Wa Prüf data for 8,8cm KwK 36

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Avalancheon
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Wa Prüf data for 8,8cm KwK 36

Post by Avalancheon » 20 Aug 2019 08:03

In one of his books on the Tiger tank, Thomas Jentz provides a couple of tables for the 8,8cm KwK 36 gun. These tables were apparently based on documents from the Wa Pruf. They define what range a penetration could be expected against a certain aspect of a tank (hull front, turret front, hull side, turret side, etc). The figures are rather perplexing, though.

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The first table states that the 88mm gun could penetrate the Shermans nose from 2100 mt distance, but could not penetrate the DFP from any range at all! This is very strange indeed. The M4A3 Sherman had a 63mm thick glacis at 47 degrees, which should not offer any problem at all for this gun.

The second tables states that the 88mm gun could penetrate the IS-2s and T-34/85s nose from 300 mt and 100 mt distance, respectively. It also says that the DFP of both tanks could be pierced from the same range, which is 100 mt distance! This makes no sense at all. The IS-2 was much better armored than the T-34/85. It had a 120mm thick glacis at 30 degrees, whereas the T-34/85 had a 45mm thick glacis at 60 degrees.


Can anyone hazard guess at what is going on here? Why are the Wa Pruf figures so wildly off base? Did they actually perform ballistic tests against the tanks in question, or were they just making estimations? Another question is, what criteria did they use for a shell penetration? Did they have to punch through the armor fully intact?

critical mass
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Re: Wa Pruf data for 88mm kwk 36

Post by critical mass » 20 Aug 2019 19:40

The fire effect tables are computed with an additional 30 deg target angle. They assume similar plate quality as german reference plate.
Also take note, that they are based upon the more heavily uparmoured variants encountered. This at times, proves challanging to identify without additional information. However, its significant for the T34.

Avalancheon
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Re: Wa Pruf data for 88mm kwk 36

Post by Avalancheon » 24 Aug 2019 01:45

critical mass wrote:
20 Aug 2019 19:40
The fire effect tables are computed with an additional 30 deg target angle. They assume similar plate quality as german reference plate.
Also take note, that they are based upon the more heavily uparmoured variants encountered. This at times, proves challanging to identify without additional information. However, its significant for the T34.
I knew that the tables were based on a 30 degree obliquity, but not that they assumed a similar plate quality. I guess that could explain the oddity of the 88mm being unable to penetrate the Shermans DFP from any range *. However, it still doesn't explain why the T-34s glacis was regarded as equal to the IS-2s glacis!

*After all, the drivers front plate was thicker than the glacis (or nose) itself.

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critical mass
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Re: Wa Pruf data for 88mm kwk 36

Post by critical mass » 24 Aug 2019 08:09

The DFP= glacis in those tables.
My guess is that they may have based them on uparmoured variants of the Sherman / T34.
The fire effect tables point out that they are based upon the most heavily uparmoured variants encountered.

But anyways, the 30 deg additional target angle is critical here. This turns the 60 deg glacis of the t34 Into a very severe, 64 deg one and the 30 deg nose/ driver front plate of the IS2 obr.1943 into a 38 deg condition. And while the t34 armor base may be uparmoured, the IS certainly was not...

Remember, these tables were computed using G(D] graphs. Not tested actually.

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Re: Wa Pruf data for 88mm kwk 36

Post by Avalancheon » 26 Aug 2019 07:40

critical mass wrote:
24 Aug 2019 08:09
The DFP= glacis in those tables.
If true, that changes everything. The glacis itself cannot possibly be offering the level of resistance the Wa Pruf assumes.

