Facing was: Well, too interesting

[quoted original message omitted]

> --- "K.H.Ranitzsch" <KH.Ranitzsch@t-online.de> wrote:

> ----- Original Message -----

*SNIP*

> I know no set of war games rules that explicitly

A couple of ideas:

1. You can always PSB it that the armor is more rounded in the future, or the
armor rating for any
side is an average of head-on and glancing, and just
ignore the issue. 2. If you want to simulate it, there are a couple of ways.
I'm not sure if I'd advocate them for the basic rules, but they might be
useful HR's: 2a. Any To Hit roll that rolls the minimum needed to hit, scores
only a glancing shot, and suffers either a damage class penalty or a 1 range
band validity penalty. 2b. roll a Dx for every hit. If the result is a 1, then
it's a glancing hit.

> KHR wrote:

> At least for WWII tanks, the optimum orientation was NOT facing the

Yep - because many WW2 tanks, particularly German ones, had poorly
sloped
(or even vertical), flat (ie., non-curved) armour plates and a
relatively even distribution of armour thickness around the hull. By turning
the diagonal towards the enemy you created a "sloped armour" effect increasing
the effective armour thickness, but you often did this at the cost of
increasing the target area displayed to the enemy... and, of course, at the
cost of having to put relatively heavy armour on the sides of your vehicle as
well as on the front (since any angle big enough to give a significant boost
to your frontal armour will also give a significant risk of
projectiles hitting the side armour *not* glancing off). Sloped/curved
armours give similar effects even when the vehicle is facing straight towards
the enemy, in addition to allowing the sides to be lighter armoured and
presenting a smaller target area to the enemy. ('Course, DS2 doesn't

allow vehicles to have different Signatures from different aspects - and

for playability reasons I'm not particularly inclined to make DS3 do it
either :-/ )

But your main point is very good: for many vehicles, DS2's way of determining
the angle of attack in the diagram on p.32 isn't very
appropriate - and for some models, eg. GZG's DSM-116 Poruzh with its
wedge-shaped hull, it can be pretty difficult to apply the p.32 diagram
anyway. I'd prefer to use simple 90-degree arcs instead, mainly because
it is simpler to use in play but also because it takes some of the effects of
glancing fire on the forward side armour (which in reality is effectively part
of the frontal armour anyway) into account.

Later,

From: "Oerjan Ohlson" <oerjan.ohlson@telia.com>

> KHR wrote:

> But your main point is very good: for many vehicles, DS2's way of

The only set of rules that I know of that attempted to take into account
facing and slope to the nth degree was Tractics, by Guidon Games, which later
became Tactical Studies Rules, and thence TSR.
http://www.theminiaturespage.com/rules/ww2/tractics.html

The chances though were all wrong : the optimum tank-killer was a
quadruple
50 cal MG on a half-track. With 24 shots per turn, the odds were that at
least one would hit a turret ring, vision slot, track pin etc etc causing a
mobility or firepower kill.

OO is the expert on exterior ballistics: but I've done a little study on
effective armour thickness of vehicles. The problem is that to say that
"Vehicle X has thickness Y mm at a slope of Z degrees" is a gross
simplification. Depending upon the angle of incidence of the vehicle, the type
of terrain it's going through, the range and the type of ammunition being
fired, you can get anything from 100cm at 85 degrees through to 2cm at 0
degrees (ie episcope etc).

Hit one place, you have to go through metres of armour - hit 2 cm away,
and you can jam a turret ring with even a rifle bullet. And a rifle bullet
that hits the open muzzle of a tank gun while the breech is open can KO
anything.

What tank designers do is play the percentages: they skimp on armour in areas
normally covered by terrain, they skimp on sides, top and rear. Normal AP
shells that hit the top of tanks do so at extreme angles of incidence, over
85 degrees. Long-rod penetrators basically don't even do that. If you
divide
the silhouette of a tank into 100 eqaul-sized areas, you may find
something
like 5 having 2 metres+ armour, 5 having 1.5 metres, 85 having 1 metre,
4 having 5cm, and 1 having 2cm.

