George Forty on Panzers vs T34, March 1943

[Kozak]

Originally posted by Kozak:

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

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

But the StuG has dedicated loader and commander, too. The Panzer IV's advantage is a cupola which is higher to start from and has larger vision slits (with covers).

I somehow think that Kozak was comparing Pzkpfw IV to an early model T-34 (commander as gunner). But first-hand experiences, when passed through a middle-hand, can be rather unclear. What StuG's are we talking about, IIIB or IIIG? </font>

[Jeff Duquette]

Paul:

I compared the results of the equations you laid out within this thread with the APG Spaced Armor Report (Nov 1950). The results are of some interest.

A little background; The APG Report details three different test armor plate arrangements. The first arrangement is simply a plate at some obliquity. Like so:

---->/ (slashes being the plate or plates and arrow the projectile)

The second arrangement –spaced armor arrangement A -- was a spaced armor arrangement, with the skirting plate and main armor plate set 16” apart. The plates are parallel to each other and sloped, like so:

---->/ /

The last arrangement –spaced armor arrangement B -- is as above except the plates slope in opposite directions, like so:

---->/ \

Four different projectile types were employed within the tests, to include:

57mm APC M86

57mm AP M70

90mm HVAP M304

90mm APC T50E1

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

57mm APC M86

Comparing your equations with the firing trial results for Armor Arrangement 1:

57mm APC M86 vs. 2” plate at 40-degrees ---->/

Firing Trials Ballistic Limit (BL) = 2149-fps => 2149-fps for t/d of 0.89 for APC vs RHA at 40-degrees actually does equate to 2” worth of protection. Checks out.

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

Armor Arrangement 2: 57mm APC M86 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and are parallel to each other.

---->/ /

Firing Trials Ballistic Limit (BL) = 1943-fps => 1943-fps at 40-degrees equates to an equivalent single plate of about 1.91”. So the firing trials indicate that this particular spaced armor array is actually less efficient than a single 2” plate inclined at 40-deg.

Your equation predicts an equivalent armor thickness of about ~3.39”

Skirt Armor Plate Equivalent = 0.4204”

Main Armor Plate Equivalent = 2.219”

Spaced Armor Modifier = +0.747” (at a striking Velocity of 1943-fps or ~0.592Km/s)

0.4204” + 2.219” + 0.747” = 3.39”

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

Armor Arrangement 3: 57mm APC M86 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and inclined in opposite directions.

---->/ \

Firing Trials Ballistic Limit (BL) = 2755-fps => 2755-fps 40-degrees equates to an equivalent single plate of about 2.86”. So the firing trials indicate that this particular spaced armor array is actually somewhat more efficient than a single 2” + ½” plate inclined at 40-deg.

Your equation predicts an equivalent armor thickness of about ~3.71”

Skirt Armor Plate Equivalent = 0.4204”

Main Armor Plate Equivalent = 2.219”

Spaced Armor Modifier = +1.068” (at a striking Velocity of 2775-fps or ~0.845Km/s)

0.4204” + 2.219” + 1.068” = 3.71”

[rexford]

Originally posted by JasonC:

The reason the in-game StuG is invulnerable even to 85mm seems to be double counted shatter. At that range CMBBs own numbers would have the 85mm punching through more than 100mm. Upper hull hits on StuG, the common hit and the weaker slope, are nearly flat.

Thus my testbed's name - "uberstug"...

I just set up a scenario, 7 T34/85 facing 5 StuG IIIG, June 1944, 85mm gun does not have any tungsten rounds. 650m range over flat unobstructed terrain.

End of first turn, all five StuG III penetrated through frontal armor.

No problem with 85mm APBC, which does not have an armor piercing cap and would be subject to shatter gap to some degree.

Looking at the drawings of StuG IIIG, the driver visor that pokes out from the 30mm/50mm armor protection is probably one of the most vulnerable locations along with the 50mm flat slope mantlet on the gun.

The upper superstructure on the StuG III consists of 30mm at 68 degrees from vertical and 50mm at 51 degrees.

[ November 18, 2003, 10:41 PM: Message edited by: rexford ]

[rexford]

Paul,

The problem as I see with your equation predictions for the case where two face-hardened plates are in contact is just that, I doubt that the basis for your math is firing tests with face-hardened armor.

As described in my earlier posts on this and other threads, homogeneous plates are weakest on the surface, since the armor in those areas is relatively unconstrained by surrounding material and is easiest to push out of the way.

Two homogeneous plates in contact present twice the surface area of a single plate of the same total thickness, therefore two plates in contact are weaker than one plate.

Face-hardened plates, on the other hand, obtain practically all of their resistance from the thin super hard surface layer, and two 30mm face-hardened plates in contact present two face-hardened layers with a total face-hardening that is more than twice as thick as one 60mm plate.

