SV: [SG2] vehicle weapons vs. infantry

Barclay, Tom wrote:

>Oerjan responded to Brian? perhaps:
> 
>>You may apply whatever PSB you like. They may throw slivers no
>>larger than a needle, using the kinetic energy focused on an
>>extremely small point to penetrate armor.
> 
>Unfortunately armour penetration isn't as simple as increasing the
>kinetic energy :-( Slivers as small as needles simply don't have
enough
>material to do more than damage the outer layer of a
>composite armour, even if you can give them the structural integrity
>they need to not burn up during the flight or shatter on impact. 
> 
> --------------------------
>I take it then, as makes sense, that there is a maximum amount of
>energy you can usefully impart to a projectile.

Depends on how you define "usefully". For some reason most soldiers
seem to consider increased range and accuracy as "useful" as well as
improved penetration <g> 

But yes, if you only talk about penetration, then for a given
projectile (shape and mass) there's a maximum amount of "useful" energy
you can put into it.

>I know the point of some penetrators is to get a good length/cross
>section so they can pack a lot of mass behind one small impact area -
>thus giving a good whack to the target. 

All penetrators need a high length/diameter (L/D) ratio to defeat heavy
armour, yes - eg. modern APFSDS rounds have L/D ratios in the 20-25
range, and shaped-charge jets can reach far higher ratios since they
don't have the same problems with structural integrity. In post where I
discussed the size of MDC/5 long-rods I assumed L/D ratios in the 35-50
range, which requries quite impressive advances in metallurgy etc.
compared to what we can do today.

>I'd also think, at some point, you run into the issue of the round
>sublimating to molten metal or gas because it hits so hard... hence it
>can't liberate any more KE into the target (though hot gas or
>metal might be uncool for the target...). Is this what happens?

Not exactly. The round "liquifies" on impact (I guess you can call it
"melting", but that'll have the solid state physicists screaming at you
- I won't, since I'm into fluid dynamics, not solids <g>), but that's a
feature rather than a bug.

Very simplified, what happens is that the armour material and the
penetrator both "liquify" at the point of impact, and the "liquid"
material is
transported backwards ("splashes") along the sides of the hole and
gives room for the rest of the projectile to proceed inwards. The
longer the penetrator is, the deeper it gets before all of it has been
"used up". It's similar to cutting through sandstone with a
high-pressure water jet, except that you have a very limited volume of
water (and that the armour is more solid than sandstone :-/).

If the material (armour and penetrator both) does not liquify, the
projectile needs to push the armour aside. If the armour is thin it can
buckle and "peel away", if it is soft and squishy (like flesh) it can
be compressed, but if it is thick and non-compressible the only way to
push it is into the rest of the armour... which won't yield easily. If
this happens, the penetrator often won't get through.

However, for high enough projectile velocities air friction gets so
high
that the projectile starts melting or abrading *before it even reaches
the
target*. If the projectile is a small needle the entire projectile may
simply disappear; for fin-stabilized projectiles the fins take damage
which destroys the stability of the round, and thus reduces the range
and accuracy somewhat and the penetration massively. This isn't a good
thing at all :-/

>Relatedly, you mentioned that D8 might be a bit low for beehive
>rounds. I'd guess so.... 

Yep :-/ Though maybe not, given how many of the SGII ranges have
partial or full body armour - some more thoughts on this further below.

>I think that all vehicle weapons may have some anti-infantry mode.
>Let's review how these might work briefly:
> 
>RFAC - small ones are like the Vulcan - anyone who has seen one
>deployed vs. infantry will know exactly how nightmarish that is. 

At least small ones *could be* like the Vulcan. Depends a bit on the
ammo supply though - a Vulcan or similar weapon eats *huge* volumes of
ammo even for a short burst.

>Large ones undoubtedly can fire proximity fused rounds with laser
>range finders thus making life bad for the infantry. 

Yep. Well, small ones can do this too - all the way down to the 25mm
grenades the USAR's OICW (currently under development) is supposed to
fire. Don't know how far that project has come, though.

>HVC - Well, I wouldn't want to get hit by one of these as an infantry
>guy. It'd kill you I'd think. But it would only affect one man in the
squad
>if that. Hard to hit with. But maybe there are HVC rounds that
actually >are anti-infantry in design that can fragment with some sort
of fusing >(sensor triggered or pre-set distance).

There are both timer/revolution counter- and sensor-fused HE rounds for
MBT main guns available today, so I see no reason why they wouldn't be
available in the future. Timer-fused ones have been in service for many
years, though I'm not sure if any army has accepted sensor-fused ones
yet. 

(Maybe IDF has - at least one of the companies which make such ammo is
Israeli, and they've been fairly aggressive with their marketting. The
Swedish armed forces use the Bofors Defence 40mm and 57mm 3P ammo which
has a side-looking radar built into the fuse, but I don't know if it's
sensitive enough to trig on humans (it's mainly intended as an AA
round, but works pretty well as a roof-hitter against lighter vehicles
too. Against infantry you're supposed to use its pre-set distance
detonation mode anyway <g>) - and besides a 40mm cannon is an RFAC/2,
not a HVC <g> 57mm guns might possibly squeeze by as HVC/3 instead of
RFAC/2, but we only have them on naval craft and not on AFVs.)

