Nagato protection

[dunmunro]

the upper deck on american Battleships was made of STS

Comparison D-Steel vs St-52

comment imperial-Elongation and DIN-Dehnung (delta5) are not comparable as the german specification uses a relatively longer specimen
D Steel an armour grade material??? wishful thinking IMHO

There were different grades of D steel and welding grade was judged less efficient as light armour and for holding bulkheads.

This is a false dichotomy. Stating that any material must meet some minimum standard otherwise it disappears or becomes transparent is ludicrous. If the KM used a particular steel for a particular purpose (such as light armour) then we examine it's effectiveness for that purpose and we wouldn't assume that it disappears if it doesn't fit into an arbitrary category.

[hans zurbriggen]

Hello,
to Mr. Dunmunro writing: " .0805 calibre plate thickness begin to be effective for decapping at high obliquity"
Another interesting aspect on which we can agree to disagree: it surely depends on obliquity, but other sources speak of up to almost 0.2 calibers to get de-capping at 90° impact angle, and only when using armor-grade materials. I agree we cannot dismiss the thin layers in a precise calculation, but even in the scheme you posted this KGV weather layer is not considered at all. Comparing different battleships, we cannot count for them.

and to Mr. Wahl writing: "D Steel an armour grade material??? wishful thinking IMHO"
I fully agree.

hans

edit: of course 0.2 calibers and not 2 calibers as I had previously written. Sorry.

[Thorsten Wahl]

As i said in my earlier reply imperial Elongation is different from DIN-Dehnung (5)

Using the same specimen as imperial measurings the 18% "Mindest" Dehnung(5) translates into about 24% Elongation or "as you dont want"
33% according to the comparison sample.

Okun states that .0805 calibre plate thickness begin to be effective for decapping at high obliquity.

this is a value obtained from a US report on decapping on scirting plates of german Panzers.

Decapping Tests(Kappenabschlagstests) were common in testing of german armor piercing ammunition. In Britain such "Standard Tests" were introduced after WW2.

For ensuring decapping of major naval projectiles german recommendations were at least 0,2 cal plates in flight direction /100 mm for a 38 cm Psgr respective 60 mm for a 20,3cm Psgr.
Head shape of the projectilebody had considerable impact on the attachment of the cap. Hemispherical shapes appeared as inferior in this regard.

[dunmunro]

Hello,
to Mr. Dunmunro writing: " .0805 calibre plate thickness begin to be effective for decapping at high obliquity"
Another interesting aspect on which we can agree to disagree: it surely depends on obliquity, but other sources speak of up to almost 0.2 calibers to get de-capping at 90° impact angle, and only when using armor-grade materials. I agree we cannot dismiss the thin layers in a precise calculation, but even in the scheme you posted this KGV weather layer is not considered at all. Comparing different battleships, we cannot count for them.

and to Mr. Wahl writing: "D Steel an armour grade material??? wishful thinking IMHO"
I fully agree.

hans

edit: of course 0.2 calibers and not 2 calibers as I had previously written. Sorry.

Shell fire will never strike at 90deg obliquity, and bombs rarely do. 31mm of D steel will certainly initiate fuze action on AP bombs, will slow the bombs velocity and help ensure that, even if it penetrates the MAD, it will detonate well short of the magazine.

You have a table of various steels presented to you, showing 'D' steel having all the desired qualities to act as light armour (and is directly compared to 'average nickel steel armour') and yet you refuse to acknowledge that.

[hans zurbriggen]

Hello Mr.Dunmunro,
I am afraid I have given you the values of tensile strength demonstrating that D steel cannot be considered even close to an armor grade steel, the same concept Mr.Wahl explained to you.
ST52 steel (the one used for mere hull plating of Bismarck) had hardness of 150 Brinell and tensile strength of 64kg/mm2.
Your own posted table shows hardness 160 Brinell for the best D-steels (vs 150 for ST52) and tensile strength of 78 (vs 74 for ST52) but you don't specify the measurment units used in the posted table, I guess the difference with my figures is in measurement units (metrics vs anglosaxon)
Please look at the values I have given you for the true armor grade steels above (e.g. the ones Germans used in WWII, all Krupp /nA (neuer Art = new type, much better than WWI ones).
Please, admit D steel could have been (possibly) considered armor grade in WWI, against soft cap WWI shells. By WWII, it was not much superior than a construction steel like ST52.