When angled at 30 degrees, the M4A3 Shermans glacis would have a net obliquity of 53 degrees. Even with the assumption of similar quality plates, the 88mm gun should be able to penetrate that at moderate range. These tables must be in error.
critical mass wrote:
24 Aug 2019 08:09
My guess is that they may have based them on uparmoured variants of the Sherman / T34.
The fire effect tables point out that they are based upon the most heavily uparmoured variants encountered.
That doesn't seem likely. The T-34/85 had the exact same glacis armor as the earlier T-34/76. And the M4A3 Sherman was only slightly better armored than earlier variants.
critical mass wrote:
24 Aug 2019 08:09
But anyways, the 30 deg additional target angle is critical here. This turns the 60 deg glacis of the t34 Into a very severe, 64 deg one and the 30 deg nose/ driver front plate of the IS2 obr.1943 into a 38 deg condition.
Is the difference between 60 and 64 degrees really that significant? The T-34s armor is significantly overmatched by the 88mm projectile, after all. Some additional obliquity shouldn't really matter.
critical mass wrote:
24 Aug 2019 08:09
And while the t34 armor base may be uparmoured, the IS certainly was not...

Remember, these tables were computed using G(D] graphs. Not tested actually.
No variant of the T-34 had glacis armor equal to the IS-2. Not even close.

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Re: Wa Pruf data for 88mm kwk 36

Post by critical mass » 27 Aug 2019 16:25

Avalancheon wrote:
26 Aug 2019 07:40
critical mass wrote:
24 Aug 2019 08:09
The DFP= glacis in those tables.
If true, that changes everything. The glacis itself cannot possibly be offering the level of resistance the Wa Pruf assumes.

When angled at 30 degrees, the M4A3 Shermans glacis would have a net obliquity of 53 degrees. Even with the assumption of similar quality plates, the 88mm gun should be able to penetrate that at moderate range. These tables must be in error.

After putting the data into account, I can confirm that my explenation does indeed provide a rational answer to the problem at hand.
example (88mm vs Sherman A4 DFP):

53.06 deg compound netto obliquity for the 63.5mm (2.5") Sherman glacis (without upgraded or bolted on plating).
the penetration at of the 88mm KWK36 with Pzgr39 at 100m range was 120mm rated (at 30°).
according to official graphs of obliquity performance for 800m/s striking velocity,
penetration at 0°=1.23
penetration at 10°= 1.20
penetration at 20°=1.14
penetration at 30°=1.00 reference penetration of firing tables
penetration at 40°= 0.75
penetration at 50° =0.56
penetration at 60° =0.44

this makes penetration at 53.06deg roughly a factor = 0.525
0.525 x 120 = 63mm
63.0mm < 63.5mm

Thus, calculated penetration of the 88mm KwK36 at 100m distance against the Sherman DFP -if calculated this way(!)- was insufficient, if we follow the german firing tables.

Whether or not this bears relevance for practice depends largely upon the question how US RHA behaved at obliquity in comparison to reference german RHA test plate.

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Re: Wa Prüf data for 8,8cm KwK 36

Post by Avalancheon » 03 Sep 2019 15:56

What kindof criteria was the Wa Pruf using, though? Was this with the shell penetrating the armor in a condition fit to burst?

Regardless, it seems like a pretty narrow safety margin. The shell penetration is just equal to the plate thickness...


These slope multipliers seem to indicate that the Sherman had a better glacis than the Tiger (if they were of the same hardness)!

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Re: Wa Pruf data for 88mm kwk 36

Post by Mobius » 03 Sep 2019 20:12

critical mass wrote:
27 Aug 2019 16:25
53.06 deg compound netto obliquity for the 63.5mm (2.5") Sherman glacis (without upgraded or bolted on plating).
the penetration at of the 88mm KWK36 with Pzgr39 at 100m range was 120mm rated (at 30°).
according to official graphs of obliquity performance for 800m/s striking velocity,
penetration at 0°=1.23
penetration at 10°= 1.20
penetration at 20°=1.14
penetration at 30°=1.00 reference penetration of firing tables
penetration at 40°= 0.75
penetration at 50° =0.56
penetration at 60° =0.44

this makes penetration at 53.06deg roughly a factor = 0.525
0.525 x 120 = 63mm
63.0mm < 63.5mm
That is so close it deserves to go into a curve fitting program. The one I use comes up with 63.8mm.

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