Re: [DS3] Dirtside Accelerator for Infantry

[forwarded for Oerjan Ohlson]

CS Renegade wrote:

>>Not if they want to hit moving targets at long range...
> 
>I wasn't implying a through-barrel missile system here,

Neither was I. It is the UNguided HEAT rounds which have problems
hitting
moving targets at long range, not the (guided or self-guiding) missiles.

>Moving targets? An evading target gets a secondary D8,

I'm talking about moving targets in the "real world" here, not moving
targets on the DS2 table. 

Due to their shape HEAT (and HESH, and any other rounds containing HE
charges) rounds slow down quickly once they've left the muzzle, giving
them
both relatively long flight times and high trajectories when fired
against
targets at long ranges. Long flight times greatly increases the risk
that
the target will make course and/or speed changes while the round is in
the
air (not necessarily in an attempt to dodge the round; it is more likely
that the course/speed change is made to avoid some minor obstacle in the
target vehicle's path), and a high trajectory means that any such
course/speed changes have a considerable (and detrimental) effect on the
hit
probability. 

KE rounds don't slow down nearly as much thanks to their much better
aerodynamic shapes, and therefore both arrive faster (minimizing the
risk
for any random target course/speed changes while the round is underway)
and
follow flatter trajectories (which reduces the effect of any
course/speed
changes the target happens to make anyway) - with a much greater
long-range
accuracy as the result.

In DS2 terms, you could fire unguided HEAT rounds from HVCs if you want
-
but if the target moved more than maybe half its BMF in its latest
Activation (not just "evasive" movement!) you should shift the FCS die
type
down 2 steps per extra range band instead of just 1. (If the target did
*not* move more than half its BMF in its latest Activation you use the
FCS
die specified in DS2 as usual.)

Contrary to Ryan's remark, this has everything to do with the round and
nothing to do with the fire control computer: the FCS can't compensate
for
any actions the target takes after the round has left the barrel, and it
is
the type of round, not the FCS, which determines both whether or not the
target has time to take any such actions at all and how big an impact
any
such actions have on the hit probability.

[snip] 

>>>But the distributions are still flat
>>
>>Sounds like you have a different definition of "flat" than I do, then.

> 
>If I draw one chit I get a variable set of outcomes based on 
>the relative frequency of chit values. If I draw two chits I 
>get a pyramid, skewed for the same reason.

The probabilities for the individual numerical values form a kind of a
skewed bell curve if you draw enough chits, that's true - but that's
irrelevant for the DS damage system, because you're not interested in
the
probabilities for the individual numerical values - only in the
probabilities for *groups* of such values.

Eg., let's say that you're drawing 3 chits against an Armour/4 vehicle
(and
ignore any Special chits for now in order to keep the example reasonably
simple <g>). The numerical results can be 0, 1, 2, 3, 4, 5, 6, 7, 8 or
9,
and each of these results has its own propability of occurring; together
they form a kind of skewed bell curve. You're entirely correct that a
single
pair of opposed dice can't replicate this distribution - *but it doesn't
have to do that*! When shooting at an Armour/4 target there's no point
in
tracking the separate probabilities for the 0, 1, 2 and 3 results,
because
they all have the same effect on the target (ie., none at all); all that
is
important is the *total* probability for getting any one of these four
results. Similarly it doesn't matter which of the 5, 6, 7, 8 or 9
results
you get, because any of them will destroy the target; so all you need to
know is the *total* probability for getting one of them.

IOW, instead of having 3n+1 numerical results where "n" is the number of
chits drawn, you only have *3* relevant statistical events no matter how
many chits you draw: these events are "total numerical value drawn is
less
than target Armour", "total numerical value drawn is equal to target
Armour", and "total numerical value drawn exceeds the target Armour".
Adding
in the special chits add a large number of further combinations to the
3n+1
"sub-events", but with the above "two different 'damage' results equals
one
kill" simplification there are still only 3 results *that are relevant
to
the game*: "no effect", "damage" (including specials), and "kill". 

IOW, the Accelerator doesn't *need* to re-create the entire bell-curve
distribution of all the possible numerical results (which is fortunate,
since it can't <g>); all it needs to do is to emulate the 3 relevant
probabilities for "no effect", "damage" and "destruction" - and that
*is*
possible for a single pair of opposed dice to do with the aid of the
Size
and Armour multipliers. If you shoot at a target with a different Armour
rating you'll get another set of 3 probabilities for the "no effect",
"damage" and "kill" events since the "sub-events" are grouped together
differently - but you still only have 3 probabilities to emulate, and
the
Accelerator handles that by changing the Armour multiplier. If you
change
the weapon size or type (ie., the number of chits drawn or their
validity)
you'll get yet other sets of 3 probabilities; the Accelerator handles
them
by changing the rating multipliers and/or the die types.