Also, according to the article of Mr.Okun you yourself have posted (http://www.navweaps.com/index_tech/tech-085.php), a German WWII hard cap (Type II) shell cannot be de-capped with less than 0.12 caliber plates (around 45 mm for a 380 mm shell at 20° descent angle, in the table it is 70° obliquity, or 49 mm for 406 mm shell) and only hard cap Type I shells can be decapped with 0.0805 caliber (31 mm steel for 380 mm shells, 33 for 406 mm).
Therefore KGV weather deck was a splinter deck, not a de-capping deck. It could have slowed (very, very marginally) incoming large caliber shells, but it could defeat neither them nor their cap. Check yourself the values in the below table, please, if you trust Mr.Okun.

hans

tech-085_Decap_pic_reduced.jpg (85.99 KiB) Viewed 4203 times

[dunmunro]

Hello Mr.Dunmunro,
I am afraid I have given you the values of tensile strength demonstrating that D steel cannot be considered even close to an armor grade steel, the same concept Mr.Wahl explained to you.
ST52 steel (the one used for mere hull plating of Bismarck) had hardness of 150 Brinell and tensile strength of 64kg/mm2.
Your own posted table shows hardness 160 Brinell for the best D-steels (vs 150 for ST52) and tensile strength of 78 (vs 74 for ST52) but you don't specify the measurment units used in the posted table, I guess the difference with my figures is in measurement units (metrics vs anglosaxon)
Please look at the values I have given you for the true armor grade steels above (e.g. the ones Germans used in WWII, all Krupp /nA (neuer Art = new type, much better than WWI ones).
Please, admit D steel could have been (possibly) considered armor grade in WWI, against soft cap WWI shells. By WWII, it was not much superior than a construction steel like ST52.

Also, according to the article of Mr.Okun you yourself have posted (http://www.navweaps.com/index_tech/tech-085.php), a German WWII hard cap (Type II) shell cannot be de-capped with less than 0.12 caliber plates (around 45 mm for a 380 mm shell at 20° descent angle, in the table it is 70° obliquity, or 49 mm for 406 mm shell) and only hard cap Type I shells can be decapped with 0.0805 caliber (31 mm steel for 380 mm shells, 33 for 406 mm).
Therefore KGV weather deck was a splinter deck, not a de-capping deck. It could have slowed (very, very marginally) incoming large caliber shells, but it could defeat neither them nor their cap. Check yourself the values in the below table, please, if you trust Mr.Okun.

hans

d.jpg

Actually it states a Brinell value of 170 for 'D' steel.

Again, what other nations used for deck plating doesn't make KGV's decks suddenly vanish. The fact is that the RN used D steel as light armour and the Soviets used it for tank armour, so it must have had some value as armour plate...and in fact, compares very well with the average nickel-steel armour given in the same table.

You again use this strange form of binary thinking, when you conclude that KGV's weather deck might not decap a KM38cm AP round so therefore it is of no use in decapping, but then state that it actually can decap other designs up to 15in (38cm) calibre, as though KGV's only designed or potential opponent must be Bismarck.

In any event Bismarck's guns have very flat trajectory and so a KGV magazine penetration was unlikely under 32k yds (according to the KM) and even at maximum range stood little chance of penetrating KGV's MAD and subsequently reaching KGV's magazines. Strangely, despite her weather deck's supposed decapping ability, the KM concluded that the RN 15in could penetrate it over the machinery from about 21k yds and over the magazines from about 27k yds.

According to the Naval Armour and Ballistics calculator (NAaB 2.1), KGV's weather deck is sufficient to reduce SV by ~75fps at ~32k yds, which significantly degrades the KM 38cm AP shells ability to penetrate the MAD, even though the shell is not decapped (except for the BC).

[hans zurbriggen]

Hello Mr. Dunmunro,
you write: "it states a Brinell value of 170 for 'D' steel.": only for post WWII D steel, not KGV one.
and: "...compares very well with the average nickel-steel armour given in the same table": table refers to 1890-1925 steels (WWI), not the nichel-chrome-molibdenum WWII (e.g. the German Krupp /nA ones).
and "...as though KGV's only designed or potential opponent must be Bismarck": KGV weather deck can de-cap neither 406 mm Type I American shell (requiring 33 mm) nor Japanese 410 - 460 mm, in addition to Type II German 380 mm. Who were KGVs designed to fight against ? French and Italian only ? (and still debatable, as ~31 mm are needed for de-capping a "normal" Type I 381 shell). All thicknesses are according to Mr.Okun above graph.
and: "...KGV's weather deck is sufficient to reduce SV by ~75fps at ~32k yds": hardly a significant reduction out of striking velocity of ~1500fps, against a counter-productive slight deflection toward normal to MAD of a still capped shell.

