Two Plates In Contact

[rexford]

Paul Lakowski recently provided this writer with a copy of A. Hurlich's paper on SPACED ARMOR, which was published on November 20, 1950 by Watertown Arsenal in the U.S.

The paper starts with a discussion of two plates in contact and presents data from a test at 45 degrees impact, where two 1.5" homogeneous armor plates were equivalent to a single plate with 2.3" thickness.

The inferiority of two 1.5" plates to a single 3" plate was related to the ease with which material on or near the surface of plates can be moved. Two 1.5" plates in contact have considerably more surface area than a single 3" plate, leading to less penetration resistance.

If the test results from the Hurlich paper are combined with two results from U.S. Navy tests, a broader view of what occurs when two layered plates are attacked might be obtained:

1.5" over 1.5" resists like 76.0% of combined thickness

3.0" over 1.0" resists like 92.5% of combined thickness

1.0" over 3.0" resists like 87.5% of combined thickness

The above data suggests that thicker plates result in the retention of a high percentage of the combined thickness as effective armor (greater ratio of middle area to surface material), and placing a thinner plate in back of the thicker armor increases the resistance.

The following equation reproduces the above results (where effectiveness is multiplier on combined thickness that resists penetration when two plates are in contact):

Effectiveness = 0.3128 x (plate ratio)^0.02527 x (maximum thickness)^0.2439

where,

"plate ratio" is thickness of first plate to be hit divided by underlying thickness

"maximum thickness" is thickness in millimeters of thickest plate

When two 100mm plates are in contact, the above equation predicts an effectiveness of .96, suggesting that two 100mm plates would resist like a single 192mm thickness. Effectiveness over 1.00 is not possible, and a limit on how large the factor can be probably exists.

Due to the limited data base the equation is preliminary, and additional test data and suggestions would be appreciated.

-----------------------------------------

Sherman tanks carried applique armor on the hull side, adding 25mm on early versions and 38mm on later models to protect the ammo racks.

Using the above equation, 25mm/38mm on early Sherman hull sides would resist penetration like

0.75 x 63mm, or 47mm, and 38mm/38mm would be equivalent to a single plate thickness of 58mm.

The 89mm+89mm Sherman Jumbo cast mantlet would resist like a single casting of 166mm thickness, which would be the same as 166mm of rolled armor.

The Sherman Jumbo glacis, 38mm over 63.5mm, would resist like a single rolled plate with 86mm thickness. The resistance against 75mm and 88mm APCBC, corrected for slope effect, would be about 172mm and 163mm of vertical rolled plate.

Panther and Tiger II hits on the Sherman mantlet and glacis might be expected to penetrate at:

Panther

penetrate mantlet at 550m

penetrate glacis at 400m

Tiger II

penetrate mantlet at 2100m

penetrate glacis at 2600m

Since the math model is preliminary, it would be interesting to see if any combat reports confirm or contradict the above estimates.

[RenoFlame 36]

It's always interested me what a difference it makes if the projectile strikes the armor surface straight on, or at an angle.

Even the Tiger I's were supposed to present a "corner" to the enemy in order to take advantage of the angle.

[Redwolf]

<blockquote>quote:</font><hr>Originally posted by RenoFlame 36:

It's always interested me what a difference it makes if the projectile strikes the armor surface straight on, or at an angle.

Even the Tiger I's were supposed to present a "corner" to the enemy in order to take advantage of the angle.<hr></blockquote>

Actually, it is rather only heavy tanks like the Tiger I which do this, because it requires that the side armor is in the same thickness ballpark than the front armor. This is also less useful when the vehicle front is angled to start from and it may even be counterproductive when the turret's side at angled to make the turret front narrow, like on the Tiger II. If you would approach in a 35 or 40 degrees angle towards an AT position, you would make the forward turret side more, not less vulnerable.

[TSword]

Another proof how wrong CMBO is...., thx to rexford he corrects things step by step.

The sad thing is, i think we will have to go over the same thing again with CMBB.

[Moon]

What makes you think so, TSword?

