Thursday, October 13, 2016

Sword: Bringing the HEAT

This guy looks pretty happy... Not going to lie, I'd be too.
Relatively cheap and able to pack a surprisingly powerful punch in a light weight weapon, nothing puts a pit in heavy armors stomach quiet like a HEAT round.

Have you every wanted to take a look into how they are stated up in GURPS or wanted to come up with your own custom HEAT weapons? Well follow me after the jump for some explosive writing!

Still with me after that gut punch of a bad pun?


Now before we get started, first lets have a quick over review on how a HEAT weapons works.

High Explosive, Anti-Tank, or HEAT are a type of specialized chemical explosive weapons optimized for armor penetration.Taking advantage of the Munroe effect, HEAT weapons are a type of shaped-charge that detonates a given amount of explosives into a cone that has a liner of ductile, high density metal (commonly copper but other metals such as molybdenum and tungsten have been used). The extreme pressure caused by the explosion being funneled into the cones turns the metal liner into a high velocity jet moving at speeds up to 14,000 m/s2! Do to this, the metal lined jet impacts with such force that whatever is hit, its material strength becomes effectively irrelevant and instead acts more like a thick liquid then a solid object.

Do to this, HEAT rounds can achieve extremely deep penetration even into harden steel. The depth of penetration is surprisingly consistent with a HEAT weapons diameter leading to the phrase, "Fist to finger" to describe it's effects with modern weapons having claims of being able to penetrate an amount of RHA equivalent equal to upwards of 14 times the warheads diameter (though in practice this is only under very precise conditions and practical penetration is only around half that in real life situations).

The penetrating jet however can only achieve maximum penetration within a very specific "stand off" distance. If the HEAT weapon detonates to far from the target then the supersonic jet bleeds off velocity do to drag at an alarming rate, if it detonates to close then the jet doesn't have enough time to properly form and basically "splats" against the material spreading its force over a greater area. The need for this precise distance is why some HEAT weapons have a long rode shaped probe jutting out from their front.

It's also the key to exploiting this weapons weakness, but more on that in a later post...

Pretty neat stuff right? Well, I know you guys didn't come here for that. I just need to give an idea of how this stuff works.

Now on to the good old fashion crunch!

Below you will find the rules you need to stat up your very own Ultra-Tech HEAT rounds. These rules are meant to be used for TL9+ weapons and expand on the rules found in Ultra-Tech and updates them to line up with High-Tech.

These rules cover:
  • Standard HEAT weapons(or what Ultra-Tech calls Shaped Charges on pg. 154). The no longer cause fragmentation damage with their linked crushing explosive damage.
  • High Explosive, Duel Purpose, or HEDP weapons, which Ultra-Tech calls High Explosive, Multi-Purpose, or HEMP (see Ultra-Tech pg. 155). In Ultra-Tech theses are just treated at TL10 Shaped Charges and have no real differences in performance compared to normal Shaped Charges, this design system changes this reflect both how HEMP rounds work in both High-Tech and real life. Here they trade some degree of penetrating power for an increased secondary blast blast effect and anti-personal fragmentation. 
  • MS-HEAT, Multistage-HEAT, also know as tandem charges, are not covered specifically but can still be designed using these rules. Just build two HEAT weapons and put them together, one should be declared the probing penetrator and should only be 50-60% the diameter of the main charge. See High-Tech pg. 170 for the rules on how MS-HEAT weapons work.

While technically shaped charge weapons, Explosively Formed Projectile and similar weapons are beyond the scope of these rules and will not be covered here (though perhaps in a later post).

See High-Tech pg. 170 for more on how HEAT weapons work in GURPS.

Part I: Assumptions
First think up some base ideas on what you want for you HEAT weapons, what is the Tech Level it is built at, what is it being designed to be used against and how it is going to be deployed and how advanced it is compared to other examples in the setting. Be sure to draw inspiration from real world designs.

Phenomenal power, itty-bitty living space
Example: Let's make a large but still man portable HEAT round. It's going to be designed to be used on the ultra-tech battlefield where advanced armor is common place and Heavy Battlesuit are a threat. Do to this a simple but powerful Heat round that can be issued out in mass to the troops and used to even greater effect by Heavy Battlesuits is needed. It will be an "over-caliber" design meant to be fired from a simple shoulder mounted launch system like modern RPGs or the German PZF3.

Choose Your Tech Level
This can be TL9, TL10, TL11 or TL12. Higher Tech levels have more penetrating power for their size.

Example: Since I want this to be a weapons used both by and against Heavy Battlesuits it makes sense for it to be TL10. 

Choose your Weapons Diameter
Choose you weapons diameter in sane units millimeters. All things being equal, the greater the HEAT rounds diameter, the better it will penetrate. Of course this also makes the weapons bigger, heavier and costlier.

Minimum warhead size is 18.5mm at TL9, 10mm at TL10+. This is retcon of Ultra-Tech since even today we can develop HEAT rounds that can fit into a shotgun slug! Granted they are not very effective but it is likely that will be worked out by TL9.

