Medium thickness KC/n.A. -comparative data

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delcyros
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Medium thickness KC/n.A. -comparative data

Post by delcyros » Thu May 24, 2012 1:45 pm

When considering the protective value an the merits of medium thickness KC/n.A. armour, such as installed in BISMARCK´s upper side belt (145mm), turret slope (180mm) or barbettes, turret´s and CT of the ADMIRAL HIPPER class, little actual cross reference data i aviable.

The most important primary source detailing this issue is AD-955-281, Ballistic Test and Metallurgical Examination of Japanese Heavy Armour, Report No. 5-47, dated to November 1947.
Material located in Kure was shipped to the U.S.N.P.G. Dahlgren and subjected a series of comparative trials to asess their metarial properties compared to contemporary US armour plate.

Cross country tests of german, japanese and US face hardened and homogenious armour are entailed in this report. The data have been assembled with help of the following primary sources:
[1] Extract of Japanese Armor Required for United Kingdom
for Examination.

[2] NPG ltr A8-2(3)EF37(BPO 97993) dated 25 June 1946.
[3] BuOrd ltr EF37(Re3a-G3) dated 15 August 1946.
[4] U. S. Naval Technical Mission to Japan Report
"Japanese Heavy Armor" dated January 1946.

[5] Hardness Conversion Chart for Hardened Steels
H. Scott and T. H. Gray.

[6] NPG 2.tr A8-2(3)EF30(P 70245) dated 25 February 1947.

Here we are confronted with a certain condition of test, which for our subject of interest included two roughly similar projectiles, the 335lbs US super-heavy 8in Mark 21 MOD 3 and the similar sized, similar heavy 8" Mk 21 MOD 5. This projectile was entirely comparable to the former but had a specially hardened armour piercing cap with 650 to 680 Brinell all the way through instead of 550 to 560 Brinell surface cap hardness of the mod 3 AP also used in these trials.

One need to be careful when extrapolating the results of cross country trials. Details like those mentioned above may turn out to be very important differences. The harder armour piercing cap appearently improved penetration through deep chilled face hardened armour, such as contemporary US class A armour, which typically had 55% face depth compared to 35% for Vickers hardened armour plates made by the japanese.

Japanese VH armour typically was found subpar to US class A when attacked by 8in APC at 30 degrees obliquity (no other condition was trialed, 30 degrees was a standart proofing test condition for acceptance of US armour plate and armour-piercing-projectile).
However, one plate, JE-50-3133 was different to other armour plates taken from Kure.
This 7.25" plate (nominal, actual thickness at impact point was 7.21 and 7.22in), among the thinnest japanese VH samples mentioned in Report 5-47 had a deeper chill than normal VH armour, about 40 to 42% with a very linear drop in hardeness to the back and in this was found to be very similar to captured german KC/n.A. armour plates in this thickness range but unlike those, this experimental japanese Vickers Hardened plate had no cementated layer at the face.

When tested against the 335lbs US 8" mark 21 mod 3 at 30 degrees, the % NBL of Ord. Sk. 78841 was 117 to 119 (=118 +-1) and compared favourably with the 1944 to 1947 US average class A plate figure of 112.8 (4.6% superior to average US class A) and was found even slightly better than an experimental non cementated US class A armour plate. The actual impacts were:

[1] impact 33402 at 29.4 degrees obliquity with 1808 fps velocity (116.4% Ord. Sk. 78841), Incomplete penetration, nose chewed off, base slap, body upset
[2] impact 33403 at 29.3 degrees obliquity with 1867 fps velocity (120.5% Ord. Sk. 78841), complete penetration, nose chewed off, body extruded, 3/4 base off, prokjectile not in effective bursting condition.


In addition, this armour plate heavily damaged the projectile during penetration and was the only armour plate capable of damaging the virtually indestructable US super heavy APC. When the projectile, however, was changed to 8in Mark 21 mod 5 striking at 30 degrees obliquity, with it´s super hard armour-piercing cap, it penetrated through intactly at average of 110.5 % NBL of Ord. Sk. 78841, again comparing favourably with the 1944 to 1947 US average of class A plate of 109.7 (.7% better than it). Only one 7.6" US class A Carnegie manufactured, experimental armour plate No. 1G469A1 with no cementation layer applied achieved an NBL ~1826 fps @ 30 deg (112 to 113% NBL of Ord. Sk. 78841 for this thickness, projectile and obliquity) slightly higher than this armour plate. The actual impacts with mod 5 were:

[1]impact 33396 at 29.4 deg with 1627 fps (104.2% Ord. Sk. 78841), Incomplete penetration, nose chewed off, base slap
[2]impact 33398 at 29.3 degrees with 1787 fps (115.4% Ord. Sk. 78841), Complete penetration, projectile effective with sides slightly gauged
[3]impact 33399 at 30.0 degrees with 1706 fps (109.3% Ord. Sk. 78841), Incomplete penetration, nose chewed off, 1/3 base ring torn off, projectile effective
[4]impact 33401 at 30.2 degrees with 1748 fps (111.6% Ord. Sk. 78841), Complete penetration, projectile effective with sides gauged and nose cracked

In addition to this very spectacular performing japanese armour plate, a german medium thickness, 215mm KC/n.A. armour plate No. 33032 was subjected to ballistic trials in the U.S.N.P.G. Dahlgren. This plate had a face thickness of 44% with a thin, cementated layer applied to the surface with no drop in hardness through the thin, cementated layer. In light of the experience with deep chill armour, no trials with 8" mark 21 mod3 APC were attempted. The trials fully concentrated on 8in mark 21 mod 5 APC with their specially hardened armour piercing caps. It was established that 2,026 fps striking velocity at 30 deg were required to completely penetrate the plate, representing an 113% NBL of Ord. Sk. 78841 for the projectile, obliquity and plate thickness.
The projectile was not much damaged in the process, as could be expected by use of the 650 Brinell hardened armour piercing cap.