>Erm, I've just criticised the core FMA mechanic, haven't I? 

Nope, but you have given an excellent demonstration of the difference
between calculating statistics correctly and understanding what they
actually mean ;-)

>>...the validity bit on p.36 directly contradicts the validity table on

>>p.29, and when asked about it Mike Elliott stated that p.29 was 
>>correct and p.36 was wrong.
> 
>A bad dream is coming back to haunt me.

Yep.

>Still, there's no arguing with the author's opinion.

Of course there is - what do you think I'm doing on the playtest list
all
the time...? (Heck, according to the DS2 authors' opinion the HKP
concept
works, and I'm *definitely* arguing with that...)

However, if you're going to create an alternative game mechanic which
gives
roughly the same results as the original ones, you first need to know
for
certain exactly what it is the original mechanics do (which means
knowing
what author's opinion is, regardless of whether or not you agree with
it) -
otherwise you can't argue either for or against it :-/

>>Sounds as if you need to use a lot more terrain! Infantry doesn't like

>>wide-open plains; but if you play with terrain densities like those of

>>northern Europe (where you're lucky to have a LOS of more than 1 mile,

>>and the average LOS is IIRC about half that) they're a lot more
useful.
> 
>Using a cm scale for DS2 we have an area of 120x182 available, with 
>games played sometimes down and sometimes across the table. Open 
>areas between obstacles are often in the region of 50-80cm,

In other words you have longer average lines of sight than the Coalition
had
in the flattest desert areas during Desert Storm!

In contrast representing an average north-European battlefield in the
same
cm scale would give you open areas between obstacles in the *5-20* cm
range,
with longer lines of sight being very rare. As Ryan suggested, try using
a
lot more small LOS-blocking terrain features (small hills, copses,
isolated
houses and the like, all of which block LOS but don't hinder movement
much)
- and see what differences that makes to tactics and weapon
effectiveness.

>>(Note that DS2's description of HKPs is complete bunk - the weapons 
>>described by that blurb would find it extremely difficult to get up to

>>even HVC performance...)
> 
>Doesn't DS2's HKP concept presume far higher barrel pressures?

Sure does; it also assumes smaller calibres and longer barrels. Each of
these assumptions has its own problems, and together they are outright
disastrous:

* In any propellant-powered gun, the force on the projectile (incl.
sabot)
is equal to the barrel cross-section area times the propellant gas (or
plasma) pressure. The barrel cross-section area is proportional to the
square of the calibre; eg. for a round barrel cross-section the area is
equal to calibre^2*Pi/4 (plus a little extra for the rifling if there is
any). This means that a smaller-calibre barrel either needs higher
pressure
or a longer barrel, or both, just to get the SAME muzzle energy as a
larger-calibre barrel would give - and the pressure and/or length
increases
necessary for this are quite large: eg., if you decrease the calibre by
one-third you need to increase the maximum pressure and/or barrel length
by
a total factor of 2.25 just to get back to the *original*
(large-calibre)
muzzle energy. If you want to beat the large-barrel performance (ie.,
achieve an even *higher* muzzle energy), you need even higher pressures
and/or longer barrels.

* Increasing the length of the barrel significantly is impractical for
two
main reasons: vehicle manoeuvrability and barrel droop. Today's MBT gun
barrels are around 5-6 meters long, and they already cause problems when
the
tank is manoeuvring in restricted spaces (eg. roads lined with lamp
posts or
road signs) since it is tricky to avoid banging the barrel into
obstacles.
Imagine what'll happen if you increase the barrel length by another
several
meters! (...the Tiger scene in "Kelly's Heroes" springs to mind...)
Barrel
droop is less intuitive: gun barrels are always slightly bent by
gravity,
but when they're fired they straighten out temporarily and can also
sometimes start wobbling a bit. Of course this movement isn't very
large;
but it is large enough to impart a small transverse velocity component
to
the round as it goes down the barrel, and since this transverse movement
is
slightly random the FCS can't compensate fully for it - which hurts the
gun's accuracy. The longer the barrel is, the more it'll droop and the
larger a transverse velocity it'll impart to the round, and therefore
the
greater the accuracy problems become.

* Increasing the pressure also causes problems, because it means that
you
need to increase the thickness of the barrel walls to prevent the barrel
from bursting. If you only want your low-calibre, high-pressure HKP to
*match* the HVC performance, you'll need to increase the thickness of
the
barrel walls and/or length so much that the HKP barrel will weigh at
least
as much  as the HVC barrel - and often more, because the pressure
generally
drops slower in the narrower HKP barrel so it needs to be thicker for a
larger proportion of its length than the HVC barrel does. And this was
just
to *match* the HVC performance; if you want your HKP to *exceed* the HVC
performance you need a longer and/or even thicker-walled barrel (able to
withstand even higher pressures), resulting in a weapon which is
significantly heavier than the corresponding HVC.