Example: Looking over real world examples, it seems that 100-127mm tend to be the high end for a man portable unit, let's settle for somewhere in the middleish at 110mm since it lines up with most modern over-caliber weapons.

Step II: Application
Now that you have your assumptions figured out let's move on to how to use them.

Now let's figure out how much damage your HEAT weapon does.

 Dice of Damage = (Wd×0.26×TL)/Wt

Wd is the warheads diameter in millimeters.
TL is 2.1 at TL9, 2.4 at TL10, 2.7 at TL11 and 3 at TL12.
Wt is 1 if the warhead is standard HEAT, 1.5 if HEDP.

 A HEAT weapons does crushing damage with the explosive modifier and a Armor Divisor of (10).

Example: Our 110mm HEAT round is TL10 and a standard HEAT round and there for does 110×0.26×2.4×1 or 68.6 dice of damage which which we can condense to 6d×11(10) cr ex.

Linked Explosive Blast
Along with the main penetrating blast, HEAT weapons also produce a smaller linked area effect explosion.

 Dice of Damage = Wd(3/2)×Wt

Wd is the warheads diameter in millimeters.
Wt is 0.016 if the warhead is standard HEAT, 0.029 if HEDP.

The linked area effect explosion does crushing damage with the explosive modifier.

Example: Since our warhead is 110mm and a standard HEAT, it's linked explosive damage is 110(3/2)×0.016 or 18.45 dice, which we can condense to 6d×3 cr ex. This will be noted as being linked to the main penetrating blast.

Fragmentation Damage
HEDP rounds also produce fragments with their linked explosive damage, HEAT rounds only produce incidental fragments. Note this damage in brackets ("[]") and

Fragment Dice of Damage =Wd/20

Wd is the warheads diameter in millimeters.

Example: If this was an HEDP warhead it would also produce fragments which would of been equal to 110/20 or 5.5 dice worth of fragments which would be recorded as [5d+2].

HEAT Warhead Weight

Warhead Weight = Wd3×0.0000019lbs

Wd is the warheads diameter in millimeters.

Example: Being a 110mm warhead, it weighs 1103×0.0000019 or 2.5lbs. 

HEAT Warhead Cost

Warhead Cost = Wt×$40

Example: Since our warhead weights 2.5lbs it costs 2.5×$40 or $100.

Legal Class
Given that unlike normal shaped charges, HEAT rounds have no non-military use, they are counted as LC1.

Wrapping It UP
Once you got everything work out just stat up nice and neat like this:

TL Warhead            Damage                    Cost     LC
10  110mm HEAT    6d×11(10) cr ex       $100        1
      linked                6d×3 cr ex


  1. The weight for the warheads seems very light when compared to what conventional ammunition weighs in Ultra-Tech.
    a 100mm cannon round weighs 40lbs in the Conventional Ammunition Table (UT139), but using your article comes out at 1.9lbs using your formula.
    The weight is also $76, while UT139 says $400.

    Am I missing something?

    1. That's just the weight of the warhead. While Ultra-Tech doesn't out right list the weights of the warheads it does give us the means of figuring it out. You know that the striker and hunter missile from pg. 169 of Ultra-Tech? The hunter missile has a 64mm warhead, ST3 and 3 levels of payload which works out to a warhead weight of about half a pound. The striker missile has a 100mm warhead, ST6 and also has 3 levels of payload which works out to about 2lbs of warhead weight which is right for a warhead with a volume 8 times larger then the 64mm one.

      I just extrapolated from there to get my weight formula.

      Now for the cost, a 64mm warhead costs $10 as a base which is doubled to $20 for being a HEAT round, this means they cost $40 a pound.

  2. This feels like it's just the weight of the warhead itself. Perhaps a bit more weight should be added to account for the rest of the shell or rocket?

    1. That's what it is and yeah I do feel they are a bit light but since this is meant to be compatible with Ultra-Tech I had to use the weight value David choose for his warheads.

      See my reply to Johnathan Maw for how I came up with my numbers.

  3. I might get this a go sometime soon, as I do have a need for HEAT rounds in mind, though at TL8. Where's the formula from? I don't think it was in UT or HT (rules for applying it to a warhead, sure). Could it be applied to TL7 or TL8 as well (would need TL modifier) or is it best to just stick with what HT gives us?

    1. Oh I backwards engineered the stats based on my knowledge of how HEAT rounds work. For modern HEAT rounds look up how many inches of RHA equivalent it can punch through, times it by 7 and divide that total by 3.5 to get how dice of damage it has. If you can't find this information then as a rule of thumb a TL8 HEAT round will punch through 6.5 times it diameter in RHA equivalent, a TL7 on will do 5 times and while I haven't studied up on TL6 HEAT I'm ngoni get to guess it penetrates 3 times its diameter.

      All the other stats should work as is.

    2. Ah, roger. I'll put some of this to use eventually, I'm sure; just a matter of getting through the dozens of TO DO articles!