Tanks - Slopes, Turrets, Tracks, DR?

[Tallor]

I've seen dozens of entries on tanks thanks to the 3e WWII books, but I don't think I understand them on a technical or tactical level, especially the armor.

Correct me if I'm wrong, but here's how I assume the armor is distributed:

Front: 100%
Sides: 75%
Rear: 75-50%
Turret: 150%
Tracks: 50%

Something like that? Watching both real and fictional examples of tanks made me realize that the turret needs to be toughest, since it's the first part that pokes out from a hilltop or other defensive position. Does anyone have more precise numbers or better "tank theory" I could learn?

[Anthony]

Generally speaking, the tank's front and turret front will be armored to deal with contemporary tank and anti-tank weaponry, the rest will be armored to deal with machine guns and possibly light autocannons. Often this means as much as a factor of ten difference in armor levels between the front and everything else.

[Ulzgoroth]

There's not really a general tank theory. Your assumptions are wrong for most tanks, but not in any one consistent direction.

Tanks from late WWII on often have much more bias to front protection than you're predicting. A modern MBT is intended to resist a modern MBT cannon from the front. From any other angle it doesn't try to come anywhere close to that. Look at the T-72 at the back of High Tech: more than 6 times as much DR up front as on the side.

Some tanks focus more armor on the turret than the hull, but historically at least that wasn't always true. Look at the Pz. IV stats on HT238 - turret front armor is less than hull front armor.


I'm prone to over-detailing, but I don't think giving a single armor value for the entire front hull is actually a good idea. The most resistant part of the front armor is generally going to be the sloped upper surface (the glacis). If the tank is positioned so you have a shot at the lower angle, that's vastly more vulnerable. In an RPG with second-by-second resolution, I for one want to account for that sort of thing.


You mention sloping in the title, but don't get into it. It's probably best to treat sloped armor as having DR for its slope thickness: actual thickness / cos(angle). In reality, you can bypass sloping by having the right (usually elevated) firing position, or by some other gimmicks, but treating sloping as not working by default is going to make most modern armored vehicles look nonsensical, so it's not a good option.


Also, if it hasn't been mentioned to you, GURPS WWII takes its own special approach to vehicle stats that does not line up with GURPS 4e (and might not with other GURPS 3e, I'm not sure about that).

[Tallor]

Originally Posted by Ulzgoroth

...
Tanks from late WWII on often have much more bias to front protection than you're predicting. A modern MBT is intended to resist a modern MBT cannon from the front. From any other angle it doesn't try to come anywhere close to that. Look at the T-72 at the back of High Tech: more than 6 times as much DR up front as on the side.

Okay, so maybe a 6:1 Front:Side ratio would be appropriate?

Originally Posted by Ulzgoroth

Some tanks focus more armor on the turret than the hull, but historically at least that wasn't always true. Look at the Pz. IV stats on HT238 - turret front armor is less than hull front armor.

Just read that! So some tanks have tougher bodies than turrets... Personally I'd prefer a tougher turret since it's the higher point of the vehicle. I suppose it also depends on how much sloping is used...

Originally Posted by Ulzgoroth

I'm prone to over-detailing, but I don't think giving a single armor value for the entire front hull is actually a good idea. The most resistant part of the front armor is generally going to be the sloped upper surface (the glacis). If the tank is positioned so you have a shot at the lower angle, that's vastly more vulnerable. In an RPG with second-by-second resolution, I for one want to account for that sort of thing.

Actually that sounds like a cool idea. I imagine a sort of "Targeted Attack" system for hitting weak spots (like shot traps, for instance) would make aimed shots a lot more fun and involved!

Originally Posted by Ulzgoroth

You mention sloping in the title, but don't get into it. It's probably best to treat sloped armor as having DR for its slope thickness: actual thickness / cos(angle). In reality, you can bypass sloping by having the right (usually elevated) firing position, or by some other gimmicks, but treating sloping as not working by default is going to make most modern armored vehicles look nonsensical, so it's not a good option.

I apologize for not posting more about slopes! I imagine sloped armor (in relatively flat conditions) works similarly as it did in 3e, multiplying damage resistance. 30° = x1.5; 60° = x2.

Originally Posted by Ulzgoroth

Also, if it hasn't been mentioned to you, GURPS WWII takes its own special approach to vehicle stats that does not line up with GURPS 4e (and might not with other GURPS 3e, I'm not sure about that).

Oh but of course. I was just thinking about raw DR, which is quite similar in either edition.

[Ulzgoroth]

Originally Posted by Tallor

Okay, so maybe a 6:1 Front:Side ratio would be appropriate?

Well, for one tank it's somewhat okay, but I wouldn't bet on it even generalizing across modern MBTs. And earlier tanks, or light tanks that aren't designed to survive MBT hits, may have much lower ratios.

Originally Posted by Tallor

Just read that! So some tanks have tougher bodies than turrets... Personally I'd prefer a tougher turret since it's the higher point of the vehicle. I suppose it also depends on how much sloping is used...

Generally the glacis will have better sloping than the turret, because the turret needs to rise up enough to house the gun in a relatively limited space.

But, well, you're not alone in that preference. That T-72 follows it, for example.

Originally Posted by Tallor

Actually that sounds like a cool idea. I imagine a sort of "Targeted Attack" system for hitting weak spots (like shot traps, for instance) would make aimed shots a lot more fun and involved!

A lot of older (WWII, quite possibly also WWI) tanks have very non-uniform effective protection. Generally because they hadn't figured out how to make the front work with a single consistent slope. So you'd often have some really steeply angled bits which are actually relatively thin but basically impossible to penetrate due to the angle, and some bits that have little to no sloping and, despite being thicker, are much more vulnerable.

