"How much does sloped armor really matter?" Topic

I'm really looking for an answer from the engineers / mathematicians / trained tankers.

I understand that sloped armor (1) gives a (slim?) chance of a glancing shot and (2) effectively provides thicker armor in the direction of attack.

So my question really revolves around the "direction of attack." Even a high-velocity gun has some "plunge" to the fire and nearly all attacks will take place at some angle off the perpendicular. Given shots come in "off perpendicular" in two dimensions, how much does sloped armor really help? Seems to me that if you get the slope wrong, it could actually make things worse.

Thanks!

I always wondered about that too. Sure on the gaming table tanks are often exactly on the same level, but how often would that happen in reality? Almost never.

So wouldn't the sloped armour actually not be all that sloped much of the time. Although I suppose sometimes it would be even more sloped.

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A lot in my opinion
think about weight of steel as well
it can deflect shells
look at modern tanks especially frontally
heres an armor thickness calculator
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At a 60 degree slope, armor defends at twice it's thickness; ie., 2 inches of armor protects as though it is 4 inches thick…

And yes Scott, sometimes extreme plunging fire can negate armor slope causing the incoming projectile to act as though it is striking less angled armor. Games like Yaquinto's Armor, Panzer and 88 had charts reflecting this effect…..

With modern kinetic energy penetrators, sloped armor is not much of an advantage, compared with 1960s and earlier penetrators. The reason is that modern APFSDS penetrators are designed to turn into sloped armor. This means that the thinner sloped plates are more vulnerable. It should also be noted that sloped armor has a manufacturing advantage. It's much easier to roll a thinner plate than a thicker one. A sloped plate with the same LOS thickness as a vertical late weighs exactly the same as the vertical plate, so there's no weight savings.

I think it matters a lot – but not all of the time. From what I can see any horizontal/lateral angle less than 25 degrees does not have much effect, about a +15%. Up to 40 degrees is about 150%. Even then it may not be thick enough to matter if the penetration is high enough.

Where it can really matter is when the compound angle is 70 degrees or greater. An example would be sloped armor of 45 degrees coming from a 60 degree angle would be a compound angle of 70 degrees, a good chance of bouncing off even if penetration is high enough. That's when it really matters.

When you get funky horizontal and vertical angles on turrets like the Panzer IV and sloped turret side armor that is vulnerable to frontal shots like the Tiger II, T-34 and Panther it really begins to matter. It can also significantly increase armor thickness hitting the side turret/hull from a front 30-60 degree aspect. A side armor of 30mm with no slope being hit at a lateral 60 degrees is equal to about 75mm.

Aberdeen Proving grounds put out some good info: link

There are other slight variables like the angle the round enters (only a few degrees for most HV tank rounds), tilt and cant of the tank too.

Of course all of this is just a curiosity unless it can be made playable.
Here is a link to some play aids I've been working on using the nomograph from the Aberdeen Proving Grounds and some spreadsheet calculations:
Link: link

This simplifies it for me and has been playable and easy to understand at conventions. It gives some unexpected but realistic results.

Wolfhag

I think the simple fact that the German armies converted to it after their T-4 experience, suggests that there is (or at least was in WWII) a benefit.

When playing around with my own rules, I tend to give sloped vehicles a +1 advantage, which is probably equating to a 10 – 15% advantage. I have no idea whether this is a realistic portrayal, since shot itself comes in from so many angles, but for me, it is just a representative influencing factor.

I remember some article about Swedes horrified with tests from some Russian 125 mm on their S tank that totally smashed them. Hence buying Leo 6.
Very very modern rounds, not much.

I don't think sloped armor was anything really new starting in 1941. French Souma, Char 1, Polish 7TP, Russian T-28 had sloped frontal armor. The T-34 was a nasty surprise because it had the whole package: speed, maneuverability, fire power and protection.

I think you'll find the tanks with the best frontal sloped armor to have the transmission and drive sprocket in the rear. The Germans and Americans had theirs in the front which took up a lot of space. There are advantages and disadvantages to both designs.

