Vertical Penetration Estimates from British Trials

[rexford]

The British report on "German 75mm and 88mm APCBC Ammunition at Oblique Angle", Department of Tank Design Report No. M.6914A/4 No.1 provides test data at 45 and 55 degrees from vertical. Converting the data to performance against vertical armor provides some interesting insights into relative effectiveness.

A graph in the report presents the following penetration figures for 88mm APCBC, which are then converted to performance at the Tiger and Tiger II muzzle velocities (2558 and 3280 fps) against vertical plate using U.S. slope effect curves and the DeMarre equation:

=========================

88mm Large HE Capacity APCBC

65mm at 55 degrees & 2750 fps => 135mm at vertical and 2558 fps

58mm at 55 degrees & 2310 fps => 150mm at vertical and 2558 fps

62mm at 45 degrees & 2060 fps => 139mm at vertical and 2558 fps

Average = 141mm vertical at 2558 fps

=========================

88mm Small HE Capacity APCBC

81mm at 55 degrees & 2965 fps => 160mm at vertical and 2558 fps

76mm at 55 degrees & 2887 fps => 154mm at vertical and 2558 fps

57mm at 55 degrees & 2220 fps => 156mm at vertical and 2558 fps

Average = 157mm vertical at 2558 fps

=========================

Note that the small capacity 88mm round outpenetrates the large capacity ammo by about 11%.

Following converts small capacity data to 3280 fps muzzle velocity of 88L71 gun:

=========================

88mm Small HE Capacity APCBC

81mm at 55 degrees & 2965 fps => 228mm at vertical and 3280 fps

76mm at 55 degrees & 2887 fps => 220mm at vertical and 3280 fps

57mm at 55 degrees & 2220 fps => 223mm at vertical and 3280 fps

Average = 224mm vertical at 3280 fps

=========================

Curves are presented for 17 pdr APCBC penetration vs velocity against 45 and 55 degree plate (2900 fps is muzzle velocity of gun firing APCBC):

===================

17 pdr APCBC Solid Shot

82mm at 55 degrees and 2900 fps => 209mm at vertical and 2900 fps

100mm at 45 degrees and 2850 fps => 182mm at vertical and 2900 fps

===================

Notable that 17 pdr APCBC is not going to pierce the Panther glacis on other than an occasional hit at 100m and beyond, if hits take place on level ground and do not strike highly vulnerable spots (weld lines, MG mount and ball, driver visor area).

The penetration data at 55 degrees results in a vertical estimate which appears to be high, while the 45 degree figure is in line with published figures against vertical armor.

17 pdr APCBC appears to outpenetrate large capacity 88mm APCBC at 45 and 55 degrees by a considerable amount, which may be due to the following combination of factors:

1. solid shot vs HE burster yields greater penetration at all angles

2. British claim 17 pdr APCBC projectile nose is harder, increasing penetration

Data is also presented for German 75mm very small HE capacity APCBC:

=============================

75mm Very Small HE Capacity APCBC

58mm at 55 degrees and 2440 fps => 138mm at vertical & 2460 fps

62mm at 45 degrees and less than 2099 fps => above 130mm at vertical & 2460 fps

=============================

The vertical penetration estimates for 75L48 APCBC at 2460 fps are consistent with the figures developed using the German equations presented in the BIOS report, while the penetration figures for small capacity 88mm APCBC are lower than the BIOS material predicts.

Jeff Duquette deserves much credit for finding the abovenoted British report and pointing others toward the valuable work.

[rexford]

The following notes provide some additional details on the subject firing tests:

1. report is held by the British Public Records Office (PRO)

2. U.S. armor slope curves are based on an analysis of slope effect vs impact angle and T/D ratio (plate thickness/projectile diameter)

3. Projectile weights and HE burster capacity is as follows:

88mm large capacity APCBC: 9.6 kg and 1.65% of weight is HE filling

88mm small capacity APCBC: 10.1 kg and 0.65% of weight is HE filling

75mm very small capacity APCBC: 6.8 kg and 0.20% of weight is HE filling

Report indicates that large capacity 88mm ammo is used by Flak 36 and Tiger guns, whereas small capacity is fired by Tiger II and Pak 43. Other references have Tiger I firing small capacity 88mm rounds (German ballistic tables list 88L56 APCBC at 10 kg weight, with 10.2 kg for 88L71 APCBC).

4. 88mm projectiles are single piece monobloc (the main projectile body) whereas 75mm APCBC is two piece with a welded on nose.