[rune]

Moon,

Thought you knew better then to feed the trolls. Look at the logic here, CMBO got it wrong and it took 1.5 years after the game was released, a study well hidden that even rexford didn't have, and rexford admits it is a theory and not fact. [but a good theory in my book] From that we leap into CMBB. If that isn't trolling, then what is?

Rune

[ 12-27-2001: Message edited by: rune ]</p>

[Mattias]

[ 12-27-2001: Message edited by: Mattias ]</p>

[Hanns]

Great post Rexford! I'm assuming that a thin rear plate would also stop or minimize spalling from cast armor. Would this be correct? Also not sure if you caught the thread on the Tiger I restoration. It's got some great pics of the total tear down and rebuild. I'd be interested to know if when they tore it down to it's base components if anyone did some detailed measurements on such things as the turret and glacis thickness. Not sure a museum would be interested in stuff like this but the info would be invaluable for gaming purposes. A last question. How were the larger cast pieces of armor heat treated? Were they air cooled or quenched? Also does anyone know if a non-destructive test (such as ultrasound) would be able to determine if the plate was flawed or impoperly hardened? Would a flawed plate have a different resonance? I can just see an armor grog at a tank museum trying to explain to the guards why he was up on a KT turret with a baby ultrasound scanner For those that missed the link to the Tiger 131 rebuild

Tiger 131 resto

Hanns

[ 12-27-2001: Message edited by: Hanns ]</p>

[rexford]

Thanks for really great responses.

The U.S. did armor flaw testing with a supersonic gizmo that bounced a wave and then tested to see if the wave was distorted by bad things in the armor. From the reflection they could also estimate the size of the flaw. I don't think the device would fit in one's pocket or airport luggage.

The U.S. measured the plates on three Tigers and found that the actual thicknesses exceeded the design spec:

80mm plates were 81.5mm on average

60mm plates were 62.3mm

100mm plates were 103.7mm

The Americans measured the 60mm nose armor on a Panther and it was 67mm.

The 45mm plates on an SU 100 nose actually measured from 42mm to 60mm thickness.

It would have been good if the actual thickness of the tank armor had been measured as it was taken apart and put back together.

About the resistance of two plates in contact, there is very little on the subject and trying to make an equation from three tests is really stretching it. The equation predicts that when 15mm is put on top of 45mm the combination resists like a single 46mm plate: that top 15mm only adds 1mm to the effective resistance?

To make the equation work requires alot of fudge factors, like making 15mm on top of 45mm resist like maybe 50mm (top plate adds at least 0.33 of thickness).

I could see where a game designer might be suspicious of using an equation that has to deal with situations outside the data base where one applies "made up" multipliers. CMBO played it conservative, two plates together act like one plate with same overall thickness. The war was not won or lost based on whether the Sherman Jumbo resisted with 100% of total thickness or 96%, although it might impact a few scenario's.

[Vanir Ausf B]

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

CMBO played it conservative, two plates together act like one plate with same overall thickness.<hr></blockquote>

Actually, Charles did adjust the Jumbo armor thickness down somewhat in the last patch because of this, but as you say, it's probably debatable how correct the current numbers are (hint: TSword).

[Slapdragon]

First, lets ignore TSword. A short look at his extensive posting history (5 posts) show he has one axe to grind: That BTS somehow screwed everything up. Since he is probably a cipher for a banned or current member, there is no real need to pay any attention to him other than to wish him over to the WW2Online forum.

Second, I have an interesting study of ballistic plates in body armor that presents a tested theory that layered plates actually resist steel shot penetration better than a single plate because shock force (one of the several forces at work in penetration) spreads out with each successive plate, spreading out the shock wave that high velocity rounds cause which weaken armor and cause easier penetration.

On the other hand, the use of eratz armor like sandbags rarely have any effect on penetration, making me suspect the situation is far more complex than meets the eye.

None of this is saying that the test Rexford uncovered is wrong, just food for thought. I am curious about what controls where present in the test.

[YankeeDog]

I am not generally scientific or grogic enough to contribute much to a discussion like this, but I have a little tidbit from a seemingly unrelated field that may lend some support to the idea that two plates resist less strongly than one homogenous plate of the same thickness.