I'd be interested in other opinions about how important it is an a tank-tank combat and how you handle it.

Wolfhag

There are a lot of frustrated tank gunners who remember all too well their shot ricocheting off the front glacis and into the sky. Off of T34s, Panthers and even off of the front of Shermans at times.

Of course it doesn't stop everything but it certainly helps.
Kind of like buying insurance isn't it. Take any advantage you can get.

About those S-Tanks, they wouldn't take hits from too much. The modern equivaent of a Hetzer with thin armour.

Hard to compare modern tanks to WW2 tanks. The ammo has changed since the war. In ww2, ammo could be solid shot but not as elaborate as Sabot was. Some HEP was used but in the 1960s-1980s it was regarded as the last choice for shooting at tanks due to its limited effectiveness. A modern round is HEAT which spews a stream of gas through the entry point. Second choice to Sabot.
Slope does affect sabot and Heat but does not affect Hep which explodes on contact. It uses spalling to the inside armor to cause damage.
Sandbags have always been a tankers friend to add protection to a tank or APC.

In WWII sloped armor had a multiplier affect vs. ogive shaped shells. This was somewhat negated by blunt nosed shells. The Russians were the first to employ this in most of their AP shells. The Germans eventually were won over to this but they used a different tact. They used a hard blunt cap instead of a solid shell with a blunt end.

In this Nathan Okin table shows the multiplier for ogive naval shells. I added data point cases from US and Russian tank round tables.

For modern weapons a blunt ended long rod penetrator also negated the slope multiplier affect. Below is a strobe photo of a penetrator at work.

There is another factor that works against sloped armor that is not reflected in the table data. This is the shock effect where a thin plate cracks more easily than a thicker plate.

Thanks folks! Great info and links above.

I like this statement from the answers.com link provided by Halifax49:

If attack were equally likely from all directions, the ideal form would be a sphere; because horizontal attack is in fact to be expected the ideal becomes an oblate spheroid.

Mobius – Thanks for the chart and the info on blunt-nosed projectiles. Saves me asking about that!

According to the AP curves provided in TM9-1907 Ballistic Data Performance of Ammunition (circa 1948), a projectile striking angle of 45 degrees would reduce penetration by approximately one-half compared to a striking angle of zero degrees versus RHA. So inclination of an armor plate at large angles (say 30+ degrees materially improved the degree of protection.

German WW2 reference AP performance data was based upon a striking angle of 30 degrees, which they had deemed to be the overall average striking angle under service condtions (see Jentz on this).

B

According to the AP curves provided in TM9-1907 Ballistic Data Performance of Ammunition (circa 1948), a projectile striking angle of 45 degrees would reduce penetration by approximately one-half compared to a striking angle of zero degrees versus RHA.

You have to be more specific on which gun. My US 76mm data is the M62 ammo from M1A2 gun per the TM 9-1907 graph at 1000yds.

As above, for WW2 era ammo, it made a significant difference. For modern sabot ammo, it makes very little difference at all.

The S-Tank actually had pretty decent armor at the time it was designed, because of the slope. 190-340mm LOS thickness.

Modern long-rod penetrators, however, happily punch right through the 70mm thick glacis and stop in the engine block on the way out the back.

"I remember some article about Swedes horrified with tests from some Russian 125 mm on their S tank that totally smashed them. Hence buying Leo 6."

Not only the Swedes. the performance of the SOVIET issued rounds (as opposed to the widely imported rounds) was a something of a rude shock to NATO. As always, the Soviets kept the best stuff for themselves.