5. U.S. firing tests with welded nose projectiles indicated that the round was superior to monobloc rounds at high impact angle, since the nose would break off and allow the ammunition to penetrate intact (single piece rounds would suffer much nose damage, increasing the limit velocity above the two piece rounds).

However, past discussions on welded nose German APCBC indicated that 75mm APCBC two-piece shells were heat treated in such a manner that the welded nose did not result in superior performance at high angle (Jeff Duquette contributed the welded nose info if I am not mistaken).

The British firing tests with 88mm and 75mm APCBC suggest that German welded nose ammo had about the same sloped armor performance as one piece projectiles would have.

[rexford]

Some time ago Jeff Duquette shared a graph with me that provided penetration figures for 17 pdr APCBC at angles from 0 to 70 degrees, with extrapolation to 75 degrees (rolled homogeneous armor). The vertical penetration is a bit higher than we estimate, 187mm vs 177mm at 0m.

The British penetration figures were presented to 600, 1000 and 1500 yards and we extrapolated the data to 0m and 2900 fps impact velocity.

The following analysis compares the slope effects for the British data at 0m with the estimates generated by our equation for U.S. APCBC slope effect:

0 degrees, 187mm penetration, 1.00 slope effect

20 degrees, 173mm penetration, 1.08 actual and 1.11 predicted slope effect

30 degrees, 150mm penetration, 1.25 actual and 1.29 predicted

40 degrees, 115mm penetration, 1.63 actual and 1.59 predicted

45 degrees, 101mm penetration, 1.85 actual and 1.82 predicted

50 degrees, 88mm penetration, 2.13 actual and 2.12 predicted

55 degrees, 77mm penetration, 2.43 actual and 2.51 predicted

60 degrees, 66mm penetration, 2.83 actual and 2.97 predicted

65 degrees, 56mm penetration, 3.34 actual and 3.36 predicted

70 degrees, 50mm penetration, 3.74 actual and 4.41 predicted

=============================================

Extrapolated penetration data at angle:

75 degrees, 38mm penetration, 4.92 actual and 5.22 predicted

The 17 pdr APCBC slope effects follow the U.S. curve fairly closely except at 70 degrees.

17 pdr APCBC penetration at 55 degrees and 0m set at 77mm from British curves, compared to 82mm on curve in test report for German 75mm and 88mm APCBC at oblique angles. In the absence of a low probability success (or hits on weld line, machine gun port, previous hit gouge, etc.), 17 pdr APCBC will not penetrate Panther glacis at any range on level ground.

Our analysis of flaw effect for Panther glacis versus 17 pdr APCBC indicates a 0.95 multiplier, which improves British gun performance a little but still results in low success probability.

[rexford]

The British report indicates that at 45 and 55 degrees impact, none of the German rounds penetrated in a condition where the HE burster would work. So, at high angles the German HE filled ammo was just like a solid shot except for the loss of penetration and added work that the HE filler entailed.

[rexford]

Some time ago Miles Krogfus shared a number of British Ordnance Board graphs with me for German 50mm APC, 75mm very small capacity HE APCBC and 88mm APCBC with small and large HE capacity.

Going back over the graphs after estimating the vertical penetration of 75mm and 88mm ammo from trials at 45 and 55 degrees, the graphs are in close agreement with the estimates from oblique hits:

VERTICAL PENETRATION ESTIMATES

75mm small capacity APCBC at 750 m/s (PzKpfw IVH muzzle velocity)

137mm from oblique hit

140mm from British O.B. curve

88mm small capacity APCBC at 780 m/s (Tiger muzzle velocity)

157mm from oblique hits

157mm from British O.B. curve

88mm large capacity APCBC at 780 m/s (Tiger muzzle velocity)

141mm from oblique hits

138mm from British O.B. curve

88mm small capacity APCBC at 1000 m/s (Tiger II muzzle velocity)

224mm from oblique hits

220mm from British O.B. curve

==========================

50mm APC at 2240 fps (PzKpfw IIIG muzzle velocity)

76mm from British O.B. curve

50mm APC at 2700 fps (PzKPfw IIIL muzzle velocity)

99mm from British O.B. curve

The consistency of the British Ordnance Board curves with the estimates from oblique hits suggests that the O.B. curves may have been based on firing tests.

