The so-called "GKdos100"

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José M. Rico
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The so-called "GKdos100"

Post by José M. Rico »

Greetings to all after a few weeks absent,

I have started to upload to the website the English translation of the "Unterlagen und Richtlinien zur Bestimmung der Hauptkampfentfernung und der Geschosswahl", commonly known as the "GKdos100". This document was translated from the German by Ulrich H. Rudofsky many years ago, but I never put it online. So, I've been revising the whole text during the last couple of days, and I'm now uploading it to the site.
Booklet a), the text volume, has already been transcribed in HTML format and is accessible from the following link:

https://www.kbismarck.com/gkdos100a.html

Note: The original document is in the public domain, although I understand the copy we work with (that has been circulating all over the internet for the past many years) comes from Bill Jurens.

If you have any questions, comments, etc., this thread is open for discussion.
Bill Jurens
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Re: The so-called "GKdos100"

Post by Bill Jurens »

Very nice work. Thank you Jose.

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pgollin
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Re: The so-called "GKdos100"

Post by pgollin »

.

Thank-you, Jose
paul.mercer
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Re: The so-called "GKdos100"

Post by paul.mercer »

thanks Jose,
it makes fascinating reading, even though some of it is a bit much for me to understand, I'm sure it will provoke a lot of correspondence!
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Re: The so-called "GKdos100"

Post by spicmart »

Would that be okay if I share this in/on another group/forum?
I better ask for permission first.
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Re: The so-called "GKdos100"

Post by José M. Rico »

spicmart wrote: Thu Sep 09, 2021 6:37 pm Would that be okay if I share this in/on another group/forum?
I better ask for permission first.
Sure, no problem.
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Re: The so-called "GKdos100"

Post by José M. Rico »

OK, since nobody has commented much on the GKdos100, I will go first.

In the document, there is a comparison example between the battleships “Warspite” and “Bayern” both having 15 inch guns. It is interesting to note that according to the calculations within, the British gun can penetrate Bayern's barbette (350 mm thick) up to 24,300 meters, while the German gun can penetrate Warspite's barbette up to "only" 22,700 meters despite having considerably thinner armor plates (254 mm thick).

When comparing the shells used by both guns. the Germans assume the British 38.1 AP shell weights 875 kg and has a muzzle velocity of 745 m/s. On the other hand, the German 38 cm AP shell is lighter at 750 kg, but has a superior muzzle velocity of 800 m/s.
So, what is going on here? The article attributes the disparity in penetration power to the fact that the German gun is older than the British, and its AP shell is of an obsolete design.

So, I checked the penetration curves for the newest "38 cm SK C/34" gun of 800 kg and MV of 820 m/s, and its penetration power is slightly better than the British 38.1 cm gun, and of course much better than the old German 38 cm gun. In the comparison table between Bismarck and Royal Sovereign (Booklet h). The British 38.1 cm gun can penetrate Bismarck barbette (340 mm thick) up to 25,100 meters, while Bismarck "38 cm SK C/34" gun can penetrate RS barbette (254 mm thick) up to more than 30,000 meters, and Nelson's barbette (380 mm thick) up to 24,000 meters.

All this demonstrates how much a difference in armor penetration could be made by modern shell design with heavier and stronger piercing caps.

All the best to all.

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Byron Angel
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Re: The so-called "GKdos100"

Post by Byron Angel »

The trends I see in AP projectile design between WW1 and WW2 are: (a) slightly shorter shell body with a blunter head; (b) much heavier cap; (c) much longer and more streamlined overall shape. Over the course of 20-30 years, streamlining seems to have been advanced from 4crh heads up to 5/10crh, which implies respectably greater retained down-range striking velocity.

My assessment, FWIW.

B
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Re: The so-called "GKdos100"

Post by Steve Crandell »

Byron Angel wrote: Tue Sep 14, 2021 1:59 am The trends I see in AP projectile design between WW1 and WW2 are: (a) slightly shorter shell body with a blunter head; (b) much heavier cap; (c) much longer and more streamlined overall shape. Over the course of 20-30 years, streamlining seems to have been advanced from 4crh heads up to 5/10crh, which implies respectably greater retained down-range striking velocity.

