Vehicles: 3E vs. 4E

[Fred Brackin]

Originally Posted by Ulzgoroth

That last seems clearly untrue, considering the extreme importance of armor sloping in the design of AFVs since about 1940. Treating all armor as unsloped will give you extremely wrong results - for instance, pretty much all late-WWII or later tanks frontal protection will be much weaker than designed and probably ineffective against the weapons it's supposed to stop.

This is where assigning armor DR by weight instead of thickness comes in. Putting in slope increases the surface area, and thus the weight of the armor. You get more DR.

[Rupert]

Originally Posted by Fred Brackin

This is where assigning armor DR by weight instead of thickness comes in. Putting in slope increases the surface area, and thus the weight of the armor. You get more DR.

Weight for weight, sloped armour gives you the same effective thickness as unsloped. It gives you an improved chance of deflecting shots if the armour has an extreme slope (hence the very long shallow slopes some modern AFVs have for the upper front/top front armour.

It also reduces the area of your top deck, so there's some slight weight savings there. However, it cuts into your internal volume, so that has to be made up for with extra height (and thus side armour) or length (and thus extra top and bottom armour and a heavier track system).

Note that the lower front glacis and the turret front of many modern tanks don't have as much slope as used to be fashionable, and almost nobody bothers with side or rear sloping other than a little on the turret. The exception being some Russian and Ukranian models, but that's actually the reactive armour boxes.

Also, if you rely on extreme slope, any time the slope is reduced even a small amount (such as when someone is firing on you from a higher elevation), the amount of protection you get is massively reduced. An example of this is the old BMP armoured personnel carrier/infantry fighting vehicle. It's upper hull front is extremely sloped and rather thin, and small arms penetrate it quite readily if fired from above, even if from a fair distance (and thus at only a small downward angle).

All this is why only some battleships had angled belts, and partly why the British didn't slope the fronts of the KGV class battleships' turrets or the armour on the Churchill tank. In the case of the tank they felt you'd get enough sloping from angling the hull, and the extra cost and loss of internal volume wasn't worth it. On the other hand, the Soviets angled the upper hull armour of the T-34 in all directions, so they clearly thought it worthwhile.

[Ulzgoroth]

Originally Posted by Fred Brackin

This is where assigning armor DR by weight instead of thickness comes in. Putting in slope increases the surface area, and thus the weight of the armor. You get more DR.

Which is pretty good if you're talking design systems, but almost never any use at all if you're talking statting real-world artifacts.

[Emerikol]

Originally Posted by Fred Brackin

This is where assigning armor DR by weight instead of thickness comes in. Putting in slope increases the surface area, and thus the weight of the armor. You get more DR.

I don't think slope armored tanks weigh more than non-slope armored tanks necessarily.

[Fred Brackin]

Originally Posted by Emerikol

I don't think slope armored tanks weigh more than non-slope armored tanks necessarily.

That's because of limits to suspension and engine power that the real world designers need to respect.

Slope armored tanks will mass more than a tank with equivalent volume but a more compact shape.

[Rupert]

Originally Posted by Fred Brackin

That's because of limits to suspension and engine power that the real world designers need to respect.

Slope armored tanks will mass more than a tank with equivalent volume but a more compact shape.

They'll also have a higher profile, in all likelihood.

[Ulzgoroth]

Originally Posted by Rupert

They'll also have a higher profile, in all likelihood.

Considering how much tank designers want to minimize height, that seems unlikely. Though we have no real examples of a non-slope-armored tank with remotely modern design understanding, so it's not an empirically accessible comparison.

[Emerikol]

Originally Posted by Ulzgoroth

Considering how much tank designers want to minimize height, that seems unlikely. Though we have no real examples of a non-slope-armored tank with remotely modern design understanding, so it's not an empirically accessible comparison.

The Tiger tank did not have sloped armor. There are examples of sloped and non-sloped armored vehicles.

I don't see height or weight being increased necessarily by sloped armor. Slope is supposed to give better protection for the same thickness of armor. It's the armor that weighs a lot. You can argue surface area but it's not really valid as the areas not directly related to taking the impact of a round were thin armor. It's why tanks were highly vulnerable to attack from above.

The Germans decided with the quality of their steel that nothing known could penetrate the Tiger when it was released. This was essentially true.

I imagine sloped armor requires better design and engineering as well and it may have been more time efficient to ship the tiger with super thick regular armor.


So my advice:
Find some tank to be your baseline for GURPS statistics. Then use the data from a game like Advanced Squad Leader to adjust all of the other tanks off that baseline. You ought to be able to lay your hands on some tank charts without having to buy the entire game. There are other good games out there as well so you could consider those as well. There is the Advanced Tobruk System. Various miniatures rules (which to be honest would be good enough for an rpg).

[Þorkell]

Originally Posted by Rupert

On the other hand, the Soviets angled the upper hull armour of the T-34 in all directions, so they clearly thought it worthwhile.

However it is interesting that the tank the Soviets designed to take over from the T-34 only had sloped armor on the front.

Originally Posted by Emerikol

The Tiger tank did not have sloped armor.

Sure it did. Granted it only sloped about 10° where it sloped.

[Ulzgoroth]

Originally Posted by Emerikol

The Tiger tank did not have sloped armor. There are examples of sloped and non-sloped armored vehicles.

While there are nitpicks with that claim, it did not have the glacis as a whole steeply sloped, no.

I stand by my statement, because I don't regard the Tiger as coming from a modern design understanding.