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Go Back   Armchair General and HistoryNet >> The Best Forums in History > Historical Events & Eras > World War II > Armor in World War II

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Armor in World War II Discuss all aspects & disciplines of World War II Armor here.

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  #286  
Old 25 Mar 12, 17:03
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I think the thing the US got right more than anything else was the basic engineering. Their tanks had a single turret ring size and design. You could plop any turret on any hull for all intents. The M36B1 is a perfect example. Take an M36 turret and put it on a Sherman hull.
The periscopes were interchangable. Tracks, suspension, engines, transmissions, all interchangable.
The Soviets got to the same result by simply minimizing types in use to basically three hulls, a light (T70) medium (T34) and heavy (KV 1 / IS).

Britain and Germany were saddled with a variety of AFV designs with few really interchangable parts. It adds expense and does nothing to help maximize production.

The Allies also saw the advantage to using lots of large castings. German industry post WW 1 lost that capacity so they stuck with plate for the most part. But, even then they did some things that weren't particularly wise from a production point of view. A good example is the Tiger I turret. That horseshoe plate that forms the sides is a horribly hard piece to make. The roll forming machine had to be gigantic just to make it. That creates a bottleneck as you will never have more than one or two to make that part.
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  #287  
Old 25 Mar 12, 21:58
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Quote:
Originally Posted by dutched View Post
I wrote this before:
[U]To be honest the question arises why the Sherman hull was not re-designed before it went into production as it hull is basically the M3 hull with a re-done front bit.
It is my understanding that the lower portion of the Sherman hull was adopted from the M3, but the upper was entirely new.
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  #288  
Old 25 Mar 12, 22:58
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Originally Posted by Sleepy Head View Post
It is my understanding that the lower portion of the Sherman hull was adopted from the M3, but the upper was entirely new.
The chassis was originally developed for the M2 Medium tank. As was the drive train and many other components. That chassis was reworked into the M3 & reworked again into the M4, the M10 TD, the M7 SP artillery, the M36 TD, the Kanagroo personnel carrier, a tank recovery vehical, and few others I missed.

The M2 chassis, tracks, drive train, & other bits were the culmation of a dozen prototypes and hundreds of small components tested in the previous twenty years. One might say the M4 took two decades to develop

This was not much different from many other US weapons in WWII. The M2 105mm Howitzer was modified from a design tested in the early 1920s. The M1 155mm Howitzer was a updated version of US modifications or earlier French designs. The M1 Garand rifle was originally tested in the mid 1920s and tinkered with over the next fifteen years before mass production started.
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  #289  
Old 26 Mar 12, 00:23
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Quote:
Originally Posted by Sleepy Head View Post
Thank you for the additional explanation.

I understand the concept.

Here’s my problem. I cannot locate a single formula for armor penetration that does not take mass, striking velocity, angle of attack, etc., into account. The definition of overmatch, as written, cannot be expressed mathematically, and that means there is something very wrong with it. What, for example, is the minimum striking velocity and mass which will allow an overmatching shot to penetrate the target armor? According to the definition there is none.
FWIW, Ogorkiewicz mentions overmatching in his Technology of Tanks: "The use of [electroslag remelted steels] also greatly reduces spalling when armour is perforated by an overmatching projectile..." Bird and Livingston also make an attempt at explaining overmatch using the de Marre equation in their book (although I have seen some of their work questioned):
Quote:
When armor thickness exceeds steel projectile diameter, shear resistance is sufficient to minimize plug ejection and the projectile must push its way through armor, which requires considerably more energy than shear failure...If plate thickness is 25mm and projectile diameter is 50mm, kinetic energy for 50% penetration success is equal to 0.38K. Against a 75mm thick plate, the 50mm round would require kinetic energy equal to 1.76K, where tripling the plate thickness (25mm to 75mm) increases energy requirements by a factor of 4.63 (1.76/0.38). Energy requirements increase faser than plate thickness due to a shift in the primary failure mode from plugging to pushing armor out of the way.
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Originally Posted by Carl Schwamberg View Post
This hull design remained the basis for US medium tanks through the M60 series.
Or the M47, at least.
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  #290  
Old 26 Mar 12, 02:03
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Quote:
Originally Posted by DogDodger View Post
FWIW, Ogorkiewicz mentions overmatching in his Technology of Tanks: "The use of [electroslag remelted steels] also greatly reduces spalling when armour is perforated by an overmatching projectile..." Bird and Livingston also make an attempt at explaining overmatch using the de Marre equation in their book (although I have seen some of their work questioned):