I am, among other things, a martial artist. I don't do it much anymore, but I used to do a lot of board/brick breaking for demonstrations and tournaments and such. When one is penetrating wood or masonry with one's fist, two (or more) of a given total thickness are A LOT easier to break than one board of the same thickness. This effect is further magnified if there is a small air space between the boards. For demonstrations, some martial artists place pennies between the boards/bricks to create this air space (known as "pennying" your break). If you do this, breaking a large stack of 12 or more boards/bricks is only slightly harder than breaking one - you just have to make sure you follow through well.

As it turns out, some eggheads at MIT did some research into this phenomenon. They had a martial artist break a "pennyed" stack of boards in front of a super high speed camera. The footage is really interesting. When the fist contacts the first board, it begins to bow, and eventually breaks explosively downward. At this point it actually moves ahead of and breaks contact with the fist, which is still travelling downward. As the fragments of the first board hit the second board it bows and breaks before the fist ever comes into contact with it!! The boards continue to fracture well in front of the fist all the way down the stack.

I have no idea what the physics of this is, but to my eye it appears that the tensile stress (stored elastic potential energy??) in the top layer created by the projectile is released explosively when it ruptures down into the next layer (release of elastic potential energy as kinetic energy??), meaning that some of the projectile's energy is effectively returned to it to help penetrate the next layer.

Of course, steel behaves very differently than wood or masonry, so this is probably all irrelevant. I guess going out and punching a couple of tanks wouldn't prove much, either.

Basically, I'm on my computer for the first time in a week, and looking for an excuse to post.

Interesting discussion - please carry on.

[Amidst Void]

YankeeDog, good post. I would imagine that there are two pennies on each side of the brick (1 penny in the center doesn't contradict my theory however).

Logically, the reason I would say that it's easier to break a stack of 5 bricks with pennies, than 1 whole brick equal to the volume of the 5 bricks, is because one is actually breaking 1 brick at a time with the pennies in between. The penney, creating a small but relevant gap, is quite an aid. Essentially, the martial artist doesn't have to deal with the whole at once, but only parts of the whole, whereas the martial artist facing 1 whole brick (equal to the five) would be facing the whole all at once, making it extremely more difficult. A teenager one day might be able to break all 5 bricks, but on another day he doesn't even come close to breaking a whole brick equal to the 5.

As for tank plates, I don't know how relevant this is. I imagine that tank plates are put extremely tight together, minimazing any gap, but it's possible my theory still works to a lesser extent.

I hope that makes sense.

[ 12-30-2001: Message edited by: Amidst Void ]</p>

[Gyrene]

<blockquote>quote:</font><hr> Also does anyone know if a non-destructive test (such as ultrasound) would be able to determine if the plate was flawed or impoperly hardened? Would a flawed plate have a different resonance? <hr></blockquote>

Yes and no... Ultrasound is used for both Thickness Gaging and for finding flaws, like cracks and casting porosity, but a conventional hardness test is a more accurate indicator.

Eddy Current could also be used to test for close to surface flaws, and X-Ray methods can also be used. All of these methods are possible with very portable machines these days. (Briefcase sized)

Gyrene

[rexford]

In response to the posts on layered armor resistance to AP rounds when the plates are in contact, Nathan Okun e-mailed this writer regarding naval rule of thumb on the subject. Mr. Okun also noted that the equation he uses is

consistent with the naval guideline.

Naval rule of thumb is that when two plates are in contact, the equivalent single plate resistance equals about 70% of the thinner plate thickness plus the thicker plate.

Mr. Okun has found that a "split the difference" approach works well, where the resistance of two plates in contact is taken as the average of the combined thickness and the resistance if the plates were spaced and did not directly interact.

The equation he uses for single plate equivalence is:

((T1 + T2) + (T1^1.4 + T2^1.4)^(1/1.4))/2

The above equation will be referred to as the "working equation" in the comparisons

at the end of this post.

The results from the two abovementioned approaches were compared with the "three points" regression equation developed by this writer. When the maximum plate thickness is at least 2" and the minimum is 1" or greater, the three

equations are fairly consistent in their predictions (less than a 10% variation

between highest and lowest estimates).