Modern design has much less of that, but there are still vulnerabilities if the angle is right.

I wrote up a detailed armor plan of an interwar/early WWII tank (The T-26) here. I'd be inclined to make up sub-location tables for each facing and attack penalties for called shots to the various bits. YMMV, practicality not guaranteed.

Originally Posted by Tallor

I apologize for not posting more about slopes! I imagine sloped armor (in relatively flat conditions) works similarly as it did in 3e, multiplying damage resistance. 30° = x1.5; 60° = x2.

Yeah, that's what you get from the formula I gave.

Originally Posted by Tallor

Oh but of course. I was just thinking about raw DR, which is quite similar in either edition.

But not necessarily in GURPS WWII.

This is all hearsay to me (see my tiny sig) but as I understand it GURPS WWII did not follow the same standards currently used for a number of things and DR was among them.

[Tallor]

In other words... there's no Grand Unified Tank Theory, and tanks are complicated machines with variations on both their base armor and the armor's slope.

But it would be cool if there were some guidelines for those wanting a ballpark idea of a tank.

[Ulzgoroth]

Originally Posted by Tallor

In other words... there's no Grand Unified Tank Theory, and tanks are complicated machines with variations on both their base armor and the armor's slope.

But it would be cool if there were some guidelines for those wanting a ballpark idea of a tank.

Well, we don't have a design system, so there's a lot of elements where you can't get rigor without either modeling a real tank or being a real tank engineer, but...

'Tank' is too broad to fit under one set of guidelines. I'm going to give two, but there could probably be more. Actual tanks can be expected to only approximately fit either set!

A main battle tank, heavy tank, or medium tank will typically have:

• The most powerful armor-piercing cannon that is practical to put into the turret. (WWII examples and especially early and pre-war examples often prioritize throwing powerful high explosive shells over armor piercing.)
• Enough front armor, between thickness and sloping, to resist an average damage roll from a comparable gun at range (Often it will penetrate at full damage but be easily stopped at 1/2D)
• Enough side and rear armor to resist a heavy machine gun or a grenade launcher and maybe a light autocannon. May also have armor skirts or reactive armor capable of resisting at least light HEAT warheads.
• Roof and bottom armor will stop shrapnel and rifle bullets at least, but are generally thinner than any other armor.
• Turret side and rear armor is generally weaker than front armor, but often stronger than hull side armor.
• At least a coaxial machinegun, often at least one additional machine gun.

A light armored combat vehicle, including light tanks, armored cars, and many armored personnel carriers will typically have:

• Enough armor on all sides to resist medium machine gun fire, usually including AP rounds. Heavier examples will resist heavy machine gun fire from some or all directions, and some may have front armor that resists light autocannon. Skirts, spaced armor, or reactive armor giving resistance to light HEAT warheads may be present.
• A light autocannon, automatic grenade launcher, or medium-velocity cannon for firing HE and HEAT rounds. Some light tanks have relatively small but powerful AP-firing cannons that can defeat heavier tank armor under favorable conditions. Some vehicles have an ATGM capability. Some vehicles, particularly pre-WWII, have only machine guns.
• Roof and bottom armor same guidance as above.
• Usually at least one machine gun.

For both types, crew is never less than 2 (driver and gunner), rarely less than 3 (driver, gunner, commander) and many examples have 4 (usually driver, gunner, commander, loader) or in WWII 5 (driver, gunner, commander, loader, radio operator/hull MG gunner). Some have more, mostly early tanks with multiple turrets or hull-mounted MGs.

[Anthony]

Originally Posted by Tallor

But it would be cool if there were some guidelines for those wanting a ballpark idea of a tank.

Broadly speaking, pick an attack that you think a tank should be able to withstand from a given angle, and give it enough DR to withstand the average damage of that attack. If you discover you can't actually handle that much weight, pick a different attack instead.

Typically that means small arms and light support weapons from the sides; what it means in terms of frontal armor depends a lot on what the tank is intended for.

[RyanW]

Originally Posted by Ulzgoroth

A light autocannon, automatic grenade launcher, or medium-velocity cannon for firing HE and HEAT rounds. Some light tanks have relatively small but powerful AP-firing cannons that can defeat heavier tank armor under favorable conditions. Some vehicles have an ATGM capability. Some vehicles, particularly pre-WWII, have only machine guns.

Note that light tanks can have pretty substantial main guns. The light tank has for a long time been marginalized, with wheeled vehicles and IFVs doing that kind of duty. However, there are light tanks out there with 105mm, 120mm, and 125mm main guns, often coming out of light vehicle families like the CV90 and ASCOD. The difference in a light tank with such a large gun and a tank destroyer is somewhat fuzzy, though.

Originally Posted by Ulzgoroth

For both types, crew is never less than 2 (driver and gunner), rarely less than 3 (driver, gunner, commander) and many examples have 4 (usually driver, gunner, commander, loader) or in WWII 5 (driver, gunner, commander, loader, radio operator/hull MG gunner). Some have more, mostly early tanks with multiple turrets or hull-mounted MGs.

Most modern tanks either have four crew members, or three and an autoloader. WWII was most typically 3+2 per main gun, minus one for each: no radio (no radio operator) or turret radio (radioman/commander duties combined), very light gun (gunner/loader duties combined), poor tank command doctrine (commander/gunner duties combined).

[weby]

Basically the armor levels of modern tanks get really complex.

A good example can be seen in Leopard-2A0-A4 armor protection estimation at: http://www.btvt.narod.ru/raznoe/leopard2/Leo2a4.htm

Specially the image: http://www.btvt.narod.ru/raznoe/leop...d-2A4-LOSy.jpg