Two face-hardened plates in contact should be better than one, while two homogeneous plates in contact should be less effective than one.

With regard to air spaces, when a plate combination is hit and the round penetrates into the first plate, the bulge at the rear of the outer plate should reach back and touch the inner plate.

So, from a ballistic perspective, two plates in contact with a tiny air space between them will be penetrated like two plates in contact without an air space between them.

I do not buy the equation results since they appear to be based on a different armor type, and the air space theory does not seem reasonable once a round hits and penetrates into the outer plate.

Lorrin

[ November 18, 2003, 10:14 PM: Message edited by: rexford ]

[rexford]

Placing six SU 85 vs 2 StuG IIIG during a December 1943 scenario on clear flat ground, 700m range, resulted in no clean 85mm penetrations that were not at weak points during the first turn.

CMBB appears to correctly model 85mm APBC ammo, and does not do a reasonable job with 85mm AP against 80mm frontal armor, based on the two scenario's I tested.

So, JasonC should bring this up with the CMBB design team but should be specific about the ammo types he is referring to.

Whether it is due to overmodelling of two plates in contact, over zealous application of shatter gap or whatever is open to question.

With regard to shatter gap, the basic theory is that an uncapped, low nose hardness round that strikes at 20 degrees to 45 degrees or so MAY fail to penetrate even though the penetration is 105% to 125% of the armor effective resistance. Hits at less than 20 degrees impact angle may not be vulnerable to shatter gap.

It may be prudent and reasonable to ask how the shatter gap theory is applied in the game to 80mm armor hit by 85mm AP rounds at angles from 0 to 45 degrees.

[Jeff Duquette]

Paul:

The trend is about the same with 57mm AP. The firing trial results against the spaced armor arrays seem to indicate an equivalent single plate being lower than what the equation you have presented would predict. Of particular interest is 57mm AP and APC trials that seemingly show a lower equivalent armor thickness for the parallel plate arrangement…---->/ /.

This trend doesn’t seem to hold true with the 90mm APC round. In all but one case, both the spaced armor arrays …---->/ /…and …---->/ \ were typically resulting in higher BLs than the single plate -->/.

Does the equivalent spaced armor equation you have presented have its origins in long-rod penetrator firing trials?

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

57mm AP M70 Results

Armor Arrangement 1:

57mm AP M70 vs. 2” plate at 40-degrees

---->/

Firing Trials Ballistic Limit (BL) = 1997-fps => 1997-fps for t/d of 0.89 and AP vs RHA at 40-degrees does equate to typical BL for 2” worth of protection. Checks out.

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

Armor Arrangement 2: 57mm AP M70 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and are parallel to each other.

---->/ /

Firing Trials Ballistic Limit (BL) = 1772-fps => 1772-fps at 40-degrees equates to an equivalent single plate of about 1.95”. So the firing trials indicate that this particular spaced armor array is actually less efficient than a single 2” plate inclined at 40-deg.

Your equation predicts an equivalent armor thickness of ~3.32”

Skirt Armor Plate Equivalent = 0.4204”

Main Armor Plate Equivalent = 2.219”

Spaced Armor Modifier = +0.682” (at a striking Velocity of 1772-fps or ~0.5401Km/s)

0.4204” + 2.219” + 0.682” = 3.32”

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

Armor Arrangement 3: 57mm AP M70 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and inclined in opposite directions.

---->/ \

Firing Trials Ballistic Limit (BL) = 2620-fps => 2620-fps at 40-degrees equates to an equivalent single plate of about 2.7”. So the firing trials indicate that this particular spaced armor array is actually somewhat more efficient than a sstraight-up 2” + ½” plates inclined at 40-deg.

Your equation predicts an equivalent armor thickness of ~3.65”

Skirt Armor Plate Equivalent = 0.4204”

Main Armor Plate Equivalent = 2.219”

Spaced Armor Modifier = +1.008” (at a striking Velocity of 2775-fps or ~0.845Km/s)

0.4204” + 2.219” + 1.008” = 3.65”

[ November 18, 2003, 11:04 PM: Message edited by: Jeff Duquette ]

[Redwolf]

[never mind]

[ November 18, 2003, 10:57 PM: Message edited by: redwolf ]

[JasonC]

The upper hull is the more commonly hit and the easier to penetrate, Paul, so it is the "rate determiner". 10 degree slope only. The bow-lower hull has better slope but if the upper hull can be holed the vehicle is vulnerabl,e and that happens sooner, so it determines tactically significant ranges.

Rexford, I don't doubt the 1944 ammo performs better, and lowering the range 150m will also help. I've noticed many times that fall 43 Russian 85s royally stink, making the SU-85 nearly useless in the period when it is out and the T-34/85 isn't.

