Explosive Reaction Armor

[General Lee]

I'm in litle trouble here.
Gurps High Tech 4Egive stats for guided missiles with MS-warheads, like the Javelin, Milan 3 and also modern RPG-7 versions to counter, especially, explosive reaction armor (ERA).

I know beforehand that the first "stage", warhead, is to disrupt the ERA so the second "stage" could achieve the armor more efficiently and do more damage.

But I don't see anywhere, how to represent ERA armor in a vehicle. There's anything in vehicles 4E for that? Probably, there's ERA armor to fit in 3E campaigns, but I'm not acquainted with it. So help me if you can. I don't like much screaming an result of an attack without some knowledge of how the real thing is emulated by the system.

Thanks in advance.

General Lee

[Fred Brackin]

Originally Posted by General Lee

But I don't see anywhere, how to represent ERA armor in a vehicle. There's anything in vehicles 4E for that?

The 4e Vehicles book (to be a pdf known as VDS or Vehicle Design System AFAIK) is not yet published ans probably won't be for a significant period of time.

It's hard to say exactly how to handle this. 3e did it a couple of different ways over a period of years.

In HT now it basically amounts to "add the two attacks together". The UT equivalent is basically an extra layer of armor that's more effective against HEAT.

I'd probably end up saying that reactive armor should treated as in UT and multi-stage warheading is really just a technique for improving HEAT penetration more than a different sort of weapon in terms of game mechanics.

[SuedodeuS]

For most purposes, you could probably just say that reactive armor defeats shaped-charge warheads outright - unless it's something like MS-HEAT, where it only defeats the first charge. Of course, it does explode to do so, and one of the problems with it is that it therefore threatens nearby infantry. I suspect the explosion is comparable to the secondary effect of a HEDP warhead. The biggest HEDP warhead in HT is the Carl Gustaf M2, with 6dx3 [4d+1] as its secondary. This is perhaps a bit much, so we'll go with the HEC M72A2 LAW, with 6dx2 [3d+1]. With this explosive, it's capable of stopping a HEAT round dead - although nearby infantry are going to be in trouble!

For a more advanced look than just "defeats HEAT outright," we'll look at some of the HEAT rounds. The largest "boom" is the secondary effect of the Javelin (which is 6dx11(10)). Just enough to stop this for a modern MBT with ERA might be a good baseline. This requires a total DR of 3610. The MBT from HT has DR 1155. Thus, the ERA must add somewhere around 2500 DR. Using the relationship Reactive Armor Paste (from UT) has, this means the ERA grants 250 DR, multiplied by 10 against shaped charges.

So, a "layer" of ERA does 6dx2 [3d+1] cr ex when activated. It grants 250 DR, multiplied by 10 against shaped charges. It only works against the first stage of MS-HEAT (although multiple layers that activate independently might be possible). It may or may not work against kinetic penetrators - if it does, you'll generally need more than one layer (as DR is not multiplied by 10 in this case). How much does it weigh? I have no clue.

[General Lee]

Originally Posted by Fred Brackin

The 4e Vehicles book (to be a pdf known as VDS or Vehicle Design System AFAIK) is not yet published ans probably won't be for a significant period of time.

I regret that. The only major handicap of the system in my opinion. I know that there are ways to circumvent this, but It's not the best way. i just want to try pry some information of the upcoming new vehicle system.

Originally Posted by Fred Brackin

In HT now it basically amounts to "add the two attacks together".

If there is no ERA.

Originally Posted by Fred Brackin

The UT equivalent is basically an extra layer of armor that's more effective against HEAT.

It's the same as spaced or laminated armor.

Originally Posted by Fred Brackin

I'd probably end up saying that reactive armor should treated as in UT ...

The only mention in Gurps UT 4E of reaction armor is in page 189 as Reaction Armor Paste. Despite it works as ERA ,I feel that lacks something...maybe a "special effect" instead additional DR. For example, drop armor divisor of the first charge, or the only warhead, rather than add DR200+.

Originally Posted by Fred Brackin

and multi-stage warheading is really just a technique for improving HEAT penetration more than a different sort of weapon in terms of game mechanics.

I concur with you. MS-warheads are not a new type of weapon, but an improved HEAT warhead. I just use them in my post because there is a purpose in use MS-warheads that it's not covered by the system accordingly.
But it could be a misunderstanding of my part.

