Side angle, tactical anecdote, limits on conclusions

[JasonC]

I thought some might find interesting the following analysis I made of random side angles and their effects on conclusions drawn from tactical anecdotes about penetration possibilities.

The anecdote that got me thinking about the problem was about a couple of Tigers that found themselves in the midst of a formation of T-34/76s and were hit around 20 times without being penetrated. Some wanted to conclude from this that the 80mm flat side armor of the Tiger I was not penetrable by the 76mm at any range.

Over at the Russian battlefield site, meanwhile, they list the initial penetration of the BR-350B (capped) round as 84mm at 500m. Of course we do not know whether the capped rounds were available in the engagement in question. But assume it was.

The AAR reports the engagement ranges as under 1 km, from all directions.

So I asked myself - suppose I randomly distribute the firing locations in a 1 km circle around a Tiger I. Suppose the following side angles are needed to get a (partial) penetration -

within 10 degrees of flat at 500m

within 15 degrees of flat at 300m

within 20 degrees of flat at 100m

25 degrees and upward was assumed to be sufficient to defeat the round, regardless of range. Also, ranges beyond 500m were considered sufficient to defeat the round. Last, the portion of the target presented by the tracks and running gear was assumed to be -

30% from the side aspect

10% from the rear aspect

Under those assumptions, the chance that a random shooting location makes a penetration possible is 1 out of 26. The number of hits needed to have a 50 50 chance that 1 came from a spot where penetration was possible is 18 hits. The chance that 20 hits would fail to produce a single penetration, on the calculated chance per hit, is 46%.

You can see why as follows. 3/4 of the area within 1 km of the Tiger is the longer half of the range - 500 to 1000m. The inner half of the range is a quarter of the area.

The 100m range envelope is only 1/25th of the remaining 500m window. Of that 1/25th, 120 degrees of the circle, or 1/3rd, are within 20 degrees of flat to one or the other side, or the rear. The other 240 degrees of the cicrle have high side angle or face the front.

8/25s lie between 100m and 300m. Of that ring, 1/4 have side angles under 15 degrees (+15 to -15 on right side is 30, same left side, same rear, equals 90 out of 360 degrees).

16/25s lie between 300 and 500m. 1/6 of those have side angles of 10 degrees or less.

So overall, you have 1/3 of 1/25, plus 1/4 of 8/25, plus 1/6 of 16/25. Just for side angle - that is after the 1/4 factor for close enough range.

Range takes you down to 25%. Side angle eliminates 4/5th of those and takes you down to 5%.

Then 30, 30, 10 percent will hit the tracks, averaging 23.3%, leaving 76.67% to hit hull or turret. So you have another reduction of 1/1.3.

That takes you down to 3.83%, or 1 out of 26.

1 - 1/26 to the 18th power is .49. So it takes 18 independent random chances at 1/26 to get a 50 50 chance of 1. The same to the 20th power is .46.

What does all of this detail mean? It means you can't assume 80mm flat can't be penetrated, from an anecdote with random ranges and side angles. You need a test at *zero* side angle - tactically a very rare event - and at the specified range.

Random ranges tend to be medium to long. Actually they will be weighted even more heavily that way, because tanks closer in don't live as long. Similarly, they will tend to be weighted toward the front aspect - of the turret in particular - because the target tries to face its opponents.

But even without weighting the front and farther locations more heavily, just random weightings leave only a very small portion in the "vunerable lobes", close and flat side angle. You can get statistically very good protection without literal invunerability.

I hope this is interesting.

[Kirill S.]

so what you are saying is that the Tiger in CM is modelled as invulnerable against the T-34?

[JasonC]

Nearly so. APCR and a close shot will penetrate sometimes at close range. With the standard AP, the rated penetration is enough at 100m if the shot is flat, but in practice you just see "shell broke up" results. StuG fronts are similar, with 100m and under flat shots occasionally giving a partial pen, but usually "shell broke up" - and that is rated 95% quality, not 100% like the Tiger I.

[Kirill S.]