“When armor thickness exceeds steel projectile diameter, shear resistance is sufficient to minimize plug ejection and the projectile must push its way through armor, which requires considerably more energy than shear failure...If plate thickness is 25mm and projectile diameter is 50mm, kinetic energy for 50% penetration success is equal to 0.38K. Against a 75mm thick plate, the 50mm round would require kinetic energy equal to 1.76K, where tripling the plate thickness (25mm to 75mm) increases energy requirements by a factor of 4.63 (1.76/0.38). Energy requirements increase faser than plate thickness due to a shift in the primary failure mode from plugging to pushing armor out of the way.“
In my humble opinion, the information you provide is worth quite a lot, and I thank you for it.

I assume that the equation you mention is either the Milne-de-Marre, or the Marre. Without seeing the source you mentioned I cannot tell. These equations are unable to fully describe the complexities of armor penetration, but are reported to serve as a good starting point assuming their limitations are recognized.

There is no mention of slope or angle of attack in the second quotation you provided. Both are interrelated and both have a significant effect on the ability of a projectile to penetrate armor. Since it is well established that increasing the slope of the armor will increase its resistance to penetration, and that angle of attack has a similar effect, although the total effects of these are unknown to me, we might safely assume that overmatching shot as described on weaponsofwwii.com (?) would also require significant increases in kinetic energy to overcome the increased resistance of armor under these two factors. (All this has given my a headache.)

Anyhow, thanks for the information. I will take responsibility for the headache because in trying to make sense of all this I have badly overtaxed the abilities of my poor noggin.
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  #291  
Old 26 Mar 12, 02:07
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Originally Posted by Sleepy Head View Post
Anyhow, thanks for the information. I will take responsibility for the headache because in trying to make sense of all this I have badly overtaxed the abilities of my poor noggin.
Mine too, but I tend to let go before it becomes too painful.
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  #292  
Old 27 Mar 12, 13:58
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Quote:
Originally Posted by Sleepy Head View Post
It is my understanding that the lower portion of the Sherman hull was adopted from the M3, but the upper was entirely new.
We are probably talking about the same thing in different wording.
What I meant with the front bit, is the part in front of the engine compartment. I reckon you mean the same part.

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  #293  
Old 28 Mar 12, 02:40
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Quote:
Originally Posted by Sleepy Head View Post
In my humble opinion, the information you provide is worth quite a lot, and I thank you for it.

I assume that the equation you mention is either the Milne-de-Marre, or the Marre. Without seeing the source you mentioned I cannot tell. These equations are unable to fully describe the complexities of armor penetration, but are reported to serve as a good starting point assuming their limitations are recognized.

There is no mention of slope or angle of attack in the second quotation you provided. Both are interrelated and both have a significant effect on the ability of a projectile to penetrate armor. Since it is well established that increasing the slope of the armor will increase its resistance to penetration, and that angle of attack has a similar effect, although the total effects of these are unknown to me, we might safely assume that overmatching shot as described on weaponsofwwii.com (?) would also require significant increases in kinetic energy to overcome the increased resistance of armor under these two factors. (All this has given my a headache.)