My assessment, FWIW.

B
Yes, and also better performance when hitting at oblique angles.
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Re: The so-called "GKdos100"

Post by José M. Rico »

The following article by B. Hoyer is a very good complement to the GKdos100.

https://www.kbismarck.com/hoyer-warship-armor.html
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Re: The so-called "GKdos100"

Post by RobertsonN »

As I understand it in Gkdos100 Vol. a the Germans used ballistic data from WW1 for their first 38 cm gun and its 750 kg APC shell. For the penetration calculations they used material available in the late 1930s for the L4.4 series of shells. Because of this the calculations involved a shell that never existed, a 750 kg APC of the same external shape and ballistic properties as that earlier shell but with the superior metallurgical properties of the the later 38 cm APC. On the other hand, the ballistics of the British 15 in shell appear to have been calculated by the Germans assuming it had similar ballistics to those of the latest family of German shells. This meant that the British shells lost velocity less quickly and so struck belt and barbettes at a shallower angle than any WW1 era shells. This is another reason for the excellent showing of the British ship on the barbette penetration calculation. Similarly, both ships were in a form that never existed, i.e. they had the original design but with the later, considerably, improved armor quality. The only exception was that the armor deck in Bayern had been increased to 70 mm Wh to compensate for there now being no coal bunkers in Bayern which was here supposed to have oil fired boilers.

The penetration curves used for KC n/A and Wh were both three penetrations out of three hits curves and not median curves. This means that shells usually penetrated although not always. As such, a percentage of shells could also penetrate in somewhat more unfavorable conditions. These curves somewhat favor the ships.

While this set of assumptions considerably favored the British ship the calculations for the hit probabilities were markedly to the advantage of the German ship at ranges up to about 15000 m. Over about 20000 m it was the British gun that was significantly more accurate. These characteristics arose from the light shell/high muzzle velocity of the German gun.

The simple KE formula used favors the shell a bit where it first goes through KC armor. This is because a heavy plug is thrown out the belt, which absorbs some of the kinetic energy of the shell thus reducing its velocity. On the other hand, the plug is an extra projectile which causes damage inside ship. In addition, the Wh curves used for the armor deck are those for the capped shell. The uncapped shell had a reduced penetrative ability because of its reduced mass and more pointed head shape without the cap. Deflections on penetrating the outer layer of armor are also not included in this example. Deflection, dependent on plate thickness, always towards the normal to the plate, favors the shell for initial hits on the deck and the ship for initial hits on the belt. The possibility of yaw in a layered deck system is mentioned. But, apart from saying that the upper penetration limit will move upwards when a shell has to go through a plate with a greater cross-section, this possibility is not factored into these calculations. However, as the same assumptions are applied to both ships these simplified calculations did probably have some value,

Neil Robertson
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Re: The so-called "GKdos100"

Post by Thorsten Wahl »

The trends I see in AP projectile design between WW1 and WW2
The german L/3,7 Psgr(15 cm, 28 cm 38 cm),(except 30,5 cm) form a family of projectiles like the L/ 4,4...4,6 WW2 Psgr.

The WW1 / interwar L/3,7 projectiles can penetrate a caliber thick armour plate -quality KC(nA)- at around 570 m/s wheras the WW2 projectiles may penetrate through the same thickness at around 440m/s - 470 m/s.

the significantly larger armor piercing cap improved the performance against modern FH armour and also against homogenous armour at large angle of attack.

The reduced ogive improved durability of the projectiles during penetration in addition with improved hardening and mechanical properties.
Last edited by Thorsten Wahl on Sat Sep 18, 2021 7:56 pm, edited 1 time in total.
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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Re: The so-called "GKdos100"

Post by Thorsten Wahl »

Relative performance of KC aA(WW1) and KC (nA)(WW2)

At thickness 200 mm vs 15 cm Psgr L/3,7
Gg (Grenzschuss)at 0 degrees obliquity

KC(nA)approximately 740 m/s
KC(aA) approximately 680 m/s

The ballistic difference seems more marked at thicker plates.
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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