I also went to the library today to look up GDs tank fleet available in early 43. No dice on the 50L60 theory. They had only 10 Pz III longs left in February, before the refit, as against more than 40 Pz IV longs. After the figures are even worse. There is thus no chance the tactical report is due to 50L60 rather than long 75 penetration range considerations.

If it is any consolation, Jentz does call them "75L43" IV longs. But there is no avoiding the inference, that at least in early 1943 both Germans and Russians thought the T-34 glacis was proof against a German long 75 at ranges over 1250m. See Jentz volume 2, pages 36 and 37 in the German edition (don't know if the pages are the same in English).

It should not be a surprise. The 75L48 also fails over 800m (being generous - some sources I've seen say 600m) against W armor Shermans. Panzerjaegers equipped with Jagd IVs in the south of France report as much in AARs, lamenting not having the newer L70 Jagds to "deal".

It is a good gun but not an 88L56 or 75L70. It made plain vanilla German AFVs - Pz IVs and StuGs - the equals of T-34s and Shermans, with a range edge against the less well gunned early series of both, reversing for the later upgunned Allied varieties. It did not make them ubertanks that outclassed the vanilla Allied types.

[ November 19, 2003, 12:47 AM: Message edited by: JasonC ]

[rexford]

Originally posted by JasonC:

Rexford, I don't doubt the 1944 ammo performs better, and lowering the range 150m will also help. I've noticed many times that fall 43 Russian 85s royally stink, making the SU-85 nearly useless in the period when it is out and the T-34/85 isn't.

I also went to the library today to look up GDs tank fleet available in early 43. No dice on the 50L60 theory. They had only 10 Pz III longs left in February, before the refit, as against more than 40 Pz IV longs. After the figures are even worse. There is thus no chance the tactical report is due to 50L60 rather than long 75 penetration range considerations.

If it is any consolation, Jentz does call them "75L43" IV longs. But there is no avoiding the inference, that at least in early 1943 both Germans and Russians thought the T-34 glacis was proof against a German long 75 at ranges over 1250m. See Jentz volume 2, pages 36 and 37 in the German edition (don't know if the pages are the same in English).

It should not be a surprise. The 75L48 also fails over 800m (being generous - some sources I've seen say 600m) against W armor Shermans. Panzerjaegers equipped with Jagd IVs in the south of France report as much in AARs, lamenting not having the newer L70 Jagds to "deal".

JasonC,

The above notes contain some good stuff, which I would like to comment on a little so we both understand each other a bit better.

A. Your point about 85mm AP being pretty poor against armor it should defeat is very good, and should be brought to the attention of the designers.

If you want help packaging it I'am willing and available, we can do it on this forum or via private e-mails.

B. Very good effort on 75L43 guns in GD use during early 1943, although a source would help. From the March 1943 report T34 knew they could stand off at 1235m and be "safe" against PzKpfw IV's. This suggests that armor resistance for T34's in Kharkov area was well above other T34's, it doesn't suggest that ALL T34 had same quality armor.

Say penetration probability for 75L43 hit on T34 glacis at 1235m is 5%, this means resistance is about 112mm vertical.

So, either the 45mm/60 degree plates have a quality multiplier of 0.92 or maybe the plate thickness is close to 50mm with a quality of 0.80.

From you have presented it does appear that the T34 's at Kharkov in the spring of 1943 were much more resistant than the average T34 that is modeled in CMBB.

C. Tell me what Jentz says on pages 36 and 37 in Vol. 2, I sold my copy long ago.

Jentz also gives 1200m for 75L43 penetration of T34 at any angle, and 1600m max range.

D. The 800m range for 75L48 against 47 degree glacis Shermans comes from where?

The W series Shermans had 2.5" plates at 47 degrees slope, which resists 75mm APCBC hits like 114.4mm vertical effective according to our equations (quality is 1.00 due to improved quality control and heat treatment after 10/43). According to my calculations, 75L48 APCBC penetrates 114.4mm vertical at 807m without a side angle to the shot.

So you see our calculations are in line with the reported range for 75L48 against 47 degree Sherman glacis armor.

The Germans stated in a report that we obtained that 75L48 APCBC could not penetrate the 47 degree Sherman glacis at 1000m.

One other thing, German quality of 75mm APCBC varied widely and so did nose hardness, so one might expect an average penetration range of 800m against 47 degree Sherman glacis armor with a low range of 600m on occasion. One or two AAR's do not a universe make, and one must consider ammo quality (as well as better than average armor).

E. The U.S. analysis of T34/85 45mm plates (from Russian tanks found in Berlin ruins) showed that the armor ranged from poor to excellent quality, and firing tests showed that it resisted with less effectiveness than medium hardness U.S. armor.

German firing tests against T34 like armor (same composition, high hardness and manufacture, with thicknesses in the 42mm to 52mm range) showed the armor to be inferior to medium hardness plate.