That beeing said, this non-experimental KC/n.A. armour plate was found to be +3.2% better than average, 1944 to 1947 manufactured US class A armour plate (which in it´s own regard according to Revision "J" was considered to be ~2.5% better than 1935 to 1943 manufactured US-class A face hardened armour plate). it was also slightly better (+0.9%) slightly better than the experiemental Carnegie US class A plate and by +2.3% better than the outstanding japanese armour plate tested there.

Since the Carnegie plate No. 1G469A1 was not only trialed against the mod 5 but also against the mod3 and had a an elevated NBL 116 to 117% Ord. Sk. 78841 it´s also possible to calibrate the KC/n.A. plate No. 33032 with 8in mark 21 mod3 projectiles. Thus, a very good case can be made claiming that this medium thickness range KC/n.A. armour plate was the best armour plate ever tested in this thickness range at the U.S.N.P.G. Dahlgren against 335lbs 8in mark 21 mod 3 & 5 APC at 30 deg. It´s entirely understandable why they didn´t even attempted to test it against the mark 21 mod 3...

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Herr Nilsson
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Re: Medium thickness KC/n.A. -comparative data

Post by Herr Nilsson » Thu May 24, 2012 2:16 pm

delcyros wrote:When considering the protective value an the merits of medium thickness KC/n.A. armour, such as installed in BISMARCK´s upper side belt (145mm), turret slope (180mm) or barbettes, turret´s and CT of the ADMIRAL HIPPER class, little actual cross reference data i aviable.
It's a bit off topic, but what if Bismarck's turret slope wasn't made of KC/nA but Wh?
Regards

Marc

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delcyros
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Re: Medium thickness KC/n.A. -comparative data

Post by delcyros » Thu May 24, 2012 8:33 pm

That's a good question. I don't know the answer. Do You happen to have indication for Wh applications on the slopes?
Though admittently, my concern here was the KC armoured turrets and barbettes of the HIPPER's primarely.
The 8inches gun trials don't allow conclusions to be drawn for large calibre impact but against cruiser size projectiles, I found the data in the Dahlgren trials kind of surprising. My previous estimate was that KC/n.A. was inferior to US class A against cruiser sized guns but in cross country trials they turned out to be slightly better and indeed much better than has been attributed previously.

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Herr Nilsson
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Re: Medium thickness KC/n.A. -comparative data

Post by Herr Nilsson » Thu May 24, 2012 8:37 pm

delcyros wrote:That's a good question. I don't know the answer. Do You happen to have indication for Wh applications on the slopes?
Yes, it seems to me that only the front plate was KC/nA. Everything else was Wh.
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Marc

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delcyros
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Re: Medium thickness KC/n.A. -comparative data

Post by delcyros » Fri May 25, 2012 4:36 pm

It´s possible that intact APC projectiles (those not stripped off their windscreens, hoods or AP-caps by previous impacts) will have somehow less penetration against thick homogenious armour than similar sized, similar heavy uncapped AP-schot.

Against thinner homogenious armour (such as is not capable of shattering the cap) the cap just changes the nose form, which may yield positive or negative results, depending on the change of ogive. AP with blunt shaped noses typically have an benefit at high obliquity but loose this at right angle´s impact.

This can make things complicated. While shattering the armour piercing cap, the projectile looses some energy (the cap is a poor substitue for the projectile nose). Against face hardened armour, the cap protects the nose of the projectile from shatter but destroys itselfe. Homogenious armour typically is not capable to damage much of even an uncapped projectile´s tip of the most advanced APC (unless the impact is against very THICK slabs of plate or highly obliquily so that the base can be damaged).

The GKdos-100 curves at least should allow some data against german intact projectiles, though I don´t know how to correlate that with the few data we have on other nations projectiles.
Againt the 38cm projectile, 180mm Wh are not penetrable at closer as or 100hm (640m/s and 61 deg resultant impact obliquity), at 150hm (570m/s and 59 deg resultant obliquity)or 200hm (510m/s and 52 deg obliquity). Though they appear to be penetrable at 250hm distance (470 m/s and 44 deg resultant obliquity).

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Re: Medium thickness KC/n.A. -comparative data

Post by Dave Saxton » Sun May 27, 2012 3:14 am

Againt the 38cm projectile, 180mm Wh are not penetrable at closer as or 100hm (640m/s and 61 deg resultant impact obliquity), at 150hm (570m/s and 59 deg resultant obliquity)or 200hm (510m/s and 52 deg obliquity). Though they appear to be penetrable at 250hm distance (470 m/s and 44 deg resultant obliquity).
Apply this data set to the KCnA curves and the differences between face hardened armour and homogenous armour at these obliquities is stark indeed. The design rationales and the trade offs are beginning to be much more understandable.
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