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BaryOnyxx

Correction from Nathan Okun

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Hello Friends,

 

   Mr Okun contacted me with a correction to his calculations:

 

To all,

 

As you see below, Mr. XXXXXX showed that I made an error in determining the obliquity angles on the sloped deck; they should be 55.1 degrees at 10,000 yards and 52.88 degrees at 15,000 yards.  Corrections are made in the text below.

 

Nathan

 

 

 

Nathan,

 

In my opinion, the angle of impact (from the normal) on the sloped deck 60 degs. from vertical should be...

 

     at 10,000 yards:  60 - 4.9 = 55.1º

     at 15,000 yards:  60 - 7.12 = 52.88º 

 

... deducting the angle of exit from the vertical belt from 60º instead of adding it. Do you mind to revise your calculations, pls.?

 

 


From: Nathan Okun 
Sent: 29 October 2017 23:31
To:XXXXXXXXXXXXXXXXXXXXX
Subject: Armor penetration of BISMARCK Belt+Sloped Deck+Torpedo Bulkhead Adjacent to Forward Superfiring Turret by Italian 15" APC Shell

 

Dear Mr. XXXXXXXX

 

Looking at your BISMARCK diagram, the 110mm (4.33") sloped Wh-armor (= US WWII STS in quality) deck is at 60 degrees sloped inboard from the vertical at this narrowed ship width abreast Turret BRUNO -- usually 68 degrees amidships where the ship was wider -- and the 320mm (12.6") KC n/A belt+50mm (1.96") cement+~20mm (0.787") Schiffbaustahl III hull (= ~16.5mm (0.65") Wh-armor) waterline belt (KC n/A is slightly inferior in quality to US early-WWII Thick Chill Class "A" armor -- my Standard Armor -- but it has a thinner face layer for reduced scaling effects, which more than compensates against large-caliber shells, like the 15" shell we are considering here) is sloped outboard at 10 degrees (close enough).  The Italian 381mm (15") M1934 APC projectile weighed (average) 885 kg (1951 lb, slightly more than the British WWII 15" Mk 17B -- Italian APC shells were originally based on British pre-WWI APC ammo and kept the general design concept of the heavy shell, though fired at a significantly higher MV than the British did these heavy shells).  I cannot find detailed data on the projectile AP cap and windscreen weights, so I am going to assume the AP cap weighs 12% of the projectile total weight (234 lb or 106.2 kg) and the windscreen weighs 3% (58.5 lb or 26.5 kg), making the bare-nosed body weight 752.3 kg (1658.5 lb).    The MV was reduced from the original value of 870 m/s (2954 ft/s) to reduce excessive barrel wear problems to 850 m/s (2789 ft/s), which I assume is what you are using.

 

I will be using my latest penetration computer programs:  FACEHARD Version 7.8 FACEHD78 (face-hardened armor, here KC n/A plus hull backing layers) and HCWCALC Version 3 HCWCLCR3 (homogeneous armor, here Wh and Ww).

 

Using FACEHD78, at 10,000 yards the APC shell hits the belt just above the waterline at  ~701 m/s (2300 ft/s) at an angle of fall of ~4.9 degrees -- estimate from the range table value at 10,000 m (10, 936 yards) of 687 m/s (2284 ft/s) and an angle of fall of 5 degrees.  This gives an obliquity angle of 10+4.9 degrees = 14.9 degrees on the KC n/A+backing belt, with no horizontal component, assuming BISMARCK's Target Angle is ~87 degrees (moving slightly toward the Italian BB) to take the curvature of BISMARCK as it narrows toward the bow into account.  Running the shell data, armor data, striking velocity, and impact obliquity into FACEHARD ARMOR SELECTION #10 (Krupp KC n/A, which also includes its WWII special-purpose thin-plate KNC and Thin-Chill Armored Tube KC due to lack of any test data to the contrary) and ITALIAN PROJECTILE SELECTION #12 (assumes a direct upgrade of WWI-era post-Jutland British Mk 5A APC design, not the later deformable British APC actually used in WWII, which may be wrong, but no contrary data)., the NBL for complete penetration is 390.1 m/s (1280 ft/s), the shell's body (AP cap and windscreen are now gone) is now moving forward at 467.6 m/s (1534 ft/s) with no noticeable damage and no yaw or wobble (other than the usual tiny nutation -- ignored here -- due to the shell's spin through the air) and, since the obliquity was under 15 degrees, no deflection, either, so the projectile is still moving downward at ~4.9 degrees toward the sloped 110mm Wh deck plate.

