Question About Armor Penetration Figures

Why do so many folks on the Internet and in print persist in using armor penetration figures when discussing the relative merits of various armored fighting vehicles and armor-piercing ammunition without taking into account the inescapable effects of obliquity?

Comments on this phenomena, and its rather profound effect of creating wide-spread misconceptions about armor and anti-armor weapons during WWII would be very much appreciated.

Five-Zero-Nan

 

You're right, obliquity is very important. However what happened was that the several countries made a number of tests at different times, and as it was to be expected methods varied immensely so you don't have a common yardstick. Some tested at vertical, others at 30º, etc.

Anyway, for small inclinations I'd hazard you can use the inverse of the cosin (1/cos alpha) as a correcting factor, provided you know what the original inclination was, of course

 

Za,

Thank you for the reply.

Of course, my question was really directed at the near complete disregard for the effects of obliquity when discussing armor penetration figures. The lack of commonality of test results are irrelevant to the question as posed.

"Anyway, for small inclinations I'd hazard you can use the inverse of the cosin (1/cos alpha) as a correcting factor, provided you know what the original inclination was, of course "

Your attempt at humor is appreciated, however, it might also be seen as a signal to others that the question is too unimportant for further, more serious consideration. Was that your intention?

Five-Zero-Nan

 

Well, I added that sentence in all seriousness. In the absence of data there is this simple formula for a horizontal aspect thickness correction factor...

What's your purpose, by the way?

 

Well said on that mate, but I'd place it amongst many other real world factors, both mechanical &, perhaps more importantly, human, that get so easily cast aside by those obsessing over any sort of blank figures.
The physical conflict (any conflict) was fought on this notoriously chaotic planet in a huge range of conditions by frightened men in a horrible whirl of steel, fire, & smoke, never on a sheet of paper .

Cheers,
Adam.

 

Za, Sorry if I misunderstood. I thought you were making fun of my question.

My purpose was to start a serious thread about the general misunderstanding and misues of penetration figures. For example, US Army penetration figures were obtained firing at armor with a zero slope relative to the projectile. In fact, the formula you gave was one of the tools used to estimate US Army anti-armor penetration figures at various degrees of slope, and its use gave alarmingly optimistic, grossly inaccurate results. Accurate models have only come into being relatively recently, and require very sophisticated forumlas manipulated by supercomputers.

So, someone cites a claim that because a certain round will penetrate x amount of armor at a certain range, and that is then taken to mean that the same round will penetrate the armor of a given tank at a certain range. I've seen these discussions go on and on, but they are meaningless unless the effects of obliquity are taken into consideration. And no one seems to do this.

Sorry if I offended you.

Five-Zero-Nan

 

Adam,

Thank you for the reply. I agree wholeheartedly with what you are saying. My point is that penetration effects on the battlefield can only be properly understood if obliquity is taken into account. If a particular round does not penetrate a given tank at a given range, it often did not match the published (advertised) penetration figures. This leads people to discount or ignore the eyewitess accounts, blame the tank crews for some sort of error or lack of training, etc. In doing so, most, if not all of the people discussing penetration fail to appreciate what is really happening amidst the "frightened men in a horrible whirl of steel, fire & smoke."

Five-Zero-Nan

 

I'm not by any means offended, misunderstandings exist to be cleared and that's what happened to this one.

The formula I gave you as I said is the rougest thing, and again it is valid only for small variations in obliquity. As obliquity increases you have to take into account the shape of the projectile (sharp or blunt nosed), composition (rigid, capped, etc), whehter the plate is face hardened or not, and so on, and so on.

As if all this is not complicated enough, you have to think that as you go away from the firing range that you won't be firing at a target facing squarely at you. The target will be pointing towards you in a general sense, yes, but in a multiplicity of angles, more ore less inclined towards you or any other direction. All this plays complete havoc with the prettiest of formulas.

 

Aha! You've just stated the problem with obliquity in armor penetration on the battlefield much better than I have. Thank you and Well done!

Well, what does it all mean? Penetration figures mean absolutely nothing on the battlefield. (Which is just what Adam was getting at earlier.) What I know is that it was rare indeed for a 76mm Sherman firing HVAP (when it actually had some to fire) to knock out a Panther from the front at any range over about 300 yards, and that was only if you had him directly head on. Any sort of angle from his centerline (more obliquity) would result in a bounced round. On the other hand, the Panther could pop a hole in your Sherman from just about any angle, and almost any distance. (The limitation here is that he was close enough to actually hit you.) Sure you could take out a Panther or Tiger from the side, but a normal combat ranges you had to hit a pretty small spot dead on to get penetration. Thank god for the M36 with the big 90mm gun!

Five-Zero-Nan

 

Well, they do mean something after all or else you would not be contrasting the 76mm to the 90mm as you did.

