Mortar fire

[Michele]

Originally Posted by jason taylor

Could infantry mortars pentrate tank rooftops?

"Tank" is a pretty broad concept over six years of desperately fast-paced development. The British Light Tank Mk III had a minimum armor thickness (which I think refers exactly to the top) of 4mm. I think that's pretty thin.

The average (81mm) mortar barrage against the average (mid-to-late) medium tank unit would probably not result in the direct destruction of any of the tanks. However, they could suffer damage to small but important parts like aerials and sights, and less important parts too; near misses and direct hits could still reduce or negate the tank mobility through damage to the tracks/drivetrain/vulnerable engine parts; and they could kill/wound crewmen who were sticking their head out at the wrong time, if they landed on target at the first salvo (unlikely save, as mentioned, in case of pre-plotted fire on observed locations). After that, the barrage would force the crews to button up, which reduces situational awareness. Then there is the effect on morale.

Did they have scatterable mines in WW2?

Definitely, if you mean by air bombing! GURPS WWII: Iron Cross p. 67. It's the SD2 submunition. That's an antipersonnel mine, but the same cluster container could carry, instead, the SD4/HL warheads. "HL" obviously is for Hohlladung, and you don't want to be hit by one of those, even if you are in the heaviest tank. On the down side, the SD4/HLs didn't turn into anti-vehicular mines.

[geppo_68]

Originally Posted by Michele

By the way, could you tell us which kind of mortar you plan to use? I mean, ideally we all like a general, comprehensive rule. But if it will be a 32-cm siege monster, whose crew can see the enemy because of an unexpected turn of events,... then we can, at least for the time being, stop worrying about the gun-mortars, the weird mortar/HMG combo, the small-caliber Japanese 89 Shiki "grenade discharger" and Italian Mod. 35 "assault mortar", and other similarly marginal cases.

It is a classic b movie sci-fi scenario, so earth troops vs aliens and big ants.
A small detachment of insurgents and some regular troops..could be one or two 60 mm mortar up front + one 81mm mortar way back. All very basic and very classic

[Rupert]

Originally Posted by jason taylor

Could infantry mortars pentrate tank rooftops?

Well, a 120mm mortar shell has about the same bang as a 152mm gun-howitzer shell. Those were used to destroy German tanks by the Soviets in WWII. They didn't need to penetrate - the blast could rip the turrets off, and even if it didn't, concuss and injure the crew. I expect a 120mm mortar shell landing on the deck, even if it didn't penetrate, would make a mess of the tank's innards (especially if it landed on the engine air intakes).

[Michele]

Originally Posted by geppo_68

It is a classic b movie sci-fi scenario, so earth troops vs aliens and big ants.
A small detachment of insurgents and some regular troops..could be one or two 60 mm mortar up front + one 81mm mortar way back. All very basic and very classic

Then, if I were you I'd cut a long story short. Give the regulars the 81mm, with a crewman having Artillery (Cannon) and another grunt having Forward Observer, and let them use the mortar in the artillery way.
Remove the 60mms and hand out to the insurgents three or four grenade launchers. They're short-changed as to range, but they are far more likely to have Guns, anyway, than Gunner or Artillery, so they can use those more easily. Also, players will like having their own "hand mortar" more, anyway.

[Anthony]

Also, grenade launchers are more relevant on the time scale of GURPS tactical combat, since you don't have to wait 20-30 seconds for the round to arrive.

[Celjabba]

By the rule, if you are using an heavy weapon, you use

-Gunner for direct-fire attack – (aim and) fire at a close target to which you have LOS**
-Artillery for everything else, indirect fire, firing onto a target area*, or firing at a distant target.

Wether or not the projectile travel on an high ballistic arc is imho irrelevant.

The problem is with artillery weapons that can be used for close target with LOS. Like some mortar, as noted above, but one could argue by a strict rreading of the rules that if you have, for exemple, a deck-mounted torpedo launcher and fire the torpedo at a ship 500m away, you should use gunner(torpedoes)...

*: if the target area is close and within LOS, do you use gunner or artillery ? The rules of suppresion fire and the like seem to indicate gunner.

**: there is an interesting exception, you use artillery(guide missile) to aim and fire a guide missiles recquiring lock at a specific target that you (must/should) have line of sight to. (campaign p413).

Lots of edge case requiring on the spot GM decision between Artillery and Gunner...

[geppo_68]

It seems to me that thanks to some precious posts in this thread, somehow the fog has been cleared.
In sum:
if a projectile-missile fire gun requires high complexity calculation/ ballistics and powder charges tables/ personnel dedicated to observation of results of the shots as feedback and/or map reading target coordinates to be translated in the "gun" adjustments---> Artillery skill
other cases ---> Gunnery skill.
This is true even if the target is in LOS or not.

So if a mortar is a "true mortar" (and not a grenade launcher), with complex adjustments and sights, thought mainly for indirect fire, it will use the Artillery skill in all cases.

Then we will use the Range/ Speed/ size charts in all cases and if we use the Artillery skill we have to use a coupled Forward Observer skill even if the target is in LOS and even by the same person, if necessary.

If we use Artillery, I think we are obliged to declare "area fire", so getting a +4 and losing the possibility to track the target.
In other words, via FO skill we try to predict were the target will be x seconds later, we define the area to hit and then via Artillery we declare an "area fire" on that area.

Makes sense?