 

At 15,000 yards the APC shell hits the belt just above the waterline at  ~625.7 m/s (2053 ft/s) at an angle of fall of ~8 degrees -- estimate from the range table value at 15,000 m (16, 404 yards) of 620 m/s (2034 ft/s) and an angle of fall of 8.7 degrees.  This gives an obliquity angle of 10+8 degrees = 18 degrees on the KC n/A+backing belt, with no horizontal component, as above.  Running the data, armor data, striking velocity, and impact obliquity into FACEHARD ARMOR SELECTION #10 again, and ITALIAN PROJECTILE SELECTION #12 again, the NBL for complete penetration is 390.1 m/s (1324 ft/s), the shell's body is now moving forward at 381 m/s (1250 ft/s) with no noticeable damage and no yaw or wobble and an upward deflection of 0.88 degrees, so the projectile is moving downward at ~7.12 degrees toward the sloped 110mm Wh deck plate.

 

Note that very large chunks of belt armor have been thrown out of the plate back as the face and anything behind it are cracked out and pushed through the plate ahead of the projectile and at an equal or even higher speed.  These will ricochet off of the 110mm sloped deck and tear up the unarmored internal hull above this deck, which is two decks high to the weather deck, since the magazine roof 90mm (3.54") Wh flat main armored deck, from which the sloped deck's top edge is attached, is only slightly above the waterline.  This loss of such a large volume of protected reserve buoyancy across the entire ship width and probably at least two average compartments or even more in length parallel to the ship centerline directly behind the hole in the belt means that just because a shell does not penetrate the sloped deck and is deflected upward by the sloped deck, the ship still pays a heavy penalty for a shell penetration of the belt or, even worse, for a plunging fire penetration of the thin upper belt or weather deck.

 

Now the bare-nosed, medium-length-blunt-point 1658.5-lb projectile body hits the 4.33" Wh sloped deck at 60 - 4.9 = 55.1 degrees (****CORRECTION!!!****) at 10,000 yards or at 60 - 7.12 = 52.88 degrees (****CORRECTION!!!****) at 15,000 yards, going 1534 ft/s or 1250 ft/s, respectively.  Switching to HCWCLCR3, we now input the respective values and we get:

 

                1)  ****MAJOR CORRECTION****:  The 10,000-yard NBL is 316.4 m/s (1038 ft/s), well below the striking velocity, and the Remaining Velocity is 349.6 m/s (1147 ft/s) -- most of the resistance is due to glancing effects, not actually slowing the projectile, so the velocity after penetration is much higher than against a solid vertical plate of the same NBL hit at right angles -- with a deflection of 6.7 deg downward, so the impact obliquity on a vertical plate would be 4.9 + 6.7 = 11.6 degrees, so a complete penetration occurred, and the remaining velocity is easily enough to penetrate the vertical, downward-dropping 50mm (1.96") Ww-steel (Krupp's US Navy WWII HTS replacement for such things; roughly 0.85 times its Wh equivalent quality = ~1.67" Wh) anti-torpedo "holding" bulkhead located at the joint of the sloped and flat decks.  However, the fuze delay of the projectile must be over about 0.029 second, on the average, to allow the entire average distance from the belt through the Ww plate going at the Remaining Velocities given above before the fuze causes the shell to detonate.  Since the British used, after Jutland, a 0.025-second delay (taken from the nominal delay used by the German Krupp poorly-designed delay-action fuzes they studied after that battle, and, to my knowledge, kept that delay from then on), it is possible that the Italians kept that delay too, though the German and US 0.035-second design time (0.033-second for the WWII US Mk 21 BDF when actually tested) might have been used (only the Japanese, due to their underwater-hit diving Type 88 and Type 91/1 APC projectiles developed starting in the late 1920s, used much longer delays than this -- 0.2-0.4 second in the battleship-sized shells -- to my knowledge).  If the 0.025-second delay was retained from late-WWI or just after WWI, depending on when the Italians added a fuze delay to their ammunition, the shell has slightly less than a 50/50 chance to make it through the Ww plate before detonating, which might throw some fragments through that plate, but unless the fuze is a dud or fails to properly detonate the shell, in which case large-sized chunks of shell would hit and probably penetrate that plate, the damage behind the Ww plate would be minimal (a British 14" APC shell actually properly detonated due to fuze action just as it hit this Ww plate in the battle where the HOOD was sunk and just caused some leaks with minimal damage behind that plate, due to the shell being reduced to small-to-medium-sized fragments).  If the delay was 0.035-second or thereabouts, then the chance of penetrating the Ww plate is almost certain since a very short delay due to fuze failure, approaching the British delay, is highly unlikely due to the typical spread of delay values of a properly-functioning base fuze (maybe 10% chance) Therefore, there is a somewhat-less-than-50/50 chance of the Italian 15" shell penetrating all three plates and/or detonating properly behind the final Ww plate if the delay is similar to the British base fuze; but a close-to-certain (90%) chance if the longer German/US WWII fuze delay was used in these shells.

 

 

 

 

I will cut to the chase; at 10,000 yards, the Bismarck would have all but certainly fallen to a magazine hit from the Littorio's guns.  Turtleback, main belt, and torpedo bulkhead would all have been defeated by the shell, and the resulting hit would have had s roughly 90% chance of setting off the magazines.  