[General Lee]

Originally Posted by SuedodeuS

For most purposes, you could probably just say that reactive armor defeats shaped-charge warheads outright - unless it's something like MS-HEAT, where it only defeats the first charge. Of course, it does explode to do so, and one of the problems with it is that it therefore threatens nearby infantry. I suspect the explosion is comparable to the secondary effect of a HEDP warhead. The biggest HEDP warhead in HT is the Carl Gustaf M2, with 6dx3 [4d+1] as its secondary. This is perhaps a bit much, so we'll go with the HEC M72A2 LAW, with 6dx2 [3d+1]. With this explosive, it's capable of stopping a HEAT round dead - although nearby infantry are going to be in trouble!

For a more advanced look than just "defeats HEAT outright," we'll look at some of the HEAT rounds. The largest "boom" is the secondary effect of the Javelin (which is 6dx11(10)). Just enough to stop this for a modern MBT with ERA might be a good baseline. This requires a total DR of 3610. The MBT from HT has DR 1155. Thus, the ERA must add somewhere around 2500 DR. Using the relationship Reactive Armor Paste (from UT) has, this means the ERA grants 250 DR, multiplied by 10 against shaped charges.

So, a "layer" of ERA does 6dx2 [3d+1] cr ex when activated. It grants 250 DR, multiplied by 10 against shaped charges. It only works against the first stage of MS-HEAT (although multiple layers that activate independently might be possible). It may or may not work against kinetic penetrators - if it does, you'll generally need more than one layer (as DR is not multiplied by 10 in this case). How much does it weigh? I have no clue.

Bingo!
Thanks a lot.

I, as posted above, reckon that the first stage of an MS-HEAT is defeated outright by ERA, but it still could do damage, because despite the hot jet it's not formed , the warhead still explodes adding peril to infantry or other targets less protected near the vehicle with ERA.

For that I suggest dropping the armor divisor.

If it's the only ERA layer, then the second stage would function properly, because the second stage is almost all the time bigger than the first.

I think DR250 to ERA a litle bit overpowered if you would multiply it by 10.

I see two alternatives: or to drop, as I said, the armor divisor; or to multiply by 10 the DR of ERA.

I'm enjoying the discussion here guys.

[SuedodeuS]

Overpowered or not, DR 250 multiplied by 10 is what you need for an MBT to defeat the secondary charge of the Javelin. If modern ERA is insufficient to stop it, I fail to see a reason to include the first charge (which blows away the ERA).

That said, you could state that it simply has sufficient levels of Hardened against shaped charges to negate the armor divisor. It's the same effect, really. Regardless, DR 250 is what's applied against kinetic penetrators... provided the ERA is designed to explode when struck by such!

[General Lee]

Originally Posted by SuedodeuS

Overpowered or not, DR 250 multiplied by 10 is what you need for an MBT to defeat the secondary charge of the Javelin. If modern ERA is insufficient to stop it, I fail to see a reason to include the first charge (which blows away the ERA).

That said, you could state that it simply has sufficient levels of Hardened against shaped charges to negate the armor divisor. It's the same effect, really. Regardless, DR 250 is what's applied against kinetic penetrators... provided the ERA is designed to explode when struck by such!

Right, enligthening enough.

[Fred Brackin]

Originally Posted by General Lee

It's the same as spaced or laminated armor.

Not exactly but probably close enough.

The way you've been discussing doing this with other people in this thread is very like the earliest treatments of Reactive Armor in 3e but from discussions involving Hans and others I believe it was decided that it was not truly accurate.

From those discussions I believe that a Reactive Armor plate of a certain plate can only disrupt a HEAT jet of a certain size. Ones that are too big are only partly affected. I think this is what triggered the simple "Extra DR" solution.

[General Lee]

Originally Posted by Fred Brackin

Not exactly but probably close enough.

The way you've been discussing doing this with other people in this thread is very like the earliest treatments of Reactive Armor in 3e but from discussions involving Hans and others I believe it was decided that it was not truly accurate.

From those discussions I believe that a Reactive Armor plate of a certain plate can only disrupt a HEAT jet of a certain size. Ones that are too big are only partly affected. I think this is what triggered the simple "Extra DR" solution.

I don't get it right, could you explain, I would apreciate a lot. I ain't seeing the nuances here.

[Fred Brackin]

Originally Posted by General Lee

I don't get it right, could you explain, I would apreciate a lot. I ain't seeing the nuances here.

The argument goes something like "A large HEAT such as found on a Maverick ATGM attacks a tank with Reactive Armor. The Reactive Armor activates but only partly disrupts the penetrating jet of ultra-fast liquid metal and pentration of the tank's armor occurs anyway."

"If you model Reactive Armor simply as negating the (10) armor divisor the result would be no penetration. This fails the Reality Check. Reactive armor will not defeat all HEAT attacks regardless of size. Some very large ones will penetrate anyway"

"If you model Reactive Armor as simply providing _some_ extra DR it will model both the effects of small HEAT and large HEAT."