And even that's a simplification: for example, a relatively slow-moving
round hitting a sloped plate will tend to rotate and penetrate at nearly
normal
incidence, due to drag. The there's shots shattering vs face-hardened
plate,
ballistic caps to prevent this, and then you have long-rod penetrators
which are best described as fluids hitting a fluid wall, and HEAT rounds which
if they're exactly right have metres of penetration, but slightly wrong and
it's at best 20 cm. (No, they're not plasma jets, the copper lining becomes a
slug
that moves at about 5 km/sec, though I'm sure OO can give more details).

I've done some modelling in insanely intricate detail of shells of various
types hitting tanks. But a reasonable approximation, within cooie
of the most detailed and complicated simulation, is to just roll a D6 -
take 80% of the tank's notional armour, and add 10% per score, so result
is 90%-150%.
This doesn't work for all vehicles, or all angles, but close enough for the
majority. There's always oddities like the Archer, or even
up-armoured
Pz IIIJs, where half the time the effective armour is about 4 cm, the other
it's more like 10. Always remember though that crews often weld tracks etc
on vulnerable points, but that externally-carried gear can catch fire
even from 20mm. Penetration does not equal KO, you can penetrate without KO,

Adding a few comments to Alan Brain's post:

> OO is the expert on exterior ballistics :

More *in*terior (propellant charges, rocket engines etc.) than exterior,

though I do both. The terminal ballistics set some of the parameters I have
to play with so I need to stay reasonably up-to-date with them too, but
they're not my particular area at work.

> but I've done a little study on effective armour thickness of vehicles.

> The problem is that to say that "Vehicle X has thickness Y mm at a

> 100cm at 85 degrees through to 2cm at 0 degrees (ie episcope etc).

Some vehicles are even more extreme in this respect; eg. the upper glacis
plate on the Abrams is (all numbers IIRC, but in the right neighbourhood

:-/ ) about 2" thick... but since it is mounted at an 85-degree slope
from the vertical, giving it an effective *horisontal* thickness of ~24". (Not
to mention that the odds of hitting the nearly horisontal upper glacis instead
of the *much* better protected turret front when shooting at an Abrams at your
own level of altitude aren't very good, of course; OTOH, when shooting at it
from above the upper glacis is a rather bigger target than the turret front.)

> Hit one place, you have to go through metres of armour - hit 2 cm away,

Very much so, even though the odds for this happening are quite low. Which is
why things like DS2's "BOOM" chits are mostly a good idea (though the

exact number of times they should crop up can be discussed <g>), and also why
I don't always have too much sympathy with those who complain about SG2
(or DS-FMA)-style level-5 armour (rolling D12x5 for its armour score)
being
damaged by a Size/1 Impact D6 weapon if the weapon happens to roll a "6"

and the armour die rolls an "1". It does happen occasionally... not very

often, but it happens.

> What tank designers do is play the percentages: they skimp on armour in

And of course the game designers play (or at least *should* play; not all do)
the percentages the other way: when firing at the above vehicle a freak lucky
penetration roll from a weak weapon represents hitting one of those 6
weak areas, while a very poor one from a heavy tank-killer could
represent hitting one of the exceptionally tough areas (or a faulty HEAT
round, or

any other of a myriad things that could've happened). Merely looking at
nominal armour values and saying that "this weapon has an armour penetration
of 500 mm RHA, so it can never hurt that vehicle which has armour equal to
600mm RHA" is quite misleading.

> [...] HEAT rounds which if they're exactly right have metres of

The slug Alan mentions here causes at best the after-armour effects,
though. Most of the actual armour penetration is done by the front part of the
jet (while the jet actually consists of solid metal under extremely high
tensions it behaves as a fluid, so we call it a "jet" nevertheless
-
but this does *not* turn it into a plasma... <g>) which tends to move at

10+ km/sec instead in modern HEAT warheads. Not that is in any way
relevant for how to model the things in a game, of course <g>

> Have a look at the WRG rules for AP - they took actual combat results,

Yep. The WRG AP rules *seem* overly simplistic, so many players spurned
them because "rules this simple can't possibly be *real*istic"... :-(

Later,