My opinion on the March 1943 Kharkov T34 is that they had much more than 45mm thickness on the glacis, but this is speculation.

Lorrin

[ November 19, 2003, 05:32 PM: Message edited by: rexford ]

[rexford]

Ballistic data for effective resistance of sloped rolled plates against 75mm APCBC ammo results in following estimates for quality = 1.00 :

T34 Glacis

45mm/60 degrees resists like 122.3mm vertical

High hardness plate, highly variable quality

W Sherman Glacis

63.5mm/47 degrees resists like 114.4mm verticalMedium hardness plate

Hetzer Glacis

60mm/60 degrees resists like 174.9mm vertical

Panther Glacis

82mm/55 degrees resists like 209.6mm vertical

Variable resistance to cracking and (maybe) penetration

Sherman Glacis

50.8mm/56 degrees resists like 119.1 vertical

Tends to have quality below 1.00 due to inferior quality control, odd chemical compositions, poor heat treatment and multiple pieces which places welds in harms way

[rexford]

When the Germans duplicated T34 armor for early 1942 firing tests with 37mm and 50mm guns, they selected thicknesses from 42.1mm to 53.3mm with near constant hardnesses (around 450 Brinell or so).

The above data suggests that T34 armor plates on hull could have ranged from just under 45mm to well over 45mm, which could account in part for the variable penetration ranges in the reports we have discussed.

Regarding AAR's, a fellow on the Yahoo! Tankers site has a 1945 report from Hungary where Hetzer hits on the T34/85 glacis were failing at 250m range (if my memory serves me). Ammo quality variations could account for alot.

Miles Krogfus has indicated that German 75mm APCBC nose hardness varied from 56 to 69 Rockwell C hardness, which could easily result in an ammo batch penetrating 10% less than average.

On October 12, 2003, Miles posted the following on the Tankers site regarding German 75mm APCBC:

"Sample lots from seven makers showed quality variations that would be equal to a circa 24 % velocity difference worst to best projectiles

to perforate the same thickness of homogeneous armor plate. Four makers of U.S 75 and 76 mm M 61 and 62 projectiles showed a 20% velocity difference. Variation in quality of projectile made more of a difference when a projectile struck a plate than variations in armor plate quality."

If the projectiles have the average halfway from best to worst and follow a bell-shaped curve, we're talking about the worst rounds penetrating -17% less than average and the best penetrating +17% more.

A bad lot could penetrate 10% less than average for some unfortunate group of vehicles.

[rexford]

If Kharkov 1943 T34 had 50mm glacis with 0.79 quality (calculated from our math model), the effective resistance would be 110mm vertical at 1.00 quality.

With 101mm vertical penetration at 1250m, 75L43 APCBC would have a 7% penetration probability in the absence of a side angle. Assumes 5.7% standard deviation for German 75mm ammo quality variations.

If 75L43 APCBC quality was less than average, penetration probability would decrease.

So increasing T34 armor resistance by 19% over what was held to be the average (45mm at 0.76 quality) results in about the right range for 75L43 defeats in the one case under investigation.

However, maybe the 1200m "penetration at any angle" and 1600m "max penetration" by 75L43 were against 42mm poor quality T34 plates using above average 75mm ammo.

Who knows at this point which range is the true average?

Maybe looking at German 50mm gun penetration cases against T34 will shed additional light regarding the real averages to be used for T34 armor.

[ November 19, 2003, 07:26 PM: Message edited by: rexford ]

[Paul Lakowski]

Hi Jeff I have this paper....

Originally posted by Jeff Duquette:

Paul:

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

57mm APC M86

Comparing your equations with the firing trial results for Armor Arrangement 1:

57mm APC M86 vs. 2” plate at 40-degrees ---->/

Firing Trials Ballistic Limit (BL) = 2149-fps => 2149-fps for t/d of 0.89 for APC vs RHA at 40-degrees actually does equate to 2” worth of protection. Checks out.

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

Armor Arrangement 2: 57mm APC M86 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and are parallel to each other.

---->/ /

Firing Trials Ballistic Limit (BL) = 1943-fps => 1943-fps at 40-degrees equates to an equivalent single plate of about 1.91”. So the firing trials indicate that this particular spaced armor array is actually less efficient than a single 2” plate inclined at 40-deg.

Your equation predicts an equivalent armor thickness of about ~3.39”

Skirt Armor Plate Equivalent = 0.4204”

Main Armor Plate Equivalent = 2.219”

Spaced Armor Modifier = +0.747” (at a striking Velocity of 1943-fps or ~0.592Km/s)

0.4204” + 2.219” + 0.747” = 3.39”

OK the skirting plate was untreated 1/4 inch plates sandwiched together [doesn't state how].

