes at the start of the battle and somewhat more than this by the time Rodney closed the range. At 53k tonnes, only 1.7m of the main belt would be exposed above the waterline, and at 57k tonnes only about 1 metre of the main belt would be exposed, and this only represents a small fraction of average target height. At very close range, shells are unlikely to plunge when striking the water and given the gale force weather, shells with a trajectory that would carry them into the main belt are very likely to strike a wave prior to hitting the belt.
Do we know whether the Bismarck's lower deck "Tortoise Shell" armour was ever penetrated?
Thorsten Wahl
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Re: Plunging fire

Post by Thorsten Wahl »

In the context of the evaluation of the horizontal protection "Battleship H", fears were expressed, that the horizontal protection consisting of a 50 mm upper deck and 100 mm armored deck could already penetrated at angles of fall of 15 ° - 25 ° (corresponding to a distance of at least around 20 km).

The Navy Weapons Office(Marinewaffenamt) therefore carried out fullsize ballistic tests with 40.6 cm armor piercing shells, which were able to dispel the fears.

It is confirmed that there is a risk to the horizontal protection with regard to penetration through the armored deck (penetration whole) requires a angle of fall of about 27 ° corresponding to a distance of 30 km.
Hauptgefährdung Panzerdeck Schlachschiff H.jpg
Hauptgefährdung Panzerdeck Schlachschiff H.jpg (85.21 KiB) Viewed 5669 times
(Bundesarchiv BA-MA RM 20/1913 Akte Oberkommando Kriegsmarine AV Allgemeine Typfragen für Schlachtschiffe, Panzerschiffe und Kreuzer (02/1939- 12/1939) Schreiben Marinewaffenamt M WA Ia 759/39 g-Kdos. vom 6. April 1939)

The document took me 10 years of search and about 10000 pages of documents.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!
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hans zurbriggen
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Re: Plunging fire

Post by hans zurbriggen »

Hello Mr. Wahl,
thanks for sharing this extremely interesting document. Was test done using the 1,030 kg APC shell of German 40,6 cm (SK C/34) ?
May I ask you if you could find any test done against the combination of main belt + slope instead of upper deck (or upper belt) + main deck ? Which was the range (if any) under which the belt/slope combination could be defeated according to these tests ?

hans
Thorsten Wahl
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Re: Plunging fire

Post by Thorsten Wahl »

The test was obviously done with 40,6 cm /1030 kg APC (Psgr) as the AOf data is only conform with the 40,6 cm projectile
(the 38 cm projectiles reach 27 degrees AOF at about 27 km)
Which was the range (if any) under which the belt/slope combination could be defeated according to these tests ?
test are unknown up to now, but in "Unterlagen und Richtlinien zur Bestimmung der Hauptkampfentfernung..." they used a additional textual explanation using the wording:
" Es muss deswegen angestrebt werden, soweit irgendwie möglich, auch den Horizontalpanzer in das Gesamtsystem des Seitenschutzes einzugliedern. Hierdurch kann erreicht werden, dass wenigstens auf den Hauptgefechtsentfernungen die Zerstörungswirkung von den lebenswichtigen Teilen des Schiffes ferngehalten wird. "

It must therefore be seek for, as far as possible, to integrate the horizontal armor into the overall system of side protection. In this way it can be achieved that at least at the main combat distances [/ b] [/ u] the destructive effect is kept away from the vital parts of the ship.

As main combat distances they give 12-18 km against various battleships these distances correspond with distances at wich own guns may perforate enemies side protection.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!
Thorsten Wahl
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Re: Plunging fire

Post by Thorsten Wahl »

With regard to the splitted arrangement.

Not every splitted arrangement of deck protection may reach the same or better results of ballistic protection as a single plate of same total thickness.

British ballistic research gave requirements for the positive case
1) detachment of armor piercing cap (ADM 281-37 The ballistic performance of Non-Cemented, Cemented and Face Hardened Deck Armour (200+240 lbssqft) under attack by decapped APC)
at 60 degrees angle of incidence, the speed required for perforation of single armor plate for usual decapped armor piercing projectiles was increased by about 15 - 20 % percent compared to the same capped armor piercing projectile

2) sufficent distance between first deck and armor deck to develop sufficent yaw., (DEFE 15-490 High Obliquity Attack of Deck Targets. Part III, it was a series of three reports describing high angle attack of deck targets.)

Yaw is a double edged sword. It may assist or prevent perforation, depending on development of yaw.
-The yaw increases steadily after perforating the first plate.
-Decapped projectiles develop yaw faster.

With so called "Optimum Yaw" a shell may perforate a plate of given thickness far below its expected ballistic limit ( 20-40%).
The "Optimum Yaw" region lies for Armour piercing projectiles in the region of about 15 degrees projectile tilt towards armor plate compared to the line of flight.
But if yaw was sufficent, the projectiles usually failed to perforate by topple. It makes a somersault on impact of the main armour plate.
Image

The german armour scheme is probably the only one possessing a first deck with sufficent thickness for potentially decapping incoming projectiles and it was also the only one wich includes a distance of two decks until the main armour deck.

Further explanation see also SUPP 6-910 THE PENETRATION OF ARMOUR PLATE Summarized report of all british ballistic research up to 1951
Chapter four "Complex Targets.

British post WW2 research uprated Tirpitz horizontal protection to an equivalent of 6" single plate against british projectiles compared to earlier assessments.
In SUPP 6-481 Underwater performance of shells they described the target
"a target similar to the Tirpitz with dimensions as follow
-Beam 125 feet deck armour 6 inches
-vertical side armour 12 inches extending to 8 feet above waterline
-vertical underwater target equivalent to 2 inches extending from 8 feet below WL to 22 feet below WL.
.....
Chance of an effective hit .. against deck armour
...range 30000 yard; Nil..."

This report was written after the first "High obliquity attack of deck targets report" from July 1945
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Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!
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