All in all, for a *given* weapon performance (projectile weight and
velocity) the HKP as described in DS2 will be at least as clumsy, heavy
and
expensive as the HVC, and quite likely worse in all three respects. If
the
HKP is to perform *better* than the HVC, ie. fire heavier projectiles
and/or
fire its projectiles at a higher velocity, it will be even heavier,
clumsier
and more expensive than the corresponding HVC - and if in addition it is
longer, it will also be both harder to manoeuvre with and less accurate
than
the HVC.

Makes the HKPs sound like a really good deal, doesn't it?

>As to why this might be better than sticking with 
>the HVC design, the weapon would be smaller

Nope. See above.

>and the ammunition would take up less space and be less volatile. 

A bit less space for the rounds themselves due to the smaller sabots,
but
not for the propellant.

>(The exotic HKP propellants might even be fed from a tank 
> rather than loaded as a cartridge or charge.)

The HVCs are already described as using liquid propellants, so no
difference
there.

>Do modern MBTs still have hand-loaded rounds, and if so, how close to
the 
>limits of manual handling are they?

Most do and fairly close, respectively.

>Wouldn't MBT design and logistics both be easier if the round was just
the 
>penetrator and a half-litre of skunkworks moonshine?

Nope; Ryan's comments are right on target here. In addition liquid
propellants requires a lot of sealed tubing to get from the storage
tanks
into the guns (unless of course you put it in cartridges similar to how
today's solid propellant is handled), and loading the propellant
separately
from the projectile increases the loading time since there are two
separate
things which must be loaded in sequence instead of just one single
cartridge.

>>>Possibly I'm just prejudiced by the number of models available in the

>>>market with large-calibre guns looking for a role,
> 
>>Calibre only refers to the inner diameter of the barrel, and whereas 
>>an HVC barrel is essentially just a steel tube the MDC barrel is lined

>>with a lot of equipment - magnets, electrical circuits, cooling gear 
>>etc. - which is likely to make it much thicker (i.e., with a larger 
>>*outer* diameter) than a HVC or RFAC of the same calibre.
> 
>True, but I like the idea of a gun that can fire a variety of 
>different rounds

But that has nothing whatsoever to do with what the *models* look like,
and
it was the visual appearance of the models you used as an argument
above.
Besides, virtually all gun barrels are over-size on DS2-scale models
since
they'd be way too thin to cast or use in gaming otherwise - eg., even an
152mm "HVC" gun barrel would be a mere 0.6mm thick if it were modelled
true
to scale, and a 25mm autocannon barrel in 1/300 scale would be about
0.05mm
thick.

>>>and I'm certainly not sticking HVC on a hovertank.
> 
>>Because of the recoil? Then you shouldn't put big MDCs on them either 
>>- MDCs throw similarly-sized projectiles at significantly higher 
>>velocities, so their recoil is even worse than the HVCs'.
> 
> As the HKP is a development of the HVC, 

I'd rather describe it as a *degradation* of the HVC :-/

>I'd view ground-effect and then gravitic mobility as technological 
>steps forward from wheeled and track-laying systems. 

Gravitic mobility yes, but hovercraft have been with us for decades
already
- without even threatening to replace wheels and track-layers except in
a
small number of specialized niches...

>They aren't parallel developments 

Exactly - they *aren't* parallel developments. And since they aren't,
there's no reason whatever why would a force able to build *hovercraft*
must
necessarily be able to build *weapons* better than HVCs as well.

>and a force will only utilise an earlier system if it is unable to buy
/
build the 
>latest equipment. 

This is just plain wrong; most forces will utilise an earlier system
even if
it could afford later ones as long as it earlier system is demonstrably
more
effective than the later. As for arming hovercraft, putting *any*
large-recoil weapons on a hovercraft causes problems as soon as you
attempt
to fire them - there's a very good reason why today's military
hovercraft
are armed with missiles, machineguns  and light autocannon (ie.,
low-recoil
weapons) instead of with large-calibre tank or ship guns.

>I've no objection to APSW (or similar weapons) being shifted 
>to very low effectiveness by the imposition of cover, but 
>they should be highly effective against infantry advancing 
>over open ground.

*ALL* weapons should be highly effective against infantry advancing over
open ground. In DS2 however *ALL* weapons are massively degraded against
*ALL* types of targets by the simple fact that the weapons get to fire
only
one shot (or burst) during an entire 15-minute game turn - whereas
real-world weapons could fire dozens, hundreds or even thousands of
shots
during a 15-minute firefight.