This could mean mild steel which can be 180BHN [0.8 Te] or down to ~ 100 BHN [~ 0.66]...anything lower would be soft steel.

Since its not stated which steel is used this could be either or and will modify the results.

More importantly is the fact that the researchers identified the 57mm ammo to do better than they thought since it had higher longditudeal properties. Now I'm not sure what they mean't by this but it sounds like high strength [as opposed to high hardness]. Its long been known that high strength penetrators do better than regular strength penetrators in both penetration and multi layered armor penetrations....and spaced armor is no different. THis is why modern APFSDS are moving back to these.

In modern ballistics tests with APFSDS such a high strength penetrators demonstrate a 70% lower spaced plate effect [goes from 1.3d to 0.9d] . If we apply this to the 57mm case the situation improves dramatically.

BTW the body diameters of these rounds look to be 5.75cm M70 and 5.6cm M-86.

Two 1/4 inch mild steel plates and one 2 inch RHA plate workout to [cm sorry I'm sooo European ] 0.635cm x 2 plus 5.08cm. The t/d Vs M-86 works out to 0.56 & 0.91 respectively ..adding Te = 0.37 x 1.27= 0.47cm and 4.61cm.

The spaced plate effect should be SQRT [0.61/5.6] = 0.33d x 0.7 = + 1.3

The angled plate looks to be 7.9cm or about 3.1 inches. This doesn't explain the parrallel plates but looks close to the opposing plates....

Looking over the parrallel plates I recall the yaw and pitch factor that altered the impact on the second plate reducing the angle by up to 7°.That never happens with APFSDS so they never added that factor....guess thats a modification that needs to be added for AP level penetrations.

That should reduce the back plate contribution to 33° or 4.61cm ÷ 0.84= 5.5cm + 1.3+ 0.47cm = 7.3cm or 2.86 inches.

While this may look like a problem it may not be. The M-86 is an APC. Modern research suggest that the cap will truncate the spaced plate effect....and this may be an indication of just how much.If we eliminate the spaced plate effect due to the cap, then the values become 6.6cm [2.6"] and 6cm[2.36"] respectively .

It also should be noted that with spaced plate their seems to be a higher scatter on results than normal AP shots with SD being as high as 10%.

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

Armor Arrangement 3: 57mm APC M86 vs. ½” Skirt Armor 16-inches away from a 2” main plate. Both plates are sloped at 40-degrees and inclined in opposite directions.

---->/ \

Firing Trials Ballistic Limit (BL) = 2755-fps => 2755-fps 40-degrees equates to an equivalent single plate of about 2.86”. So the firing trials indicate that this particular spaced armor array is actually somewhat more efficient than a single 2” + ½” plate inclined at 40-deg.

Your equation predicts an equivalent armor thickness of about ~3.71”

Skirt Armor Plate Equivalent = 0.4204”

Main Armor Plate Equivalent = 2.219”

Spaced Armor Modifier = +1.068” (at a striking Velocity of 2775-fps or ~0.845Km/s)

0.4204” + 2.219” + 1.068” = 3.71”

I must be gettin old cause I Fu#$ something else!!!

The spaced plate effect is not modified by V, just t/d...its the back plate effect to determine penetration in the first place , thats modified by V..... big sorry for that

[A.E.B]

Hi all

An idea has occurred to me - what is the possible effect of corrosion on armour thickness?

Basically, given the right conditions (liquid water and temperature - each 10 degrees Celsius doubles the rate), oxygen will react and convert iron into iron oxide. Normally, a crust of iron oxide (rust) prevents further corrosion unless vibration or abrasion removes the rust.

Of course tanks are made of steel, but they are still subject to rust. Most tanks are given a coating of paint - although some Russian tanks were driven into combat without paint - but battlefield conditions would results in sufficient paint being removed to allow rust to occur. The same battlefield conditions would also tend to remove any rust that forms.

What is means is that poorly maintained tanks (or tanks that were never painted) could easily lose a millimetre or more of steel thickness a week. And this steel would be lost at the surface, which is particularly detrimental to face-hardened armour.

Armour where two plates are directly joined together will be vulnerable if water penetrates the joint and causes rusting as such an area cannot be repainted. Spaced armour if not well ventilated or drained would also provide excellent conditions for rust.

Does anyone know how good German and Russian rust prevention was during WWII?

So a badly maintained T34 going into battle months after it was manufactured could have armour that is considerably thinned by rust.

Regards

A.E.B

[ November 20, 2003, 12:22 AM: Message edited by: A.E.B ]

[Jeff Duquette]

I’m not sure I get it. You are now saying the velocity component is not included in the spaced effect modifier?

So the spaced effect, or spaced modifier is not:

(t/d)^0.5 x 0.1d x V{in Km/s} x gap modifier

???