The following cases point out some of the larger variations between the three approaches:

1.5" over 1.5" (Sherman side hull with 38mm applique)

Naval rule of thumb: 2.55" single plate equivalence

working equation: 2.73"

three points regression: 2.28"

1.0" over 1.5" (Sherman side hull with 25mm applique)

Naval rule: 2.20"

working equation: 2.28"

three points regression: 1.88"

0.6" over 1.77" (T34 glacis with 15mm applique)

Naval rule: 2.19"

working equation: 2.21"

three points regression: 1.95"

0.8" over 1.77" (T34 glacis with 20mm applique)

Naval rule: 2.33"

working equation: 2.37"

three points regression: 2.01"

89mm over 89mm (Sherman Jumbo gun shield, no modifiers applied for cast armor

deficiency to rolled plate)

Naval rule: 151mm

working equation: 146mm

three points equation: 166mm

38mm over 64mm (Sherman Jumbo glacis)

Naval rule: 91mm

working equation: 85mm

three points regression: 87mm

The difference between the three approaches is due to the inclusion of a 90mm M82 projectile test in the three points regression, where two 1.5" plates in contact resisted as if they were a single 2.28" plate. The Naval rule predicts 2.55" and the working equation estimates 2.46". That point resulted in the equation depressing the overall resistance as the maximum plate thickness decreased below 2".

[ 01-08-2002: Message edited by: rexford ]</p>

[M Hofbauer]

Rexford,

in the original post in this thread, did the test you are referring to take into account the face-hardening of *armor* as opposed to regular homogenous steel plates? *armor* is especially tough on the surface due to the treatment the surface area gets - this effect does not work inside the armor plate. I don't know if you have personally worked with metal before, but remember when you saw/cut through face-hardened steel, it is very tough on the surface but once you get beneath that it is **much** softer?

Therefore, could it be that your statement

The inferiority of two 1.5" plates to a single 3" plate was related to the ease with which material on or near the surface of plates can be moved. Two 1.5" plates in contact have considerably more surface area than a single 3" plate, leading to less penetration resistance.

and the conclusion that massive material is superior than same thickness in layers should be toned down for *armor*, for the reasons that the thicker the armor the harder it is to create it without faults in the first place and the fact that in layered armor the face hardening factor is multiplied ?

I might be way off, those are just some thoughts, curious to hear what you think.

[ 01-08-2002: Message edited by: M Hofbauer ]</p>

[JasonC]

I think the naval equation is more plausible than the one induced from the regression analysis. The latter seems "fudgy" and doesn't make much physical sense, if you look at the funny powers and coefficients. The first thing I'd try would be something like -

thickest times square root of (thick + thin / thick)

With the intuitive idea that the second plate is contributing less resistence than the thicker one, in some smooth falling off fashion. The effectiveness of something tiny like 1mm on a second plate, and most in one plate, should be nearly the same as the one thick plate. This should be true for both "endpoints". The effectiveness of two plates of the same thickness should be a global minimum for "efficiency", in the sense of resistence divided by total thickness. Together, that "derviative analysis" should give the basic shape of the curve.

Square root is simply the most obvious first thing to try after deciding the second plate isn't just as effective as the first (which would be linear, first order, same as the term for the thicker plate, obviously). When you see a first order model isn't accurate enough in physics, you try a second order and see how close that'll get you.

As for the observation that which plate is first, the thicker or the thinner, matters, it may. Which would result in slightly different shapes for the two halves of the curve (up to the plates equal in thickness and back down again). But I also notice that the observations behind this idea are quite limited - both values for the 1 + 3 or 3 + 1 are about .9 x combined thickness, plus or minus less than 3%. It is not obvious from just a couple of tests that that 3% variation is significant rather than random noise. It may be - I am just pointing out that it is hardly established, just from 2 data points.

What would my naive first guess give? Probably less accuracy than the more empirical and detailed navy formula, certainly. But roughly, two plates 1.5 inches thick each gives -

1.5 thickest x 2^.5 = 2.12

Which is 70.7% of the combined thickness, and may well be low. The next "power law" you'd try would be 2/3rds power, and would give 2.55.