Anyhow, thanks for the information. I will take responsibility for the headache because in trying to make sense of all this I have badly overtaxed the abilities of my poor noggin.
Overmatch can be described by the de Marre-based equations commonly seen today, e.g., from Ogorkiewicz in Design and Development of Armored Vehicles: wv^2 = (kd^3) ([t/d]^n)

w = projectile weight; v = projectile velocity; t = armor thickness the projectile just perforates; d = projectile diameter; k, n = constants

Apologies for poorly formatting it in the forum. Ogorkiewicz says that for "typical projectiles and armour plates," k is ~10^6. The constant n = 1 if we assume the projectile's KE is absorbed in a constant normal stress (which will push armor out of the way to the sides) and 2 if we assume the projectile creates a plug equal to its diameter by inducing constant shear stresses. The actual value for n, of course, is somewhere in the middle and depends on the projectile and target plate used (n = 1.41 for 20 pounder APCBC versus RHA, and 1.37 for 105 mm gun M68 APDS versus RHA).

That equation asserts that it takes less energy (wv^2) to penetrate armor if we make the ratio of armor thickness to projectile diameter smaller; that is, if we make the projectile diameter relatively larger than the armor thickness. Also, for a given amount of energy, the n constant will be a larger value (i.e., closer to perfectly pushing a cylindrical plug of armor into the tank) if the t/d value is smaller. Bird and Livingston assert that plug formation is the lower-energy form of failure, and liken it to knocking a hole in drywall with a hammer. If the t/d value is larger, n will be closer to 1, which indicates the projectile will have to push armor laterally out of its way instead of forming a plug.

Anyway (keeping in mind the limitations of these equations, as you have noted), this shows that a larger diameter projectile will penetrate more armor than a smaller diameter at a given velocity.

Slope can increase the linear thickness of armor and large angles can increase a projectile's tendency to shatter or ricochet, but slope in itself doesn't necessarily increase resistance to penetration. Indeed, APFSDS projectiles can normalize themselves to sloped armor, rendering slope of up to 70 degrees or so irrelevant. Blunt-capped projectiles like those used by the USSR in WW2 are also more effective against sloped armor than more ogival projectiles.

I'm no ballistician, however, and my references would probably have to defer to your study of "several fairly serious works on military ballistics."
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  #294  
Old 28 Mar 12, 03:48
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Apparently another thing about overmatching, if this hasn't been mentioned already, is that if the calibre of the projectile exceeds the nominal thickness of the armour (as opposed to the thickness due to angle), then in all likelihood the armour will be penetrated, thickness due to angle be damned.
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  #295  
Old 29 Mar 12, 00:22
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Quote:
Originally Posted by DogDodger View Post
Overmatch can be described by the de Marre-based equations commonly seen today, e.g., from Ogorkiewicz in Design and Development of Armored Vehicles: wv^2 = (kd^3) ([t/d]^n)

w = projectile weight; v = projectile velocity; t = armor thickness the projectile just perforates; d = projectile diameter; k, n = constants

Apologies for poorly formatting it in the forum. Ogorkiewicz says that for "typical projectiles and armour plates," k is ~10^6. The constant n = 1 if we assume the projectile's KE is absorbed in a constant normal stress (which will push armor out of the way to the sides) and 2 if we assume the projectile creates a plug equal to its diameter by inducing constant shear stresses. The actual value for n, of course, is somewhere in the middle and depends on the projectile and target plate used (n = 1.41 for 20 pounder APCBC versus RHA, and 1.37 for 105 mm gun M68 APDS versus RHA).

That equation asserts that it takes less energy (wv^2) to penetrate armor if we make the ratio of armor thickness to projectile diameter smaller; that is, if we make the projectile diameter relatively larger than the armor thickness. Also, for a given amount of energy, the n constant will be a larger value (i.e., closer to perfectly pushing a cylindrical plug of armor into the tank) if the t/d value is smaller. Bird and Livingston assert that plug formation is the lower-energy form of failure, and liken it to knocking a hole in drywall with a hammer. If the t/d value is larger, n will be closer to 1, which indicates the projectile will have to push armor laterally out of its way instead of forming a plug.

Anyway (keeping in mind the limitations of these equations, as you have noted), this shows that a larger diameter projectile will penetrate more armor than a smaller diameter at a given velocity.