I repeat: we both agree that KGV horizontal protection was one of best among all BB's, possibly best one over mags (due to their strong MAD/splinter layer and mags position down into hull), but please let's try to stay to facts and not to overstate them. The weather deck on KGV was against splinters and small caliber shells, not considered by most texts (as your mentioned "Allied BB's") as a protective layer integrating the MAD.

hans

[Thorsten Wahl]

Strangely, despite her weather deck's supposed decapping ability, the KM concluded that the RN 15in could penetrate it over the machinery from about 21k yds and over the magazines from about 27k yds.

Against ships with the british 15" gun the KM considered a battledistance of 12 - 18 km as optimal for decisive action, despite the calculated "fact" that also the horizontal protection was no longer safe at this distance.

The calculations for optimal battledistances were always made - considering a projectile with optimal performance (no yaw no projectile degeneration) against all layers of armor. The additional protective effects were mentioned "only superfically" for the knowledgeable reader in the textbook.

A significant part of the not or only superficially mentioned protectives effects, arises only when taking into account the whole knowledge gathered about armour penetration of complex targets.

complex targets may have or may not have an additional protective effect. And thes effects may differ with the type of projectile, size or shape or other unknown/uncertain factors.

The british learned -after the war- that certain arrangement may increase proection against certain typ of attack. and realised that the german horizontal protection had an protective equivalaent of About 6 Inches of single plate.

-uncapped attack of standard 15" projectiles against 200 lb/sqinch plates at 60 degrees angle of incidence increased the ballistic Limit for complete penetration by about 18 percent compared to the same projectile with cap.
At higher angles of incidence the additional effect is mor prounounced

The same general result can be found in american ballistic research about spaced armor. A proper arrangement of two plates may allow for weight savings of about 10 to 20 per Cent for the same protective effect as one single plate considering Yaw and decapping.

[dunmunro]

Hello Mr. Dunmunro,
you write: "it states a Brinell value of 170 for 'D' steel.": only for post WWII D steel, not KGV one.
and: "...compares very well with the average nickel-steel armour given in the same table": table refers to 1890-1925 steel, not the nichel-chrome-molibdenum WWII (e.g. the Krupp /nA ones, see data provided).
and "...as though KGV's only designed or potential opponent must be Bismarck": KGV weather deck can de-cap neither 406 mm Type I American shell (requiring 33 mm) nor Japanese 410 - 460 mm, in addition to Type II German 380 mm. Who were KGVs designed to fight against ? French and Italian only ? (and still debatable, as ~31 mm are needed for de-capping a "normal" Type I 381 shell). All thicknesses are according to Mr.Okun above graph.
and: "...KGV's weather deck is sufficient to reduce SV by ~75fps at ~32k yds": hardly a significant reduction out of striking velocity of ~1500fps, against a counter-productive slight deflection toward normal to MAD of still capped shell.

I repeat: we agree that KGV horizontal protection was one of best among all BB's, possibly best one over mags (due to their strong MAD/splinter layer and mags position down into hull), but please let's try to stay to facts and not to overstate them. The weather deck on KGV was against splinters and small caliber shells, not considered by most texts (as your mentioned "Allied BB's") as a true protective layer.

hans

The table states post WW1 for D steel.

Again, so even though D steel compares well with a nickel-steel armour it suddenly vanishes because it might not be as effective as a type of armour used on Bismarck. Rather than analyzing the KGV deck protection scheme as the sum of it's whole, you prefer to simply make parts of it vanish.

It doesn't matter what shells the weatherdeck can or cannot decap, it still exists as a significant part of ship's horizontal protection and like the KM the RN probably didn't consider decapping as a factor in deciding what the immune zone was for the MAD and/or the magazines.

75fps is a very significant reduction when the SV is already less than 1500fps and it pushes the probable deck penetration outward considerably, by about 4k yds. This is a key consideration against high MV guns as their shells will always strike the weatherdeck with high obliquity.