From what I hear, standard APCR wasn't used against Tigers all the time. The tankers preferred the subcaliber rounds (Tungsten?). what will be the result if the T-34s use t ammo only?

[StellarRat]

OK, here's a question, if the round can barely make it through the armor in the first place does it have enough energy to knock the tank out? It seems to me that a peneration with no UMMMPH behind would probably be far less dangerous than a round that goes through both sides of a tank. 1. I guess an explosive burster would make a real difference in this case. 2. Does CMBB take the post peneration energy of AP rounds into account?

[ April 19, 2003, 09:31 PM: Message edited by: StellarRat ]

[JasonC]

APCR stands for armor piercing composite rigid, and it a synonym for tungsten and for subcaliber. Tungsten is the alloy that makes it "rigid". It is called "subcaliber" because the tungsten core penetrator is smaller than the diameter of the entire round. APCR is not an APDS, discarding sabot round, however. Only the Brits had those in WW II. Everyone else's tungsten was APCR.

The Russian designation of the APCR round for the 76mm in the T-34 is the BR-350P. It is the "P" that designates it the tungsten core, APCR round. Plain AP without a ballistic cap was BR-350A. APBC with a ballistic cap was BR-350B. The B grips armor better, reducing skid off of face hardened plates in particular. In CMBB, the T ammo is the BR-350P. The standard AP numbers vary with date and are intermediate between the 350A and 350B figures at the Russian Battlefield site.

As for reduced behind armor effect for marginal penetrations, CM has the category of "partial penetration" exactly to cover those. A partial penetration can still lead to knock out, particularly when it comes from a large caliber round, a round with a large bursting charge, etc. But it is more likely to result in other types of damage - gun damage and crew loss on turret hits, or immobilization and crew loss on hull hits, or just crew loss and shocks, or sometimes "no significant damage". Those can happen on full penetrations as well, particularly with small caliber plain AP.

[John D Salt]

Originally posted by JasonC:

APCR stands for armor piercing composite rigid, and it a synonym for tungsten and for subcaliber. Tungsten is the alloy that makes it "rigid".

Not quite; "rigid" in this context means that that the emergent calibre of the whole projectile is the same as the initial calibre.

APCNR (Armour Piercing Composite Non-Rigid) is the third tungsten-cored nature to be used in WW2, as in the Maroczec AT rifle, the Gerlich squeeze-bore series of guns and the Littlejohn adapters.

All the best,

John.

[JasonC]

Aha, thanks for the correction John.

[PzKpfw 1]

concerning Soviet ammo designations below is terminology from Soviet WW2 records on ammo designations:

AP shot - Normal AT round.

APS - Supercharged AP shot. Higher IMV.

Podkaliberniy - sub-calibre,tngsten carbide core. More commonly refered to as HVAP in the west, sub-calibre hypervelocity round.

SAP - Semi-Armor piercing, Naval round developed for Artillery. Ie, the M1910/30, M1910/34, 152mm Gun/Howitzer, as well as the M1938, & M1943 152mm Howitzer's fired SAP rounds.

Below is a list of WW2 Soviet KE penetrators i have compiled with DOI where known:

BR-167 - 37mm - 1939

B-240 - 45mm - 1941

BR-243P 45mm - 1942

BZ-240 - 45mm - 1941

BR-271 - 57mm - 1943

BR-271K - 57mm - 1943

BR-271P - 57mm - 1943

BR-271SP - 57mm - 1943

BR-350 - 76mm - 1939

BR-350A - 76mm - 1940

BR-350B - 76mm - late 1942 early 1943

BZR-350B - 76mm - 1942

BR-350P - 76mm - 1943

BR-365 - 85mm - 1943

BR-365K - 85mm - 1943

BR-365P - 85mm - 1943

BR-412 - 100mm - 1944

BR-412B - 100mm - 1944 (late)

BR-471 - 122mm - 1943

BR-471B - 122mm - 1943

Soviet KE penetrators were manufactured in both solid core, & with an small HE cavity. The rounds had an short ogive & a blunt nose with an thin ballistic windsheild. After WW2 they developed an blunt noseed, AP capped round with an ballistic windsheild.