[Grond]

I'm sure this got discussed to death long ago but the armor and penetation values in this game are nowhere near anything I've ever seen in 25 years of wargaming as well as looking at tests similar to the one you posted. I would love to see battlefronts official comment on this. Its hard to figure out how a Panther can weigh 50% more than a Sherman but only have 20% more armor. I also had the same reaction as you when I saw the figures for the 17pd gun. They also gave the 90mm gun more penetration than I've ever seen before as well as giving the Perhsing substantially more armor. Once again how can the Pershing weigh less than a Panther and have a lot more armor.

[flamingknives]

Grond, I can hardly claim to be an authority on the subject, but I can at least put forward some suggestions

Its hard to figure out how a Panther can weigh 50% more than a Sherman but only have 20% more armor.

Define armour. Do you mean armour mass?

Remember that the Panthers main armament is somewhat larger than the short 75 on a Sherman

Engine? Tracks? Ammunition? These all add to the mass of a vehicle and are not necessarily the same from one tank to another

They also gave the 90mm gun more penetration than I've ever seen before...

Well where have you seen it? I'm sure BFC/BTS would be interested in your source.

...as well as giving the Perhsing substantially more armor. Once again how can the Pershing weigh less than a Panther and have a lot more armor

Perhaps the Pershing is smaller. I've not seen a Pershing in real life, but I have seen a Panther, and they are really quite big. Again, define armour. The only way to compare armour to overall mass is to find what proportion of the mass is armour. IIRC, CM does not provide this info in the data screen.

The penetration and armour figures used in CM are taken from a variety of historical sources, including original documents.

Figures in tabletop wargames are frequently 'fudged' due to inadequate research facilities or simplifications to make them play better.

[Grond]

I've been looking since yesterday but haven't found it yet. Whoever did the Real Red mod for Close Combat 3 had posted some great information mainly from tests by the US Army but from other sources as well. The 90mm was a great improvemnt but did not even have the peneration of the German 75mm L70 and was no where near the 88mm L71. The same can be said for the British 17pd gun. The actual armor figures do jibe and are easy enough to find. The effect of slope should be easy to calculate but I noticed they gave US tanks and German tanks the same armor quality, I don't think this was the case. I've always heard the steel used in German armor was superior to American steel. What is even more puzzling though is that even using the figures in the game a Sherman should not be able to knock out a Panther with a front shot except for the occasional weak point (which seems to happen more often than it should). However I have seen Shermans penetrate Panthers with surprising regularity. I did see one post by rexford that seemd to prove that the projectiles used in German rounds were superior to the projectiles used by the Allies. When you add together these small differences in armor and penetration the effect on the game is huge. Allied tanks that could not penetate german tanks at all can now pentrate. Tanks that could only penetrate at close range can now pentrate at medium range and tanks that could penetrate at medium range can now penetrate at long range. While the mechanics they used for penetation are the most sopisicated I've ever seen the result flies in the face of every computer and board game I've ever seen on the subject as well as the real life accounts I've read. I can't help but wonder if they deliberately fudged some crucial data like armor quality, projectile velocity and projectile quality to appeal to American gamers.

[ August 31, 2003, 11:47 PM: Message edited by: Grond ]

[Grond]

Well I may have gotten a little carried away there. I'm sure there must be some grognards on this board that are more knowledgable on the subject than me. Am I wrong?

[Sir Uber General]

"What is even more puzzling though is that even using the figures in the game a Sherman should not be able to knock out a Panther with a front shot except for the occasional weak point (which seems to happen more often than it should)."

I'm afraid you are wrong, the above report says cannot penetrate the glacis,

"17 pdr APCBC will not penetrate Panther glacis at any range on level ground."

That leaves the turret front and lower hull front available for a kill shot from the frontal aspect.

Furthermore I think the CMBO penalises late war panzers with a -% armour modifier as quality was not so good at that stage. I think that kicks in from panther G onwards.

[Grond]

Thanks for the reply. If you look at the scenario Battle in the Shadow the Panther A and Panther G are both rated at 85% and Marder 2 and 3 are rated at 95%. The Shermans are all rated at 85% but the Cromwell, Churchhill, Sexton, Kangaroo, Wolverine. Obviously any Western Front engagment is going to be late war but I was under the impression the quality only went down very late. I haven't been able to locate anything recently on penetration tests other than the info posted on this board yet. If anybody has some links I'd appreciate it. Specifically I'm looking for data on the 76mm and the 17pd gun. This post and soem other posts about the 76mm seem to indicate they both have more penetration than they should. While I do think the 90mm is also a little off its not really a big deal since it should rarely see action. I haven't seen any responses by BTS on any threads though. As for the 17pd gun vs the Panther going by the in game figures it can penetrate the lower hull to almost 500m and the turret to almost 2000m.