What about 3+1? 1/2 power would give 1.33^.5 times the thick plate (3), thus 3.46 or .865 times combined thickness. Reasonably close to the observations but on the low side again. The 2/3rds power approximation would give 1.33^.67 or 3.634, or .9086 times the combined thickness. Much closer.

Just from those numerical examples, I'd suggest a simple model of -

thick x ( (thick+thin)/thick ) ^ 2/3

Notice what happens as thin goes to zero. The right goes to 1^2/3 = 1 and the effectiveness goes to that of the thick plate. Then notice what happens as thin goes to equal to thick (as divided as the overall thickness can be). Then the term on the right goes to 2 ^ 2/3 = 1.587, times thick which in that case is half the overall amount, giving .7937 times the combined thickness, or 2.38 for 1.5" + 1.5".

Corrections to that for which side the thicker plate is on are going to be of a lower order still. For exactness, it would be nice to have that tested and so have more exact shapes of both side of the curve. But the error term from using a simple model like the above is going to be small. A 2/3rds power effect might plausibly arise physically from dimensional considerations (how important area is compared to volume and what-not) - while the powers and coefficients in the regression (from three points) don't suggest anything physically.

A good cross check might be tactical evidence of known penetration facts against historical armors made from layered plates. The most obvious candidates for that are the German Pz III and Pz IV models (and StuGs based on the III), during their uparmoring campaigns.

Thus you often see 30+30 mm armors on the front of midwar tanks. The Germans seem to have consider the protection that afforded equivalent to 1 plate of about 50mm - they replaced 30+30 plates on one model (field modified) to 50mm single plates on subsequent models (factory made). The 2/3rds power formula gives 48mm. They also used 30+50 - the 2/3rds approximation gives 68mm for that combination.

One might look at reported penetration ranges against such models to see if the figures more or less check out. For instance, the Pz III H with 30+30 on the front was used extensively in North Africa, where it faced British 2-pdrs and US 37mm. By the approximation, you'd expect those shells to start failing around 700 yards and fail pretty uniformly beyond 900-1000 yards. While the short 75mm on the Grant or Sherman would remain effective out to 1000-1500 yards.

That fits more or less with the tactical accounts I've seen - the Brits were happy to get Grants because they outranged the Pz IIIs. Of course, it is hard to get anything exact this way, because most plausible approximations of the effectiveness of layered plate will give predications that are quite close in such terms, given the variations involved in tactical (as opposed to test) firing.

Another common case is the 50+30 vs. the Russian 76mm on the T-34. The 2/3rds approximation gave an equivalent thickness of 68mm for that German armor (Pz IV hull fronts, StuG fronts, etc). Against standard BR-350A ammo, that gives an expected penetration range of 500 yards to the T-34 - which is exactly what the Russian accounts say they experienced.

I hope this is useful. An interesting subject.

[rexford]

Regarding the comment about whether face-hardened armor works with the equations presented, I do not believe that it would. You're totally right, with face-hardened armor the surface is what does the damage, so more surface, more damage.

Damn good point!

Here is an explanation posted on another site after I read the above post on CM:

A really good question has been asked about PzKpfw IIIH layered armor and the equations for plates in contact by Nikodemus on the Matrix Games forum.

When the British fired at the 32mm/30mm layered armor on PzKpfw IIIH front hull, they used the 2 and 6 pdrs firing AP, the 37mm firing APCBC, and the Grant/Lee firing AP and APCBC. The resistance of the armor was the same against all rounds, anout 69mm face-hardened.

Why would the two PzKpfw IIIH plates be better than a single 62mm plate, which is not predicted by the naval equation or the regression? Firing test results suggest that 32mm over 30mm, where both are face-hardened, resist like a single 69mm face-hardened plate.

We think it is because the total thickness of face-hardened layers in the 32mm/30mm combo greatly exceeds the layer in a single 62mm plate, and it makes the projectile slam into two very damaging case hardened surfaces.

With homogeneous armor the surface layers are weaker than the middle, so the more surface the less the resistance. Two plates together have much more surface than a single plate with same total thickness.

But with face-hardened armor, the greater the face-hardened surfaces from two plates, the greater the resistance appears to be.