The main difrence in the WW2 Soviet full-calibre KE projectiles,from other nations similar type ammunition, was the Soviet rounds used grooves located either in front of, or at the bourrelet.

These grooves were described as localizers made to prevent the HE filler from failing upon impact, so that the round delivered its full explosive power behind the armor in the targets fighting compartment.

The Soviet's because of the increasing armor thickness of German tanks as well as after studying captured German PzGr.40 APCR ammunition developed sub-calibre or spindle ammunition. The spindle ammunition was designed in Febuary 1942 & accepted for service production on April 1 1942.

The first Soviet sub-calibre round issued was the 45mm BR-243P round. 2 designs for the new 45mm spindle round were submitted 1 round was ballisticly superior in that it caused less barrel wear, but it was not accepted, for service because, it required complicated manufacturing methods & used more material.

The BR-243P was very effective vs German tanks at ranges from 500 - 1000m, Soviet reports state the BR-243P was as effective as solid shot to a range of 1000m but at ranges above 1000m accuracy was severly affected.

By 1943 the Soviets had developed 2 more spindle rounds the 57mm BR-271P & the 76mm BR-350P. The Soviets basicly copied examples of the 76.2mm German APCR round that he Germans had made for captured Soviet 76.2mm feild gun.

Concerning German Arrowhead ammunition the German PzGr.40 APCR ammunition originaly used an solid aluminum and/or magnesium windscreen, to achieve an behind the armor incendiary effect after the round had penetrated the plate.

The reason for the windscreen was based on Polte's work on shell carrier crush up studies. Later in the war as material shortages became prevailent the Germans used plastic or thin steel for the windscreens.

The Soviets also adopted the use of aluminum windscreens on some of their KE rounds but their is no evidence they were aware of the behind the armor incendiary effect. Soviet data explains the use of the ballistic windsheild in causing an high temprature spalling and an shock heated particle effect from the fractured penetrator core.

Regards, John Waters

[ April 21, 2003, 04:51 PM: Message edited by: PzKpfw 1 ]

[Amedeo]

John,

I'm curious about the BR-412B and BR-471B rounds' DOI you listed. AFAIK the recent consensus is that the 100mm APBC didn't saw actual action during WW2 and the 122mm APBC was used only in spring 1945.

Regards,

Amedeo

[PzKpfw 1]

Originally posted by Amedeo:

John,

I'm curious about the BR-412B and BR-471B rounds' DOI you listed. AFAIK the recent consensus is that the 100mm APBC didn't saw actual action during WW2 and the 122mm APBC was used only in spring 1945.

Regards,

Amedeo

Hi Amedeo, concerning the 100mm BR-412B in past discussions ppl were adamant the 412B entered production Nov/Dec 1944,

so I added it. It originaly wasnt on my list BTW, my data stated a much later DOI. Ie, Backoffen & Williams both give the DOI of the BR-412B, as 1955, while 1 US Army Soviet threat pamplet lists the BR-412B DOI as 1954 etc.

Concerning the BR-471B Zaloga, Backhoffen etc, all show a late 1943 DOI, and as it was used in WW2, I added it.

If you have more recent data Amedeo pls feel free to correct any errors, so I can modify the list.

Regards, John Waters

[ April 21, 2003, 05:56 PM: Message edited by: PzKpfw 1 ]

[rexford]

Jason C started off the thread by saying: " I thought some might find interesting the following analysis I made of random side angles and their effects on conclusions drawn from tactical anecdotes about penetration possibilities.

The anecdote that got me thinking about the problem was about a couple of Tigers that found themselves in the midst of a formation of T-34/76s and were hit around 20 times without being penetrated. Some wanted to conclude from this that the 80mm flat side armor of the Tiger I was not penetrable by the 76mm at any range.

Over at the Russian battlefield site, meanwhile, they list the initial penetration of the BR-350B (capped) round as 84mm at 500m. Of course we do not know whether the capped rounds were available in the engagement in question. But assume it was."

Miles Krogfus' article on Russian penetration figures is now available in the May-Aug. issue of AFV News, and is a "must have" for armor penetration fiends.