[ September 01, 2003, 01:04 PM: Message edited by: Grond ]

[flamingknives]

There is a slight misrepresentation of armour in CMBO, as I don't think code to represent curved armour was introduced until CM:BB.

This effect would greatly strengthen the side turret of the Tiger and the front turret of the Panther.

Also, both the 76mm and the 17pr have tungsten cored rounds (APCR and APDS, respectively) which will greatly improve the penetration of said guns. the inaccuracy of the 17pr APDS is not modelled, however.

I've always heard the steel used in German armor was superior to American steel.

This could do with a source or somesuch, or even just a clarification of how it was 'better' The Panther front glacis is a very large lump of metal, and such things are not easy to make well

[Grond]

Thanks for the tip, I'm still catching up, I haven't been to this board in a couple years. I noticed tungsten is not effective at high angles but does seem to be the only choice in some situations when your only chance is penetrating the turret with tungsten. How big was the accuracy difference between regular ammo and discardng sabot? Was that particular to the 17 pdr or did it effect the other guns as well?

[ September 02, 2003, 07:10 AM: Message edited by: Grond ]

[Grond]

[flamingknives]

How big was the accuracy difference between regular ammo and discardng sabot? Was that particular to the 17 pdr or did it effect the other guns as well?

AFAIK, it was particular to the 17pr. and possibly the 6pr. in WWII, as these were the first and only (of their period) full-bore guns using Discarding Sabot (APDS) shot. Other guns with tungsten ammo used full sized shell with a tungsten core.

I counld't tell you how big the inaccuracy effect is, John Salt would be your man for that.

It's been a while so I couldn't tell you where I read that but I also heard the same thing about the German Battleships and Pocket Batleships on the history channel, that they had higher quality steel.

Ah, but battleship armour and AFV armour are a whole different kettle of fish.

Plus the Panther was made 1943-45, whereas the German battleships were built pre-war in most cases, where there was less pressure on the manufacturing processes.

It could be a reference to the fact that the Germans used Face-hardened armour on a wide basis on the early mk3 and mk4 Panzers.

If yopu do a search on the CM:BB forum for rexford's membership number, you should find a wide variety of discussions on armour, shells, face-hardening and more.

[Grond]

Has Battlefront commented on the penetration of the 17 pdr and 76 mm?

[flamingknives]

Not that I've seen.

AFAIK, no-one has ever provided contrary evidence.

[Grond]

I finally found the John Salt document and it does appear that the 30 degree slope penetrations used in CM are pretty close to the ones he lists. Rexford appears to have ultilzed the actual firing tests in the book he did with Livingston as well as accounted for the factors that led to differing results, did CM utilize his figures for the game? However this statement does not equate with my game experiences:

Originally posted by rexford:

Notable that 17 pdr APCBC is not going to pierce the Panther glacis on other than an occasional hit at 100m and beyond

It can't be attributed to tungsten rounds since they actually have less penetraton at that angle. I have seen mentioned that if the penetration is less than the armor thickness it may still penetrate at a lower probablility if the difference isn't too great. This is obviously true if you think about it but I didn't take it into consideration in what to me were some surprising results. I'd like to find some more info on that. I've also seen some penetration charts showing the probability of a kill at different angles, are these avilable in game?

[flamingknives]

However this statement does not equate with my game experiences:

</font><blockquote>quote:</font><hr />Originally posted by rexford:

Notable that 17 pdr APCBC is not going to pierce the Panther glacis on other than an occasional hit at 100m and beyond

It can't be attributed to tungsten rounds since they actually have less penetraton at that angle.</font>

[rune]

1. The game does NOT use a lookup table for the effect for penetration. It uses a modified mathimatical formula that Charles coded.

2. Rexford is on the beta team, and for a large part, agree with the numbers listed, but he can answer that on his own.

3. The game generated enough interest do get people to dig deeper into the research.

Rune

[MrSpkr]

Well, I haven't really done too much in the way of vertical penetration; however, I consider myself an expert in horizontal penetration. Why, once when I was driving back to college after spring break . . umm, wait.

Different subject. Never mind.

Steve

[Dandelion]

Rune,

Would there be any possibility of seeing the mathematical formula? Not as in code, but as translated into a ballistic formula.

Aslo, while I (might) have your attention, do you know of any such formula for spotting? That could be presented, so one would know ranges and factors affecting spotting etc?

Regards

Dandelion