The AP and APCBC rounds in the British test hit the face-hardened layer on the 32mm plate and are damaged but have enough momentum to drive through the softer backing. Then they hit the second face-hardened layer which probably inflicts ALOT more damage on the projectile nose.

Usually with face-hardened armor, once the very hard surface layer is damaged the plate is open to defeat. But with layered armor once the first plate is defeated there is another hard surface staring at the round.

The equations presented in previous posts are for homogeneous armor. Face-hardened armor is another story.

[rexford]

The equation makes sense if one accepts that the thicker the plates the greater the proportion of thickness that would count as interior. So the effective thickness of two 40mm plates in contact and two 110mm plates in contact should be radically different.

40mm/40mm goes to 68mm using the naval rule of thumb, which is 68/80, or 85% of combined thickness.

110mm/110mm goes to 187 using naval guideline, which is 187/220, or 85% of combined thickness.

Since thick plates offer more interior than thin plates (a 15mm plate is mostly surface material in terms of being penetrated), it would seem that a higher percentage of the total combined thickness would resist penetration with thick plates.

[JasonC]

I find the claim that 30+30 resists as 69mm extremely hard to believe. The figure would, however, exactly fit the naval formula for a 30+50 combo, as found on the StuG F and G models and the Pz IV G. Perhaps somebody took a 5 for a 3 somewhere in the chain of this reported result?

There are three reasons I am skeptical of the number, besides the coincidence that it fits for a different armor plate, and that it seems inherently unlikely that two thinner plates outperform one homogeneous one.

One, the Germans did not continue the use of multiple plates, but in every case replaced multiple plates with uniform ones in the next model, after uparmoring a given model with bolted on plates in the field. I find it extremely unlikely they would have done this if in fact the duel plates gave 15% higher protection for the weight, rather than the 15% lower predicted by the naval model.

If they did so once, perhaps it was a failure to learn. But they did not do it just once - it was a uniform practice in multiple model transitions, after field uparmoring of old models with bolted plates.

Two, when they did replace double plates, the thicknesses they chose for the newer model increased the protection rather than decreasing it, as a rule. But they replaced 30+30 plates with single plates 50mm thick, not 70mm thick and upwards.

Three, the 69mm figure for a Pz III H is inherently rather implausible from the known tactical reports. It would suggest the average tank in the DAK was basically invunerable to 2-pdr and 37mm fire from the front, even down to quite low ranges. And that their vunerability to short 75mm was on the order of 1000 yards. But the tactical reports do not show Pz IIIs invunerable to the lighter guns from the front, and the British report that the arrival of short 75s enabled them to outrange everything they faced in DAK armor in mid 1942.

Similarly, that number would put the vunerability of the Pz III H to the T-34 from the front at 500 yards. Which conflicts with tactical reports from 1942, which have the Russians still standing off at 1 km plus. The switch from stand off to close in would happen at the wrong time on the Russian front, by a year.

But if the 69mm number refers to Pz IV Gs with their 30+50mm (and to StuG Fs and Gs, similarly), then it would make perfect sense. The Russian switch happens at the right time. Those later models (some perhaps present in Tunisia) would be practically invunerable to 2 pdrs and 37mm, and require the heavier 6-pdr and 75mm to deal with at all. The naval formula would be accurate instead of off not just by a smidgen, but wrong in the sign of the effect of multiple plates - a most unlikely error. The German practice of going to uniform plates in subsequent models would be sensible and efficient rather than stupid.

In short, a whole mass of tactical reports, armaments decisions, and official estimates of armor effects would have to be completely wrong. The alternative only requires that someone has mixed up the combined plate effect of 30+50 with that for 30+30. Occam's razor suggests the latter is the more likely explanation for the 69mm figure.

[Lee]

rexford:

Have you presented these interesting findings to Charles? This would have

a significant impact on armor penetration for any affected tanks.

[rexford]

In response to Jason C, firing tests show that a 32mm face-hardened plate covering a 30mm face-hardened plate resists like a 69mm face-hardened plate. This isn't an equation result, and it was 32mm over 30mm.

With face-hardened armor the very hard and thin surface layer provides most of the resistance, and there are TWO face-hardened layers that need defeating on the PzKpfw IIIH hull front.