What I wanted to mean was that once you leave the firing range and come out on the battlefield, variables become so many that the mathematical model immeately becomes chaotic. Nothing you can do about this, just hope you carry the biggest stick in the neighbourhood, and if you don't then hope your commanders wold have tailored tactics according to the means available. That's the most important factor.

There was at least an instinctive knowledge of this matter. I remember reading memoirs (don't ask me where, I have no idea now) of tank commanders coming out from hiding and adjusting the tank orientation to the likely threat direction, swinging just about to increase front obliquity but without unmasking side armour too much. What a quandary!

 

What's your idea of normal combat ranges in Western Europe?

How often do you think Panthers got hit on the front with HVAP? If this is a rare event then saying that they were taken out is rare is meaningless.

 

Don't forget the deflection shot (moving vs something moving), and hitting it (while moving)(called "English" in pool/ping-pong/tennis).
Gotta love HEAT/APDS.

 

This is such a complex question. There are alot of variables in play here not just slope of the armor in relation to the striking angle of the shot. The composition of the armor and its heat treating methods play a role, as does the actual thickness of the plate itself.
For example a Panther's glacis is 80 mm thick and composed of face hardened, but not super hard, steel. A US 105mm howitzer using a heavy case HE shell at ranges up to about 400 yards can usually smash a large hole in that plate. Why? Because the 80 mm plate under the combination of impulsive load of the shell hitting the plate and the impulse of the explosion are sufficent to over-stress the plate and cause brittle fracture.
This is a different mechanism from a penetration by shot.

 

If you will go back and look at my orignal, unedited statement, I said that the small spots where you had to hit the Panther and Tiger were on the side of the tank not the front. This was extremely difficult to do at normal combat ranges and under normal combat conditions, so it was a rare event when it happened.

Five-Zero-Nan

 

I just finished a long, glowing, and beautifully written (not really) reply to all of you, but it disappeared when I submitted it, and I was suddenly logged off again. I will start composing my replies in MS Word so they won't be lost.

In short, I would like to thank everyone who has added their comments. For what little it might be worth, I am very impressed with the level of knowledge you all seem to have. It is clear that you are an intelligent group of folks who really love WWII history.

Five-Zero-Nan

 

Five-Zero, the entire side and rear of a Panther is vulnerable to penetration by a Sherman 75mm, T 34/76 F 34 gun or 6 pdr at ranges approaching 1000 yards. The vehicle has relatively thin armor everywhere (45mm for the most part) except up front. In Russia where the ranges on the steppe were often fairly long this worked well. In closer fighting in Western Europe or Italy it didn't.
The Tiger was a different proposition. It had 80mm on the side and rear, generally enough to stop a penetration except at very close range.
As an aside, alot of US tankers came up with a different solution to their problem of fighting the heavier German tanks. They would first fire a white phosporous (WP) round into the vehicle. This would blind the German tank and also cause a gas-effect when the acrid smoke was pulled into the vehicle by the ventilation system choking the crew temporarily. This allowed the US tank the option of withdrawing or pumping another half dozen rounds into the German before he could get a shot off usually with eventually deadly effect.
In tank-on-tank actions the US and, to a lesser extent it seems, British crews also became very good at being quick on the draw. In a great many actions they got the first round off and were first on target. While this may be discounted by those who would say "well, it didn't penetrate" a tank getting hit by a round is not something most crews would shrug off. Very veteran crews might but your average crew is more likely to exhibit some degree of panic over being hit. The first round hit is a powerful advantage.

 

Did read that towards the end of war also the German tank crews were naturally quite poorly trained and on several occasions left the tank after being hit by the WP round thinking the tank was lost by a direct hit.

 

T.A.,

Thanks for the comments. I may be confusing the small spot thing with the Tiger, but will have to talk with a buddy who can jog my memory a bit. Of course, the whole obliquity thing comes into play even with 45mm armor so I don't know that the guns you mentioned would always penetrate. I mean, what are the odd of having the enemy tank at exactly a 90 degree angle to your gun, and being at the same or nearly the same elevation? As you said earlier, "complex."

Shermans were quicker on the draw because of the hydraulic powered turret. Faster than the electric version.

Firing WP was an act of desperation, and was it usually followed by the tank that fired it getting the hell out of Dodge.

Five-Zero-Nan

 

Even if a round did not penetrate, it can cause a concussive effect on the inhabitants. Blinding the enemy tank with WP can allow the Sherman to get on the side where they could do more harm. And it is not necessary to destroy a Tiger. If the tracks can be damaged, it limits the Tiger's ability to manuever. However, this tactic only works when you have a lone Tiger. In the end, it all boils down to who can bring the most effective firepower at the proper time.