[Paul Lakowski]

Originally posted by Jeff Duquette:

I’m not sure I get it. You are now saying the velocity component is not included in the spaced effect modifier?

So the spaced effect, or spaced modifier is not:

(t/d)^0.5 x 0.1d x V{in Km/s} x gap modifier

???

It should just be Spaced plate erosion by determine the t/d ; angle & effectiveness of the plate material .

Then (t/d)^0.5 to determine the 'spaced plate effect'

So 2cm Aluminum [0.5d] vs 3cm API becomes

2/3÷2^2=0.8 x 2= 1.6

1.6 x 0.5[te]= 0.8cm

The spaced plate effect becomes

0.8/3^0.5 = 0.5cm

If there is insufficent gap, multiply 'spaced plate effect'by x 0.7.

If the penetrator is high strength reduce the 'spaced plate effect' by x 0.7

So if the penetrator was high strength and the gap insufficent it should be x 0.5.

[Grisha]

Sorry for the offtopic post, but, Jeff Duquette, is your normal email address (not hotmail, the other one) down? I keep getting mail delivery failures.

[Jeff Duquette]

Paul Said So 2cm Aluminum [0.5d] vs 3cm API becomes 2/3÷2^2=0.8 x 2= 1.6

Is that supposed to be (2/3/2)^0.2

[Jeff Duquette]

Originally posted by Grisha:

Sorry for the offtopic post, but, Jeff Duquette, is your normal email address (not hotmail, the other one) down? I keep getting mail delivery failures.

Greg:

I have actually been out of town for work for the last week. Down on the Oregon coast -- east of bum-fu#%ed Egypt -- working on a revetment wall. I am accessing the net via a painfully slow phone modem. My regular home email my be overflowing. I should be home tommorrow and will clear everything out.

[Andreas]

Originally posted by rexford:

C. Tell me what Jentz says on pages 36 and 37 in Vol. 2, I sold my copy long ago.

From Jentz:

1. In the period from 7 March to 20 March 1943, 250 T34, 16 T60 or T70 and 3 KW-1 tanks were knocked out.

2. The number of kills scored by each type of weapon were:

</font>

• 188 by Pz.Kpfw.IV 7,5cm lang</font>
• 41 by Sturmgeschuetz 7,5cm lang</font>
• 30 by Pz.Kpfw.VI (Tiger)</font>
• 4 by 7,5cm Pak (mot Zug)</font>
• 4 by 7,5cm Pak (Sfl)</font>
• 1 by a direct hit from a sIG</font>
• 1 using a Hafthohlladung</font>

(PR GD began with 5 Pz II, 20 Pz III 50L60, 10 Pz IV 75L24, 75 Pz IV 75L43, 9 Pz VI 88L56, 2 PzBefWg 50L42, and 26 Flammpanzer III. Their losses and total write offs amounted to 1 Pz III 50L60, 1 Pz IV 75L24, 11 Pz IV 75L43 and 1 Pz VI Tiger).

3. Degradation of the Russian armour steel was not noticeable. However, the armor steel is darker and finished rougher. The tanks reveal they were produced in a short time, because there is no evidence of any close tolerance work. The turret of the T34 is not made form a single piece,; instead it is assembled from numerous pieces. In many T34 tanks the armor walls wre created from pieces of 1cm thick steel with 6cm filling of cast iron or other material and then a second piece of 1cm thick steel.

I take it that is what you are after?

As for in-game experiences, I have just had a SU-85 in June 44 (non Tungsten) fire three times at >80m frontally at a Stug. Three times partial penetration only. Is that shatter gap at work?

Stug died nevertheless.

[c3k]

Gents,

Regarding T-34 glacis resistance computations. It's all well and good to consider the slope, thickness, etc., but let's keep this in perspective. The glacis was the front of the tank. In the middle of the glacis was a big hole. The Soviets made 'em like that. It was the driver's hatch. Okay, since this is my main point, I'll repeat it: in the middle of the glacis is a big hole.

The glacis was not some infinite-sized, flawless field. Let's delve more deeply, shall we?

The hole represents a certain, definable, area of the entire glacis. I recall an earlier poster saying 14%. (Relying on memory. If anyone has an accurate drawing, it should be a simple exercise to determine the real area.)

This brings up two zones of, I assume, greatly weakened glacis resistance. The glacis area near the edge of the hole will resist with a lesser ability than other glacis areas. This is the "edge effect" noted by Rexford. How far from the edge does the "edge effect" zone go? What is it's resistance? I assume some sort of gradation from near 99% theoretical maximum resistance to, as you approach the edge, a drop off to 0% resistance as you enter the edge. This _increases_ the area of weakness of the glacis.

The other zone of non-glacis resistance is, of course, the actual driver's hatch. Does anyone have any figures for thickness? BHN? Edge effects? How does the hinge arrangement modify resistance? Et cetera.