>They'd make a pretty effective beehive if I'm not mistaken.

True beehive rounds (flechette "canisters" which burst open at the
muzzle) are even nastier than HE (the beaten area is *much* bigger),
but they're very short-ranged (about 200m for the biggest ones, ie.
DSII "close assault" range). I guess one reason why the USAR doesn't
have any beehives for the Abrams tanks is that the muzzle blast itself
is lethal to unprotected lungs within that distance :-/

>Some of the rounds might actually have explosive contianed within. 

Of course they do. It's hard to get them to fragment at a pre-set
distance
otherwise, like...

>HKP - I think these rounds could work the same as HVC rounds. 

According to the PSB description in DSII, HKPs are low-calibre weapons.
This means they don't have nearly as much space for explosives, nor
material to turn into shrapnel, as HVC rounds of a similar "size class"
do. A HE shell for a HKP/5 is unlikely to be much bigger than a shell
for an RFAC/2, and the HKP doesn't have the RFAC's high rate of fire. 
 
FWIW, I *hate* the PSB description of HKPs. It makes no sense
whatsoever.

>DFFG - DFFGs like the ones on the Phalanx APC are obviously rapid
>fire multi barrell versions of the Infantry Plasma Gun. Not pleasant!
And
>the larger ones probably have larger explosive effects which can hurt
>infantry. In fact, they may even be able to adjust the size/intensity
of the
>burst. 

Adjusting the size/intensity isn't that likely if they're "pre-packed"
with
all the fuel provided in the ammo (which the PSB description in DSII
says it is). If the vehicle provides the fuel "separately", it
shouldn't be too hard to adjust the burst intensity.
 
>HEL - Instead of taking one super high intensity pulse or a long
>tracking beam to kill a tank, turn onto short, medium intensity pulses
>that will cook infantry like a laser machine gun. Not something I'd
want >to see. In fact a Laser SAW, if they ever perfect it, will be
easy to aim, >have little or no recoil, and will leave nasty burns as
it causes water in >the tissues to sublimate blowing big chunks out of
the squishy human.

I thought sublimation was when you go directly from solid state to gas
without melting? If the human is frozen that solid, he's not very
squishy any more <g> But yes, a high-power laser is nasty. The biggest
problem is to get a reliable and man-portable power supply.

>Also note, set on very wide aperature, no doubt mass blindings or
>surface skin burnings could be administered. 

Mass blindings are unlikely if troops have visors or goggles - it's not
too
hard to include anti-laser protection in those, and it'd be outright
stupid
not to if laser weapons are in use (on either side).

>GMS - Expensive, but feasible. Cannister heads, gas warheads, other
>kinds of scatterable chemical or biological agents. 

Chemicals and bio-agents can work (though a GMS warhead is rather
small), but unless you're fighting aliens with a radically different
biochemistry I don't think you really want to use them against a target
a mere couple of clicks away :-/

>Just plain big ass HE. Flechettes fired by a charge. Napalm. 

These all work fine. GMS have limited ammo in SGII though, so you need
to decide what mix of warheads you want before you enter combat.

>MDC/GAC - For the large MDC, perhaps there are splintering
>projectiles or explosive ones.

MDCs have problems similar to those of the HKPs - too low a calibre to
fire effective HE round. The MDC has the ROF to use lots of small
shells effectively though, so can use the RFAC approach.

>Or perhaps they can fire shorter ones at a higher ROF to engage
>infantry. For the small MDCs, they seem ideally suited to
anti-infantry. 

Yep. Super-heavy machinegun, like.

>With these technologies, plus anti-infantry charges, SAWs, etc,
>infantry attacking armour in 2183 might have a hell of a rough time
(esp
>with reactive armour and PDS to reduce the threat of GMS). 

If you have PDS, your reactive armour is more useful if optimized
against long-rod penetrators. Makes it a hell for other vehicles to
take you out too :-/

However, body armour is rapidly getting better (lighter and easier to
wear as well as harder to penetrate, particularly for shrapnel), and
many troops in SGII - particularly the regulars - do carry body armour.
In this light, the D8 impact for a beehive or HE round maybe isn't too
badly off - against an unprotected person (D4 "armour") it's got a very
good chance to wound or kill, but it drops quickly if the victim is
armoured.

>However - and this is the clincher - Jon wanted SG2 to be an
*infantry* 
>game.

It's pretty easy to keep SGII an infantry game. You need to do is to
make sure that the terrain is close enough that the vehicle can't use
its
(much superior) weapons range, though. If you make the battlefield too
open infantry will *and should* suffer - it never has been, and most
likely never will be, able to able to stand up to armoured vehicles in
an open field. No matter how hard I and my collegues try to upgrade the
infantry's anti-armour weapons :-/

Regards,

Oerjan Ohlson
oerjan.ohlson@telia.com

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