I didn't mean to derail this thread, but only to point out what seemed to be a minor error on your part, but your stubbornness in refusing to acknowledge the totality of KGV's deck protection, is dragging this out. This is from an RN study comparing KGV and Tirpitz's magazine protection:

[Thorsten Wahl]

This is from an RN study comparing KGV and Tirpitz's magazine protection:

to be exact it#s from C.B. 04039 (2) (20 th July 1942) Addendum No 2 to C.B. 04039 ARMOUR Protection, 1939.

For both armor schemes the britsh recommendations left out the upper deck as having any protective effect.
In the german case they definatily made a mistake when leaving out the upper deck.

In the other case its uncertain, If ther were positive or negative effects.

-Does the upper deck decaps.
-Is the one deck distance between upperdeck amd main deck sufficent to develop yaw above the so called optimum yaw , wich may increase vunerability of multiple plate arrangements.(comment the rate of development of yaw is increased if the shell was decapped)

yaw - deviation of the angle of the projectile axis from the flight path

Ther is a available american report on ballistic tests against a models of american deck schemes, wich indicates a somewhat reduced effectivenes compared to single plate.

[dunmunro]

This is from an RN study comparing KGV and Tirpitz's magazine protection:

to be exact it#s from C.B. 04039 (2) (20 th July 1942) Addendum No 2 to C.B. 04039 ARMOUR Protection, 1939.

For both armor schemes the britsh recommendations left out the upper deck as having any protective effect.
In the german case they definatily made a mistake when leaving out the upper deck.

In the other case its uncertain, If ther were positive or negative effects.

-Does the upper deck decaps.
-Is the one deck distance between upperdeck amd main deck sufficent to develop yaw above the so called optimum yaw , wich may increase vunerability of multiple plate arrangements.(comment the rate of development of yaw is increased if the shell was decapped)

yaw - deviation of the angle of the projectile axis from the flight path

Ther is a available american report on ballistic tests against a models of american deck schemes, wich indicates a somewhat reduced effectivenes compared to single plate.

The KGV weatherdeck is certainly going to initiate fuze action and it will decelerate bombs and shells. Again, whether this results in decapping and/or yaw is debatable but we cannot pretend that the deck doesn't exist. Similarly the existence of two 12.5mm 'D' steel decks and the 38mm splinter deck over the magazines becomes a vital factor if the MAD is penetrated and the shell/bomb detonates short of the magazine (as it most probably will).

Like all designs we have to examine the entire protective scheme, especially as we accumulate more knowledge of AP shell and AP bomb penetration.

[Thorsten Wahl]

Like all designs we have to examine the entire protective scheme, especially as we accumulate more knowledge of AP shell and AP bomb penetration.

Agree.

[hans zurbriggen]

Hello,
to Mr.Dunmunro writing: "...your stubbornness in refusing to acknowledge the totality of KGV's deck..."
I am extremely disappointed to see these kind of personal comments, especially as I would have so much to say regarding the same attitude from your side.

I have no problem admitting my mistake regarding the D-steel post WWI data, but I see you don't acknowledge your mistakes re. mixing nichel steels of WWI era with WWII armor grade steels, re. KGV deck being sufficient for de-capping (when it was not, per your own sources) and re. D-steel being an armor grade one (Brinell hardness of pure construction steel ST52=150, D-steel =170, armor grade (e.g.Wh /nA)=250, everyone can make up his mind based on what you yourself posted as reference).

Therefore, despite we all (since the beginning) agree about 'we have to examine the entire protective scheme', I will discontinue this by now unproductive discussion with you re.KGV, hoping you will do the same, to avoid very unpleasant drifts, being back to Nagato protection.

hans

[Dave Saxton]

I have primary documentation of the WW2 D steel mechanical properties.

D above 20 lbs thickness: Tensile: 74,000 psi, Yield: 66,000 psi, Elongation: in 8" 17% C content: 0.26%-0.36%
DW: Tensile: 70,000 pSI, Yield: 42,000 psi, Elongation in 8": 17%, C content: 0.23%

[Dave Saxton]

I also have primary documentation on ST52:

Tensile 53.3kg/mm^
Yield 37kg/mm^
Elongation: 32.4% (in what length is not given)