Given an assumed weak zone centered on the driver's hatch, what percentage of German shots, aimed at center of mass of the glacis, will disperse towards, and impact upon this weak zone?

What is the total area of the weak zone? What is the total area of the _likely to be hit zone_ which is weak?

These are non-trivial aspects. The problem here is NOT how the T-34 glacis resists penetration, but WHAT IS A SAFE RANGE FOR A T-34 TO BE FROM A GERMAN TANK. Obviously, glacis resistance is a, if not the, major determinant.

Again, in good military taught manner, I'll repeat my main point: IN THE MIDDLE OF THE T-34 GLACIS IS A BIG HOLE. HOW THIS HOLE RESISTS IS SOMEWHAT IMPORTANT TO THE SURVIVAL OF THE T-34.

Thanks,

Ken

[JasonC]

On the rust idea, it won't be a significant issue. First it is only going to happen where paint is lost, second it will only go down a tiny distant. But above all, T-34s just didn't live long enough for it to have time to accumulate. The turnover time for T-34s was about a year, with losses and new production each about equal to the size of the whole fleet in that time. Including those in the depots, being repaired, being deployed, etc. 3 months, sure, tanks might be around for that long. But these aren't 1942 survivors in 1945.

On the idea that the T-34s in the Kharkov area were something special or a quarter inch thicker, it is an absurd inference with absolutely nothing to back it. Note this wasn't a side area but the main front in the war at the time. The Russian units that fought there came from the later portions of the winter offensive, and reserves added to that drive later. The Germans had no trouble giving them a thorough operational drubbing from February to the end of March.

The obvious explanation is simply that 75L43 doesn't penetrate T-34s as far as some people thought. That is, incidentally, compatible with somewhat higher range figures for 75L48, which is a marginally better gun than the earlier L43. The obvious place in Rexford's numbers is the 0.76 quality rating, which seems absurdly low on its face - there should be no surprise at all in .85 - if not higher still - being more accurate.

Yes that means lower kill ranges - the whole point of the thread is that the AARs from the actual participants are saying those would be correct. Instead of spinning that away, why not take it seriously? What is the supposed evidence for 0.75 - trials with somebody else's steel thought to be similar, instead of the real thing? Tests against entirely different guns at entirely different ranges? As for the 1600m figure, it doesn't say hull front so it is quite a stretch to pretend it must mean hull front. It would fit for the turret front with penetration at more like 1200m for the hull.

Other evidence that German 75s had middling ranges - in a book on StuGs I found a discussion fo tactics and ranges that mentions the danger from SU-152s, which included the point that they like to stand off at 1500m, because the German gun won't reliably kill them at that range while their reply will. The SU-152 has only 75mm at 30 degrees - akin to the T-34 turret front, which is 70mm curved.

If you look at CMBB numbers for L43 and L48 at 1500 vs. 30, they give 73.5 and 75 on a linear interpolation between 1000 and 2000. They will not fail against the SU-152 in CMBB because the latter is rated only 0.9 armor quality. German training documents and Russian range practices evidently did not recognize this supposedly low quality of the Russian armor.

There is every indication the German 75mm numbers are somewhat generous (particularly for the L43, only 2mm below the L48 typically), and the Russian armor quality numbers low-balled when the AARs don't show it.

Rexford speculates that German ammo "unevenness" may also be involved. Perhaps, but that is modeled by shot to shot variation. If the ammo regularly performs up to 20% worse, then the center of the distribution of "rolls" for each shot should be .9 of max, not max. Notice, you effective get the same result by not lowballing the armor quality opposite. If you assume perfect ammo penetration numbers and lowball armor quality on the other end, however, you will erroneously throw out all the poor rounds and keep all the best ones. It is like comparing the top of one distribution to the bottom of another, which will predictably give ahistorical outcomes.

The tactical reality is the Germans did not treat the 75 as an "any range" T-34 killer but as a "km range T-34 killer" - and used it quite successfully that way, I might add. The Tiger was different in that it could and did regularly kill T-34s out to 2 km.

Incidentally, I notice one other passage in Jentz talking about kills scored by various German weapons, including 50L60 after long 75s were out. It speaks of 150m ranges, side shots, and Pz Gr 40 (the last vs. a KV-1). Not we stood off at 800m and put one through the turret front. Before the Germans had long 75s in numbers, T-34s were considered very tough. People tend to forget they were only about 40% of the 1942 fleet, which was the smallest overall AFV fleet the Russian ever had.

As for the Jagd AAR, it was the Panzerjaeger battalion of the 11th Panzer division fighting in the withdrawal from southern France. They had to fight through the Americans at Montelimar to free what they could of the army in the south. The Jagds had trouble, while Panthers succeeded.