Both the Israelis and USMC use applique armor that is basically .5" thick steel plates spaced a few inches off the principle armor. It's "corrugated" and gives the benefits of sloped armor most of the time (lots of variations on angles of shot vs vehicle vs specific hit location.
In USMC its called Enhanced Applique Armor Kit. I can attest to it's effectiveness in defeating RPG-7 warheads in Iraq when mounted on AAVP-7s. During the march up (2003 Attack to Baghdad) 7th Marines had one AAVP-7 that had a RPG-7 rocket fired at it. The round did not detonate (later turned out that the Bath Party loyalist who were fighting had not pulled the safety wire) and it got lodged in between the EAAK and the regular armor. They continued the attack and had about 30 km after the last fight. They did not notice it until they stopped and the Marines got out.

Do a google image search for applique armor AAVP-7 and lots of photos will pop up. Here are links to a couple:

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About the Strv 103/S-tank tests, what seldom gets mentioned is that the infamous shots that went right through the tanks were fired at ranges than you would not often find in combat. Now the long range shots did worse damage than expected but none of the experts involved thought that the S-tank would do well against the 125mm rounds. After all it was an early 1960's design that was never supposed to soldier on for as long as it did. (It should have replaced around 1982 by a new tank according to the original plans)

Plans for a new tank to replace the S-tank were well underway by the time the tests were carried out, the Leopard was only chosen once the Swedish designed Strv 2000 proved too expensive and time consuming to produce. The choice had nothing to do with the fate of the S-tank when hit by 125mm rounds.

The true shock of the tests were not that the S-tank did not resist 125mm APFsDS well but that the Swedish designed "Pil 80" APFSDS did not penetrate the T-72s front & turret armour at the expected ranges. This led to an emergency purchase of Israeli design 105mm APFSDS to correct a fatal flaw.

Slope matters a great deal. It can turn an obvious kill shot into a harmless ricochet.

Folks,

Thanks for the informative posts with great supporting information!

Special thanks to Wolfhag for the compound angle play aid. Brilliant!!

About the Strv 103/S-tank tests, what seldom gets mentioned is that the infamous shots that went right through the tanks were fired at ranges than you would not often find in combat. Now the long range shots did worse damage than expected but none of the experts involved thought that the S-tank would do well against the 125mm rounds. After all it was an early 1960's design that was never supposed to soldier on for as long as it did. (It should have replaced around 1982 by a new tank according to the original plans)

Yeah, but the 1980s-vintage Soviet-issue APFSDS would still have opened the S-tank like a beer can, nevermind the 1990s-vintage 3rd generation APFSDS.

Mobius wrote – "You have to be more specific on which gun. My US 76mm data is the M62 ammo from M1A2 gun per the TM 9-1907 graph at 1000yds."

I was generalizing from the various graphs. Your 76mm value for the cited projectile/gun @ 1000 yds and 45deg incidence looks good to me. I interpolated factors of 1.76 versus WHA and 1.705 versus FHA.

OTOH, the factors for other US guns/projectile at 1,000 yds and 45deg give higher factors -
57mm APC-T versus WHA is about 1.95
76mm HVAP versus HA is about 2.2

I think it is reasonable to say that the armor factor of merit for a 45deg striking angle lies between 1.7 and 2.0 for the generality of situations, depending upon range, projectile type and armor. It does bear saying, however, that the tanks known for sloped frontal armor (T34, Panther, Tiger II, Sherman) all had slopes that exceeded 45deg (i.e. in the 47-55deg range IIRC).

B

Armymen,
The report date for the compound armor nomo is from 1984. I agree it's brilliant but not my idea. I came across it when doing research to develop a gunnery model for the game system I'm currently working on. I have not seen any games that have used this report to make a play aid for armored warfare. I find that surprising.

Mostly what I've heard from gamers about compound angles is a lot of whining, too complicated, Tractics has tried that and rolling a D6 is accurate enough. So be it. In the game I've developed there can be a potential 100 hit locations per square meter of target facing using a scaled image of the correct target aspect. This means all of the nuances of the armor configuration, slopes and lateral angles can somewhat(?) easily be taken into account. I find that stuff an interesting aspect of armored warfare, others don't.