>Thanks for sorting out my understanding of these weapons; 
>it's been too long since I've looked at the relevant publications.
> 
>I would expect a cannister round that burst on leaving a 
>contemporary HVC to have a very limited range and thus only 
>be useful as a final defensive munition.

Muzzle-bursting canister rounds have a lethal range against unarmoured
infantry of 100-600 meters, depending on the size and type of gun that
fires
it and the terrain. (And, as Ryan said the muzzle-bursting and
long-range
canister rounds are often the same type fired at different range
settings.)

>By contrast, a sabot-riding bundle of flechette darts leaving 
>a DS2 MDC would be travelling _very_ quickly

...when it leaves the muzzle. The problem is that they would also *slow
down* very quickly as soon as they leave the sabot, due to the large air
resistance the yawing caused by the separation from the sabot gives.

>, and given the same cross-section / weight ratio of a full-sized rod
the 
>darts could be expected to travel just as far.

"Given the same...", sure. But they don't, because unless you use a much
denser material in the flechettes than you do in the full-sized rods
(which
is highly unlikely, since you're already using as dense a material as
you
can in your full-sized rods) the only way you can give the flechettes
the
same areal density (ie., weight/cross-section ratio) as the full-sized
rod
is to make them the same LENGTH as the full-sized rod - and if you make
your
flechettes that long, you'll also need to make them as *thick* as the
full-sized rod to allow them to survive being fired without bending or
breaking up in flight! 'Course, if the flechettes are both the same
length
and the same thickness as the full-sized rods, then they are full-sized
rods
themselves and not flechettes at all...

In short, your flechettes *won't* have the same areal density as the
full-sized rods. Unless they're actual full-sized rods they'll have a
lower
areal density, which means that even without the yawing caused by the
sabot
separation they'll be far worse affected by the air resistance.

>So if my high-speed flechette isn't sufficient, what 
>vehicular weapon could be devised to defeat power armour? 

Heavy bullets - 0.5" and up. Larger HE grenades should work OK too -
25-40
mm HE (including ICM) are too wimpy unless they score direct hits, but
once
the grenade calibre is above 80mm or so the shrapnel should be able to
get
through the body armour. Then of course you have white-hot plasma,
high-energy laser pulses, or plain old flame-throwers to burn the suit's
sensors out and boil the guy inside alive... in fact pretty much
everything
*else* in the DS2 arsenal would realistically work better against PA
than
flechettes do.

>Given the above table, all we have at the moment are APSWs 
>and other PA, and I'm a bit sceptical about anything less 
>than an HMG ("class 0.5") standing any chance at all.

Today's 7.62 AP bullets go through approx. 15mm RHA (standard, fairly
soft
reference steel plate) or around 40mm of high-grade aluminium armour...
it
all depends on how much you can armour your PA suits before they sink
into
the ground :-/

>The APSW doesn't appear to be described anywhere other than on pg 
>11, but I have always taken it to include all the smaller-calibre MGs
too.

If you look at the effects the APSWs have in the game rather than at
their
PSB description, the *only* thing the APSW mechanic covers are the
medium-calibre MGs - it is way too weak to represent today's HMGs, AGLs
and
similarly-sized weapons at all (which is why I want to introduce a
"size/0.5" class to represent them!). The smallest DS2 MGs,
corresponding to
today's 5.56 LMGs and SAWs, are already included in the Line infantry's
"Rifle" fire stats.

>>DS2 PA already *has* a choice of weapons: [snip]
> 
>I'd view powered armour as being short-changed in all of those roles, 

Short-changed compared to *what*? Not compared to any other units in the
game, that's for sure - PA already have the best anti-infantry weapons
in
the game, some of the best armours in the game, the best Close Assault
capability in the game (all enemies gets an extra Confidence penalty for
being CA:ed by PA); and while they don't have any particularly
impressive
anti-tank capability they're just too *small* to carry any direct-fire
anti-vehicle guns larger than what could be represented by the IAVR or
GMS
mechanics since such guns are as big as an entire entire PA suit anyway!
(One PA suit takes up 2 capacity points when carried in a vehicle; an
arm-mounted Size/1 weapon on a Walker also takes up 2 capacity points.)
If
you want such heavy weapons on your suits, the suits will be big enough
to
rate as vehicles - so use the "Infantry Walker" mechanics to represent
them,
not the "PA" mechanics!

Regards,

Oerjan
oerjan.ohlson@telia.com

"Life is like a sewer.
 What you get out of it, depends on what you put into it."
-Hen3ry