[Panzer76]

This might be of interest to you, seems BFC changed the penetration algorithm, or somfink:

http://www.battlefront.com/cgi-bin/bbs/ultimatebb.cgi?ubb=get_topic;f=30;t=000267

[Paul Lakowski]

Originally posted by Jeff Duquette:

Paul Said So 2cm Aluminum [0.5d] vs 3cm API becomes 2/3÷2^2=0.8 x 2= 1.6

Is that supposed to be (2/3/2)^0.2

2cm/3cm ÷ 2^0.2 ....yes thats right.

[rexford]

Originally posted by JasonC:

"On the idea that the T-34s in the Kharkov area were something special or a quarter inch thicker, it is an absurd inference with absolutely nothing to back it."

5m is one-fifth of an inch (50mm vs 45mm), and it is not an absurd inference but a possible explanation, one of many possibilities. And it is not absurd, since the Germans modeled T34 armor with plates ranging from 42mm to 53mm thickness.

Perhaps you just like to discount possibilities out of hand because they conflict with your ideas.

"The obvious explanation is simply that 75L43 doesn't penetrate T-34s as far as some people thought."

No, the obvious explanation is that T34 armor resistance seems to vary much more than other tanks, which is not unexpected given the stresses on Russian industry at the time.

"The obvious place in Rexford's numbers is the 0.76 quality rating, which seems absurdly low on its face - there should be no surprise at all in .85 - if not higher still - being more accurate."

Tell me why it seems absurdly low. What research have you seen for 45mm high hardness plates attacked by 75mm APCBC which suggests something higher is more plausible?

"Yes that means lower kill ranges - the whole point of the thread is that the AARs from the actual participants are saying those would be correct."

And the whole point of the thread is to show that there is conflicting into here, some suggests lower ranges and some suggests higher.

"Instead of spinning that away, why not take it seriously? What is the supposed evidence for 0.75 - trials with somebody else's steel thought to be similar, instead of the real thing? Tests against entirely different guns at entirely different ranges?"

U.S. ammo against U.S. high hardness armor results in about the same conclusions as German ammo against German reproduction of T34 armor. U.S. ammo against captured T34/85 armor shows that armor is much less resistant than medium hardness U.S. armor.

"As for the 1600m figure, it doesn't say hull front so it is quite a stretch to pretend it must mean hull front."

As I have stated so many times before, T34 were attacking German positions and front penetrations would be critical factor.

"Other evidence that German 75s had middling ranges - in a book on StuGs I found a discussion fo tactics and ranges that mentions the danger from SU-152s, which included the point that they like to stand off at 1500m, because the German gun won't reliably kill them at that range while their reply will. The SU-152 has only 75mm at 30 degrees - akin to the T-34 turret front, which is 70mm curved."

Your evidence is easily explained away, as usual. 75mm at 30 degrees resists 75mm APCBC like 92mm vertical, 75mmL48 penetration at 1500m is 97mm so given a slight side angle and random variations in projectile quality, 75mm L48 APCBC won't penetrate on every hit against 75mm/30 degrees.

Regarding your comparison with T34 turret front, 1235m is stated "safe" range and most of T34 turret front is not a flat 70mm/30 degrees but highly sloped gun sponson areas, with a big flat mantlet in front.

"If you look at CMBB numbers for L43 and L48 at 1500 vs. 30, they give 73.5 and 75 on a linear interpolation between 1000 and 2000. They will not fail against the SU-152 in CMBB because the latter is rated only 0.9 armor quality. German training documents and Russian range practices evidently did not recognize this supposedly low quality of the Russian armor."

Why don't you package all of this with the proper references and bring it up with the designers. Some of what you say has merit and would make a very good case for change.

"There is every indication the German 75mm numbers are somewhat generous (particularly for the L43, only 2mm below the L48 typically), and the Russian armor quality numbers low-balled when the AARs don't show it."

The 75mm L43 fired APCBC at 740 m/s, the 75mm L48 at 750 m/s. That relates to an expected 1.9% difference in penetration. To say that a 2mm difference in penetration is "generous" shows that you didn't do enough homework to make a very good case.

"Rexford speculates that German ammo "unevenness" may also be involved. Perhaps, but that is modeled by shot to shot variation."

No it isn't if we are talking about a shipment of rounds from a specific maker that is appreciably below the average.

"The tactical reality is the Germans did not treat the 75 as an "any range" T-34 killer but as a "km range T-34 killer" - and used it quite successfully that way, I might add."

The above statement really says nothing, no one ever said that the 75mm L43 was an "any range" T34 killer.

I offered to help you put together a package for submittal to the CMBB designers, complete with references and sources. Your response suggests that you wish to continue the same old arguments on this forum.

[ November 20, 2003, 07:54 PM: Message edited by: rexford ]