With homogeneous armor, the surface layers are weaker, so 32mm over 30mm is much less than 60mm.

Firing tests against PzKpfw IIIH show that 32mm/30mm (both face-hard) resists like 69mm face-hard.

When 32mm is bolted over 30mm, angled hits tend to bend the studs holding the plates and create a maintenance headache. Easier for Germans to use a single 50mm plate, which also weights less and allows PzKpfw III to maintain excellent mobility.

Germans could weld 32mm face-hard over 30mm face-hard, but high hardness armor does not weld very well.

Lee:

Charles and company have a copy of our book where we discuss the PzKpfw IIIH layered face-hardened armor (32mm/30mm) which resists like 69mm face-hard.

One question that Jason brings up is how many PzKpfw IIIH fought on the Eastern Front. It sometimes sounds like most were in Nord Afrika. The stories that Jentz provides give T34 tanks a 1200m to 1600m stand-off range against PzKpfw III and IV, where the 76.2mm rounds will easily penetrate German frontal armor.

The 76.2mm will penetrate 50mm face-hardened frontal armor at about 1600m without much trouble, and easily defeats 30mm frontal armor. The 32mm/30mm layered face-hard armor might not be penetrated beyond 1000m by a T34, but a few large caliber hits from 76.2mm might damage the studs.

The PzKpfw IIIH turret front is extremely vulnerable to 76.2mm hits at any range.

The Germans manufactured:

435 PzKpfw IIIF

550 IIIG

308 IIIH

1,549 early IIIJ with 50mm L42

1,067 IIIJ with 50mm L60

903 IIIL and IIIM

Note that IIIH is smallest group from factories, although quite a lot of the IIIF and IIIG were converted to IIIH via added armor on front.

The Jentz stories about T34 vs PzKpfw III and IV are mid-1942, which is when IIIJ were being mass produced.

It is interesting that Jentz does not talk about the panzer units moving IIIH models to the head of the groups due to better armor. Maybe the two or three situations described in Jentz regarding how T34 ripped up panzers related to IIIG and IIIJ tanks (with few, or no, IIIH).

There just isn't enough information to say that a T34 could or couldn't penetrate the front hull of a PzKpfw IIIH beyond 1000m. I can't recall ever seeing a picture of a PzKpfw IIIH on the Eastern Front, although they must have been there.

If PzKpfw IIIH was on the Ostfront, they would be a small percentage of the mid-1942 tanks.

[Lee]

rexford:

I was referring to the difference in resistance between two homogeneous armor

plates and one thick plate of equal thickness to the two plates. Since you say

you got this info. just recently, I assumed that it perhaps was not included in

the book. And thus you would have to give this new information to Charles

separately, so he could consider it for inclusion in his armor modeling.

This lower penetration resistance for extra bolted on homogeneous plates, as

opposed to one thick homogeneous armor plate, makes a big difference in whether

a tank gets penetrated in many situations, if it uses such armor. This new

information could mean one of the most significant improvements to the armor

penetration modeling in CM that has happened in quite awhile.

[M Hofbauer]

Jason,

two face-hardened plates give more resistance for the reasons I originally pondered about above. If you never worked with metal yourself, then use your common sense. It's just the way it is when we are talking face-hardening.

The only thing I am concededly not sure about is if and what kind of face hardening the germans used on different armor, be it original armor or add-on armor added later.

Even then, it still makes sense to produce homogenous plates instead of add-on armor. Homogenous armor still has many advantages over bolt-on armor. For one, the bolted-on armor might tend to break off completely and therefore provide very little additional protection at the areas near the edges. Second, in contrast to a solid cast full homogenous armor, the bolt-on armor does not add to overall structural integrity, but to the contrary it adds an additional strain on the underlying skeleton. And, as Jason pointed out, face-hardened add-on armor doesn't handle too well.

The historical aspect which you are raising has its merits but is not conclusive either. The point whether the germans did or did not use or produce a certain thing does in itself not neccessarily reflect actual facts. For example, the application of Zimmerit onto all german armor in 1943/44 should - using your logic - prove that the allies made extensive use of magnetic attached mines, while we all know they never really did.