Slope can increase the linear thickness of armor and large angles can increase a projectile's tendency to shatter or ricochet, but slope in itself doesn't necessarily increase resistance to penetration. Indeed, APFSDS projectiles can normalize themselves to sloped armor, rendering slope of up to 70 degrees or so irrelevant. Blunt-capped projectiles like those used by the USSR in WW2 are also more effective against sloped armor than more ogival projectiles.

I'm no ballistician, however, and my references would probably have to defer to your study of "several fairly serious works on military ballistics."
Thank you for the extensive description and discussion. It is most interesting and gave me a lot to think about.

Before I start, I would like to point out that while I have studied several fairly serious works on military ballistics, I cannot claim to have absorbed, but a small fraction of what they have to say, and even that is tenuous since when I think I have figured something out it just raises more questions than it answers.



This sentence seems to get a the crux of the matter which is the amount of energy the projectile can deliver to and into the armor at, as you say, a given velocity.

Anyway (keeping in mind the limitations of these equations, as you have noted), this shows that a larger diameter projectile will penetrate more armor than a smaller diameter at a given velocity.

The problem is that many people appear to think that overmatching is a constant. They do not account for the differences in striking velocity, mass, angle of attack, shell design, and other things. They reduce a complex issue down to a very simple set of variables and constants which do not accurately reflect the realities of the battlefield, and then speak of overmatching as an absolute “law” or “rule.”

My problem is how to explain my understanding of this problem, and why overmatching is not the constant that so many seem to believe. Maybe by holding the thickness and type of armor as a constant, and using the exact same overmatching projectile I can demonstrate the fallacy of the overmatching concept as it pertains to the claimed ineffectiveness of sloped armor.

I will use the 90mm M82 APC round with the muzzle velocity of 2,670 f/s.

This round overmatches 3 inches (76.2mm) of armor by a factor of 1.18 (rounded).

The 90mm M82 APC round will penetrate 3 inches of RHAP with a slope of 20 degrees at a range of approximately 3,750 yards with a striking velocity of 1,800 f/s.

However, the 90mm M82 APC round cannot penetrate 3 inches of RHAP with a slope of 55 degrees at any range. It can penetrate slightly less than 2.5 inches of RHAP with a slope of 55 degrees at a range of 500 yards with a striking velocity of about 2,550 f/s.

The conclusion here is self evident. The penetration capability of an overmatching projectile decreases with slope. This is the exact opposite of the common understanding (see following quotation for an example) that increased slope has no, or minimal protective effect when hit by an overmatching projectile.

Quote:
Originally Posted by broderickwells View Post
Apparently another thing about overmatching, if this hasn't been mentioned already, is that if the calibre of the projectile exceeds the nominal thickness of the armour (as opposed to the thickness due to angle), then in all likelihood the armour will be penetrated, thickness due to angle be damned.
My source for the 90mm values is Terminal Ballistic Data, Vol. III. Office of the Chief of Ordnance, September 1945.

It is important to keep in mind the above penetration figures do not take into account the additional effects slope on rounds striking at oblique angles which further increase the effective slope of armor.
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  #296  
Old 29 Mar 12, 00:57
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Quote:
Originally Posted by Sleepy Head View Post
Thank you for providing the interesting article.

After taking some time to digest it, I have arrived at the following.

According to the article, “Impulse Loading of Armour by High Explosive Squash Head Munition,” impulse loading creates a transient wave which produces the phenomena known as scabbing or spalling. Spalling has been well known for a very long time, but “the impulse loading or armour has not been reported in a detailed and organized manner, and only fragmentary reports have appeared in the literature.” This alone suggests the overmatch definition lacks sufficient detail or organization to be reliable.

Beginning with the definition of overmatch from the website cited in a previous post, http://www.weaponsofwwii.com/armour-...ary-metallurgy, I see the following.

When the thickness of the armour plate is less than the diameter of the shot fired at it, the shot is said to overmatch the armour plate. When a shot overmatch the plate, the stress on the steel increases. For flat-nosed low-energy shots, this can result in a plug being punched from the armour plate by the shot, rather than the shot pushing through the plate. Especially hard armour plates are likely to plug formation when overmatched. (WAL 710/492)

For this reason, overmatching shots will be significantly more likely to penetrate an armour plate than a matching or undermatching shot than the increase in shot size alone would indicate.