 

 

2)  ****MAJOR CORRECTION****:  The 15,000-yard NBL is 291.1 m/s (955 ft/s), well below the striking velocity, and the Remaining Velocity is 248.1 m/s (814 ft/s) with a deflection of 9.5 deg downward, so the impact obliquity on a vertical plate would be 7.12 + 9.5 = 16.62 degrees, so a complete penetration occurred, and the remaining velocity is easily enough to penetrate the vertical 50mm (1.96") Ww-steel (= ~1.67" Wh) anti-torpedo "holding" bulkhead located at the joint of the sloped and flat decks.   However, the fuze delay of the projectile must be about 0.039 second at least, on the average, to allow the entire average distance from the belt through the Ww plate going at the Remaining Velocities given above before the fuze causes the shell to detonate.  If the British 0.025-second delay was used in these Italian shells, the shell has almost zero chance of getting through the vertical Ww plate before detonating, which, as mentioned above, might throw some fragments through that plate, but unless the fuze is a dud or fails to properly detonate the shell, in which case large-sized chunks of shell would hit and probably penetrate that plate, the damage behind the Ww plate would be minimal. If the delay was 0.035-second or thereabouts, then the chance of penetrating the Ww plate is maybe ~35-40% due to the typical spread of delays in these fuzes, if the fuze works properly, with about a 15% chance of fuze failure (low-order detonation or a dud allowing large chunks or even an intact projectile through the WW plate, so the total chance of passing through the plate is 35-40% to give a high-order detonation and an additional 15% chance of just sending an inert projectile or several large chunks thereof through the plate (with less chance of setting off ammunition in this latter case).  There is only a ~35-40% chance of a 0.035-second-delay base fuze getting through the side and causing potentially major damage to the ship due to a magazine fire, but this drops to essentially zero with a 0.025-second fuze delay (the Japanese 8" AP shell underwater hit on USS BOISE that detonated high-order inside a main magazine filled with brass cartridge cases -- no exposed powder bags -- shows how such a properly-fuzed hit could cause a major fire and severe damage to the ship).  There is some chance of inert fragment damage if the base fuze fails to function properly, but this has a much lower chance of causing a magazine explosion due to the large number of powder bags being in brass cartridges and no high-temperature gases being present.

 

As to the non-magazine spaces near Turret BRUNO, but under the flat 90mm Wh main armor deck, they are relatively safe at 15,000 yards through the belt armor with any regular delay, either British 0.025-second or US/German 0.035-second, against a shell whose base fuze functions correctly, but have some possibility, though small when the fuze fails to function properly, of the shell or large chunks of it, making it through all of the armor layers to reach those spaces, though as inert chunks only.  If the designed fuze delay is close to the 0.025-second British value, the chance of making it entirely through the armor is only of any real possibility with an inert projectile due to a failed fuze, so if the fuze works properly, the fuze will cause the shell to never reach the Ww plate except in small-to-medium pieces.  At 10,000 yards, the fuze delay effect is much less, with only the short British 0.025-second delay in a properly functioning fuze keeping the shell from reaching the magazine spaces; the 0.035-second fuze would almost always cause major fire/explosion effects in the magazine if it works as designed and will still always allow the shell to reach the magazine with inert chunks, if not.  Interesting that poor, unreliable fuzes give better results in the 0.025-second-delay case, though not a high chance of causing a magazine explosion, in this case, isn't it?

 

Nathan Okun

 

 

 

   I promise to leave this topic alone after this:  I used Nathan's formulae to model a progressive battle between the two ships, starting at 40,000 yards, and closing.   The Littorio won in 7 out of the 9 encounters I ran, which amazed me.   The key to the battle seemed to be the fact that the Littorio's guns were able to start doing serious damage to Bismarck's vitals long before the latter could do the same.  In a case like this one, success seemed to hinge on who could do real damage first, and that seemed to be Littorio.  

 

 

 

 

 

Peace.

 

Edited by Rotten_Fish
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5 minutes ago, renegadestatuz said:

Why are you so fixated on the Littorios being able to pen Bismarck? What’s the point?

Fan fiction? :cap_fainting:

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1 hour ago, renegadestatuz said:

Why are you so fixated on the Littorios being able to pen Bismarck? What’s the point?

Same as any other of the countless "this ship vs. that ship" discussions that are posted on these forums....

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1 hour ago, TTK_Aegis said:

Fan fiction? :cap_fainting:

That too!    :fish_book:

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@Rotten_Fish, please censor out Mr. Okun's email address. To my understanding, he would not want his email address to be publicly available like this, as it would open it to numerous spambots.

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14 hours ago, DeliciousFart said:

@Rotten_Fish, please censor out Mr. Okun's email address. To my understanding, he would not want his email address to be publicly available like this, as it would open it to numerous spambots.

Good call.  Thanks for the heads up.

 

Peace

 

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