According to Miles, Russian penetration data for 76.2mm BR-350B ammo is against high hardness armor, which I believe to be face-hardened, and is further reduced in general applicability by one other fact that Miles brings out in his article.

The article states that the Russians produced two qualities of 76.2mm APBC ammo, the general type being mass produced in quantity and a special high potency round which was available but in smaller lots.

The published penetration data on the Russian Battlefield site agrees fairly well with the predicted performance of the high potency Russian 76.2mm APBC, and would not apply to the typical ammo used by that gun.

One cannot apply Russian Battlefield penetration figures directly to Tiger armor cause the estimates are against an entirely different type of armor.

Starting from U.S. tests with 122mm APBC and working to an estimate for BR-350B average ammo at 500m with 662 m/s muzzle velocity, we obtained 72mm penetration at 500m against homogeneous armor plate. And 77mm penetration at 250m.

So at 500m it is doubtful that T34/76 typical BR-350B will defeat Tiger side armor.

The souped up BR-350B can penetrate Tiger side armor at 500m with a lucky roll and little side angle.

Miles' article indicates that Russian tests against Tiger showed that 76.2mm penetrations could not be obtained at reasonable ranges. However, based on my calculations, penetration estimates for the relatively rare 76.2mm solid shot AP indicate that that round could defeat 82mm at a good range.

Get Miles' article and it will shed some real light on what those figures mean. There is alot more in the article than has been touched on here.

[ April 21, 2003, 06:32 PM: Message edited by: rexford ]

[JasonC]

Why would "high hardness" in Russian tests mean "face hardened"? Surely it is far more likely it means they tested using their own, high brinell steel. On test plate, for instance.

And why start with 122mm, instead of believing a 76mm test? Why use a US test with a different round entirely as the benchmark?

Russian battlefield info differentiates the round, the range, the angle, and initial vs. complete penetration. I've not see comparable detail in any of the alternate claims.

Is your 72mm at 90 degrees? Initial or complete penetration? Why is it 10% lower than CMBB's own numbers?

Also, is the "standard" vs. "high powered" thesis a misunderstanding of the 350A vs. 350B difference, or an actual difference within 350B?

If supposedly the latter, are the Russian test results supposed to be exclusively the high powered select lot? Why would the Russians fool themselves and screw up their own doctrine and tactical practice, by using a round they didn't have in the field?

Then there is the implication, that 76mm would only defeat 70mm front IIIs at 500m, and couldn't penetrate StuGs down to 200m. For which the tactical evidence is what exactly?

As for the statement, couldn't penetrate "at reasonable ranges", that is believable, but I'd expect it to mean something in the 800-1000m range, or at the least 500m, not to mean "no chance beyond 200m and precious little within it".

My analysis was meant to show that even believing the Russian battlefield numbers, you'd still expect 96% protection against shots from random positions within 1 km by Russian 76mm.

I submit the tactical evidence hardly suffices to differentiate 96% from 100% protection. 96% protection even when surrounded and closed with, coupled with complete invunerability with front facing or at long range, would rightly still be seen by the crews as practical invunerability.

The Germans stood off with Tigers, making full use of their superior gun. They did not wade down to point blank if they could help it. CMBB players do, without a qualm.

My judgement on supposed underperformance of the Russian 76mm, 10% below the figures CMBB itself gives, and 6/7ths of what the Russian battlefield site gives for BR-350B initial penetration - and the related claim of total invunerability of Tiger sides - remains a Scottish "not proven". Nothing like what would be needed to establish such a claim has been presented.

[PzKpfw 1]

Originally posted by rexford:

The article states that the Russians produced two qualities of 76.2mm APBC ammo, the general type being mass produced in quantity and a special high potency round which was available but in smaller lots.

Interesting Lorrin, I have seen only an few refrences to this 2nd BR-350B and it was designated an APS round. The BR-350B-APS, it weighed 6.6.kg compared to the BR-350B/AP's 6.5kg, & had a higher MV. I am going to try & find my notes, as I had the MV listed.

Regards, John Waters