Please note there is no mention of spalling (scabbing), projectile mass, striking velocity, angle of attack, the type of explosive round, the amount of the explosive charge (if any), or any direct, clear reference to high explosives or solid shot. Only one constant is mentioned, the diameter of the projectile must be greater than the thickness of the armor plate. There are also references to “flat nosed low energy shots” and “plug formation” when “especially hard armour plates are overmatched,” but no specific mention of any type of projectile other than “shot.”

The impulse loading article contains several important differences, some of which are significant. Mass (charge to mass ratio), length of projectile to diameter, striking velocity, angle of attack, type of explosive round, and the amount of explosive charge are all referenced as relevant factors, none of which are mentioned in the overmatch definition. Also, the authors were investigating the impulse loading effect of a specific type of high explosive round, not shot as referenced in the overmatching.

This all leads to a singular conclusion. The overmatch definition is missing a large amount of vital information regarding mass, striking velocity, angle of attack, length of projectile to diameter, etc, all of which are critical factors in any attempt to describe (define) the terminal ballistics of projectiles against armor. Barring the appearance of a detailed, complete definition, overmatching has to be viewed as unsubstantiated.
I would disagree with the last. The phenomona is well known and described. What we lack here is simply a mathematical model of its actual working. This might be hard to come by as there isn't going to be consistant data on the impact area with relationship to the shot, its mass, striking angle, and a whole range of other variables. I suspect it is largely uncalculable other than by application of a wide range of formulae tied together then run as a computer model.
Such may exist. Or, it may not. I don't know for sure. But there is plenty of evidence large heavy rounds that shouldn't penetrate a given plate by typical armor penetration formulae do exactly that in one form or another (scabbing, shattering, fragmenting, cracking, etc.,).
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  #297  
Old 29 Mar 12, 17:11
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I would disagree with the last. The phenomona is well known and described. What we lack here is simply a mathematical model of its actual working. This might be hard to come by as there isn't going to be consistant data on the impact area with relationship to the shot, its mass, striking angle, and a whole range of other variables. I suspect it is largely uncalculable other than by application of a wide range of formulae tied together then run as a computer model.
Such may exist. Or, it may not. I don't know for sure. But there is plenty of evidence large heavy rounds that shouldn't penetrate a given plate by typical armor penetration formulae do exactly that in one form or another (scabbing, shattering, fragmenting, cracking, etc.,).
I think the mathematics is the lesser of the missing detail. It can be worked out theoritically. The biggy that is missing here are the mechanical properties of the armour. This can only be derived from original test results.
Anyway for most of us rules of thumb go far enough. Bit like the performance of engines: bHP rating sais everything (very little )

Ed

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  #298  
Old 29 Mar 12, 21:06
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Quote:
Originally Posted by Sleepy Head View Post
My problem is how to explain my understanding of this problem, and why overmatching is not the constant that so many seem to believe. Maybe by holding the thickness and type of armor as a constant, and using the exact same overmatching projectile I can demonstrate the fallacy of the overmatching concept as it pertains to the claimed ineffectiveness of sloped armor.

I will use the 90mm M82 APC round with the muzzle velocity of 2,670 f/s.

This round overmatches 3 inches (76.2mm) of armor by a factor of 1.18 (rounded).

The 90mm M82 APC round will penetrate 3 inches of RHAP with a slope of 20 degrees at a range of approximately 3,750 yards with a striking velocity of 1,800 f/s.

However, the 90mm M82 APC round cannot penetrate 3 inches of RHAP with a slope of 55 degrees at any range. It can penetrate slightly less than 2.5 inches of RHAP with a slope of 55 degrees at a range of 500 yards with a striking velocity of about 2,550 f/s.

