Differing Penetration Requirements? JasonC or Rexford?

[c3k]

Gents,

I'm certainly aware of your differing opinions and I certainly do not mean to start any kind of unpleasantness. I would appreciate the favor of you sharing some of your knowledge. For the sake of this forum, please try limit your responses, if any, to your knowledge/opinion of the following: what was the difference between German and Soviet penetration testing results?

I seem to remember that every country used slightly different testing criteria. Then, using the results of the actual tests, the country would extrapolate ballistic performance over various ranges and angles. How the test was conducted, and how the performance was extrapolated to non-test points would both result in differing interpretations of performance for the same weapon and round. Also, the required performance for penetration would cause differing results. (I.e., does penetration mean the entire mass of the projectile passes completely through the armor, or does penetration merely require a pin-hole of light to be visible through the armor?)

Thanks,

Ken

[jacobs_ladder2]

I came across this article the other day. It is a comparison of several sources written by John Salt. The introduction (admittedly in an abbreviated form) is very interesting. Here goes:

To be useful, armour penetration figures should specify not only the gun, range and penetration

achieved, but also the ammunition nature and model fired, the angle of impact, the type of armour attacked and the penetration criterion used.

I believe that the usual British penetration proof criterion early in the war was to have the complete projectile length pass through the target plate on 80% of proof shots fired. Later, some tables give the "critical thickness" of armour, that is, the one for which a shot win and a plate win are equally likely.

The Russians used two penetration criteria, the "Army" criterion requiring complete perforation of the plate, and the more demanding "Naval" criterion requiring the

complete projectile to pass through.

Few, if any, sources provide all this information. An additional annoyance is that some sources are obviously mistaken or misprinted in places.

The customary angle of impact when quoting penetration performance is 30º from the vertical, but some American weapons are quoted for 20º. German practice was (and current NATO practice is) to measure angles from the horizontal, so where 60º is stated, it is usually safe to assume that 30º from the vertical is

intended.

In action, unless firing from exactly right-angles to the target vehicle, there will be an

additional angular component depending on the target tank’s facing. A table for rough conversions from sloped armour to an equivalent thickness of vertical plate is given as one of the extracts from WO 185/118; it will be seen that well-sloped armour seems to be more effective than would be indicated by a

simple cosine calculation.

It is also traditional to quote penetration against homogenous armour. Performance against facehardened plate, especially for smaller weapons firing uncapped rounds, can differ greatly. Armour hardness may vary considerably. For example, according to Kenneth Macksey's "The Guinness Book of Tank Facts and Feats" (Guinness Superlatives, Enfield, 1972), British homogenous armour at the outbreak of WW2 came in "soft" (machineable) and "hard" grades with Brinell hardnesses of 380 and 450 respectively, while Vickers Cemented armour had a Brinell hardness of 600 on the front and 400 on the back. 50 Brinell points corresponds to 10 tons per square inch; 1 Brinell point corresponds by my calculations to 0.315 Kg/sq. mm, or to put it another way 1 Kg/sq. mm is equivalent to 3.17 Brinell points.

It seems that there is a certain velocity band which face-hardened plate protects against best, and for projectiles arriving outside this velocity band, face-hardened plate is less effective than the same thickness of homogenous armour.

Even when sources of variation are accounted for, authoritative sources can seem to disagree. Consider the German 75mm PaK40, a common and well-documented weapon, firing PzGr 39 against homogenous armour at 30º at 500 metres (or 600 yards, which is near enough). Even discarding the highest and lowest observations as outliers, we find a variation between 90mm and 106mm, a difference of 17% of the lower figure. This highlights the point that armour penetration is far from being a deterministic phenomenon, and giving penetrative performance in millimetres (and even in some cases half-millimetres) suggests a degree of precision that does not really exist, even for proof shots fired under tightly-controlled conditions. Performance in the field, of course, is subject to very much greater

variation. As Shelford Bidwell says in "Gunners at War", "All simplified tables showing the

performance of anti-tank guns are misleading". The Bovington booklet "Fire and Movement" says

"Chance also causes discrepancies — for instance, a normally certain penetration may be prevented by

the deflection away of a projectile on a lifting-lug projecting from a turret; conversely, a normally certain immunity may be removed if that same type of projection deflects a projectile towards the armour at a different angle".

Using penetration tables takes no account either of behind-armour effect following penetration, nor of non-penetrating damage. In principle, penetrating shell with a bursting charge should have better behind-armour effect than solid shot, but whether this matters in calibres above about 50mm seems highly questionable. The most supremely futile attempt to improve behind-armour effectiveness must surely be the German inclusion of a small tear-gas pellet in the AP bullet for the PzB 39 anti-tank rifle. It should still be borne in mind that most of these figures generally indicate the thickness of armour the

projectile will just penetrate; the greater the degree to which the armour is overmatched, presumably, the greater will be the damage potential of the penetrating projectile. Hollow-charge weapons are a special case, in that the projectile itself does not penetrate the armour, but rather the jet formed by its charge does. Hollow charge weapons of the WW2 epoch were reputed to have less-than-ideal behind-armour

effects. As the Bovington "Fire and Movement" booklet points out, "If the projectile is not an

appreciable overmatch for the target, however, the penetration can be small enough to do little damage".

Penetration tables also take no account of non-penetrating damage. The running gear of all vehicles canbe vulnerable to AP or HE fire from nearly all calibres. Extremely large calibre rounds can cause catastrophic damage without needing to penetrate the target; a Soviet 122mm shell, for example, might completely remove the turret of its target. Germany and Russia began using welded construction in the 1930s, but Britain and America continued to use rivets until the beginning of WW2. A shot hitting an exposed rivet-head could cause the rivet shank to break off and be projected into the tank, causing

damage. The British continued to use rivets in the Cromwell until the end of the war, but these were tapered to prevent this happening.

I have the article on PDF (193kb) if anyone would like a copy. It contains somewhere in the vicinity of a hundred tables from a slightly lower number of sources. Very useful.

Cheers

Paul

[WimpBastard]

The armor counted to be penetrated if at least 75% of a projectile's fragments happened to be found behind the armor plate. Most of the Soviet armor penetration tables based on this value. Curiously, but the German way of calculation the armor penetration was based on 50% penetration. That's why the Soviet and the German penetration values are so different.

From Battlefield.ru

[c3k]

Gents,

Thanks!! Anyone else have anything to add?

Ken

[jacobs_ladder2]

Also just came across this and thought you guys might want to have a look at it. Appears to be various penetration formulae. Awesome site if you can read Russian, btw, but luckily this page is in English.

Cheers

Paul