Each vehicle and aspect is modeled without using complicated hit locations or special damage charts. The benefit to the playing experience seems to be that there are unexpected outcomes where shots that should kill don't and ones that should not hit a weak spot like the hull mg or turret ring. The feedback to the player is exactly what saved or did not save the target rather than just an abstracted missed die roll. You need specific hit locations and take compound angles into account to model that. That's why I'm working on it.

I'm in the small minority of players that like this type of stuff and am trying to make it playable. Using good play aids like the compound angle nomo, graphics and pre-computed armor values for most of the situations is helping but it's still a WIP. Anyone else working on this type of thing?

Wolfhag

Anyone else working on this type of thing?

I'd be surprised if World of Tanks wasn't using that.

IMO, it's too much detail for a player to control more than 1 tank without automation support.

Mostly what I've heard from gamers about compound angles is a lot of whining, too complicated,

Well, yeah, it is. Getting the compound angle is only the start of the problem. You have to find the armor thickness per Halifax's formula then you have to increase that by the proper shell type obliquity effective armor multiplier. It is a large can of worms that is more easily dealt with in the time span of a playable game by an abstract die roll modifier.

Mobius,
There are many steps, no doubt about it. I'm one of the biggest whiners about game mechanics that make you do a lot of calculations. I do think there is a way to calculate the outcomes to a high level of accuracy by just referring to the horizontal angle. Of course it would have to be on a chart or card. It could be in 5, 10 or 20 degree increments. I'm sure someone could come up with something that would fit on a 3x5 or 4x6 inch index card.

Lion in the Stars: WoT probably already has this. They seem to have a pretty good model but I've never played. Next weekend in Sacramento I'll be using some new play aids that eliminates on table chits and can run four tanks on one sheet. We've already had new players running four at a time.

Wolfhag

"even in a square room with angles of 88 to 92 degrees…"

It's called TRIGONOMETRY – I used it hundreds of times calculating complex compound angles when designing skylight members in the Aluminum Architectural Skylight industry.

Just need a calculator with SIN, COS, TAN functions.

Nemonic: SOH CAH TOA
Sin=Opposite/Hypotenuese
Cos=Adjacent/Hypotenuese
Tangent=Opposite/Adjacent

I did the calculations for the compound angle armor values for the Panther that can fit on a 4x6 inch index card. It goes out to 70 degrees horizontal angle. The mantlet values are modified for cast armor. R = ricochet angle.

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I think they are pretty close. I have not had anyone else check them out or verify them yet. If this is workable it would be an easy way to quickly see if the lateral angle will really have an effect.

Wolfhag

I did the calculations for the compound angle armor values for the Panther that can fit on a 4x6 inch index card. It goes out to 70 degrees horizontal angle. The mantlet values are modified for cast armor. R = ricochet angle.

From a gaming perspective, that should be really useful provided your Panther is always sitting on a billiard table…

Tim -

"I just don't understand how it all works to combine the 4 angles together."

You solve for one triangle, say the slope with the projectile hitting the sloped armor straight on. Then when you find that actual "thickness" travelled through, use that as a side for the triangle using the new angle (the attitude towards the target (if not straight on) and use that "formula" again to solve for that NEW triangle to get to the compound angle resultant. Basically, a two-step process.

Think of the first solution as looking at the triangle as a profile from the horizontal view, you'll be solving for the hypotenuese – you'll know the original thickness of the material, and interpolate the proper angle opposite the 90deg – if you get what I'm saying.

Then, with that new linear distance, which will be the baseof the new triangle you are solving for, to find the new length or hypotenuese of that triangle. That would be the side of the triangle looking at it from the "plan" or "overhead" view to calculate the final triangle "side" that will give the linear distance you are looking for. Again you'll know the angle to the struck surface in "plan view" to give the angle of the triangle you are solving for now. Using the appropriate SOH CAH TOA "some old hags . . . " to solve for the HYP.

Really not complicated. You need SIN-COS charts or a calculater that can do SIN-COS-TAN's for the angles that are part of the formula.

Hopefully that made some sense if you were able to follow my description?!?

Cheers.