The conclusion here is self evident. The penetration capability of an overmatching projectile decreases with slope. This is the exact opposite of the common understanding (see following quotation for an example) that increased slope has no, or minimal protective effect when hit by an overmatching projectile.
You have to be careful here, as the semi-infinite plates used in testing are not subject to the back plate phenomenon to which TA was alluding. Shockwaves bouncing off the rear face of the armor can cause a plate to fail even if it's beyond a projectile's theoretical penetration ability.

I'll agree that an overmatching projectile isn't guaranteed to perforate a given plate simply because of the t/d ratio. High angles of slope can increase the chance of a projectile to ricochet or shatter no matter the t/d relationship, and the larger LOS thickness is not a trivial concern. However, due to larger diameter projectiles causing more severe shock waves through a plate and being more likely to form a plug rather than displace armor laterally, I think it can be said that at a given amount of energy, a larger diameter projectile would have a better chance at perforation.

This discussion only applies to full-caliber armor-piercing projectiles, of course. APFSDS is essentially immune to slope up to about 70 degrees, and a HEAT penetrator doesn't care about slope at all.
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Old 29 Mar 12, 22:14
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Originally Posted by DogDodger View Post
This discussion only applies to full-caliber armor-piercing projectiles, of course. APFSDS is essentially immune to slope up to about 70 degrees, and a HEAT penetrator doesn't care about slope at all.
Just to stir the pot, is this 70° from the vertical or from the horizontal? That always confuses me, much like horsepower — crank or shaft?

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Old 29 Mar 12, 23:52
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Quote:
Originally Posted by DogDodger View Post
You have to be careful here, as the semi-infinite plates used in testing are not subject to the back plate phenomenon to which TA was alluding. Shockwaves bouncing off the rear face of the armor can cause a plate to fail even if it's beyond a projectile's theoretical penetration ability.

I'll agree that an overmatching projectile isn't guaranteed to perforate a given plate simply because of the t/d ratio. High angles of slope can increase the chance of a projectile to ricochet or shatter no matter the t/d relationship, and the larger LOS thickness is not a trivial concern. However, due to larger diameter projectiles causing more severe shock waves through a plate and being more likely to form a plug rather than displace armor laterally, I think it can be said that at a given amount of energy, a larger diameter projectile would have a better chance at perforation.

This discussion only applies to full-caliber armor-piercing projectiles, of course. APFSDS is essentially immune to slope up to about 70 degrees, and a HEAT penetrator doesn't care about slope at all.
It seems important to me that we not characterize the HEAT round as being unaffected by slope. HEAT rounds, at least during WWII, were capable of penetrating armor at a considerably larger angles of attack than shot, but still lost effectiveness beyond certain points. Another factor which negatively effected the performance of the HEAT round was the spin imparted to the projectile by the rifled barrel of the firing weapon.

I am unaware of how the Ordnance Dept. during WWII created its target armor blocks, but suspect it was via the expedient of clamping, which as you imply, was subject to providing misleading penetration results. This said, it cannot be used to discount the reported results unless we can locate something from the Ordnance Dept. that supports this, because clamping does not always create gaps in the armor test blocks.

On a related note, the volume that provided the 90mm APC data includes the following statement which I missed previously.

“The penetration curves are compiled for intact or shattered projectile[s], with the greatest portion of the fragments, completely penetrate the plate.”

This means the Ordnance researchers either did not get spalling, or for reasons unknown, did not include it in the results. Some might wish to claim the second possibility as support for the idea that overmatching projectiles created spalling, and the concept is therefore supported.

Without additional data, this claim would be premature, especially in light of the 90mm APC data which clearly demonstrates that the performance of an overmatching projectile is adversely effected by slope.

It seems in recent posts that the definition of overmatching is beginning to morph into something very different than what is frequently described on this forum and weaponsofwwii.com. To keep the discussion on track I say once again; their definition of overmatching claims that the slope of armor (angle of attack) has no effect on the overmatching projectile whatsoever, and fails to take into account additional factors such as mass, striking velocity and so on.

Physics rules and overmatching drools.
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