Designing Ultra-Tech armor loadouts with Pyramid #3/85 and #3/96

[Varyon]

Originally Posted by Rupert

No, GURPS doesn't. A DR35 vest is one that's rated to stop 7.62x51mm AP rounds.

To be fair, of the two DR 35 vests in HT, one (Advanced Body Armor) is based on the debunked Dragonskin, and the other (Assault Vest) is based on the Interceptor OTV, which can have SAPI (with the vest, rated against 7.62x51mm Ball Ammo, typically 7d pi) or ESAPI (with the vest, rated against .30-06 AP, typically 5d(2) pi-) plates, but HT doesn't state which is in the table. Because we're fairly consistently told that GURPS authors try to rate firearms and armor based on average penetration, it's more likely the author of that section of HT opted for the stronger ESAPI plates. This is further suggested by the mention in the Assault Vest's text that it is "the current U.S. military-issue vest in Iraq and Afghanistan." As HT's publication date (2007) is after the US largely switched from SAPI to ESAPI (which occurred in 2005), ESAPI is the most likely. Thus, average damage and DR are set to equal nominal penetration. A high roll on the damage dice is likely to represent a hit that missed (or nicked) the plate, but didn't hit anywhere particularly vital (hence the low damage). It's an abstraction, and one that probably puts the probability of such a hit much higher than it should be in the interest of keeping things, well, interesting.

If this is problematic, the "Armor as Dice" rule (originated on the forums, made RAW in Pyramid #3/34) gets rid of the variability of penetration. The alternative is to decide what value on each dice is more acceptable to you than 3.5 (from your mention of DR 35 protecting against 7d, sounds like you may want to go with 5), and adjust all armor upward. For our example of 5, this means multiplying the DR of all armor (at least in regards to firearm protection) by 5/3.5, or 10/7 (it's roughly x1.4).

Originally Posted by Michael Thayne

Thinking about the issue of how thick limb armor can realistically be while maintaining mobility: a suit of optimized fabric that's nominally 1/4 inch thick could be assumed to be only 1/8 inch thick around the joins, to maintain flexibility? Does that seem reasonable in terms of designing a suit ordinary soldiers could realistically wear while out on patrol without losing too much in terms of mobility?

My general rule of thumb is that flexible armor can be up to 1 inch thick on the Skull, Face, and Chest, up to 0.25" thick where LT puts armor gaps*, and 0.5" thick everywhere else. Rigid armor can be up to 0.4" thick on the Chest (front and back) or Skull, cannot be present at armor gaps (hence why they are gaps), and up to 0.2" thick elsewhere. Changing rigid armor to be 0.5"-NO-0.25" probably wouldn't break anything, and arguably be a bit more cohesive. Semi-rigid armor, like scale, I might allow for something like 0.05" to protect the armor gaps. Thicker than this is possible (indeed, I think some historical and modern armor exceeds these guidelines), but should result in some sort of DX penalty. How much, I'm not sure... maybe -1 per +20%? That would be -5 to DX if your armor is twice as thick as allowed.

For where I came up with these values, 0.5" is fairly consistent with the Max DR values for most flexible materials in the articles, while 0.2" is fairly consistent with the Max DR values for most of the rigid materials. 0.25" is noted in the articles as the maximum thickness at which armor remains flexible (technically, it says "no more than 25% of its listed DR/in"), so seemed appropriate for gaps, which would require truly flexible armor. It seemed to me the Chest and Head (Skull and Face) don't need to support the range of motion of other locations, so they could be thicker; I opted for x2 as the joints were x1/2, but one could easily justify +50% instead (as the joints are -50%).

*I'm tempted to extend the gaps a bit, with rigid cuisses (thigh protection) giving at best 5/6 protection to the thighs; this would eliminate the DX penalty suggested in Loadouts. Expertly and Masterfully Tailored armor would be allowed to have full protection, with the LT armor gap targeted at a total of -7 for Expert, -8 for Masterful. Similarly, rigid gorgets (neck protection) would probably have a similar limit to them (indeed, I'm tempted to limit that to 4/6, with Expertly Tailored getting 5/6 and Masterfully Tailored being full protection with the normal -8 to target the gaps).

[Michael Thayne]

Originally Posted by Varyon

To be fair, of the two DR 35 vests in HT, one (Advanced Body Armor) is based on the debunked Dragonskin, and the other (Assault Vest) is based on the Interceptor OTV, which can have SAPI (with the vest, rated against 7.62x51mm Ball Ammo, typically 7d pi) or ESAPI (with the vest, rated against .30-06 AP, typically 5d(2) pi-) plates, but HT doesn't state which is in the table. Because we're fairly consistently told that GURPS authors try to rate firearms and armor based on average penetration, it's more likely the author of that section of HT opted for the stronger ESAPI plates. This is further suggested by the mention in the Assault Vest's text that it is "the current U.S. military-issue vest in Iraq and Afghanistan." As HT's publication date (2007) is after the US largely switched from SAPI to ESAPI (which occurred in 2005), ESAPI is the most likely. Thus, average damage and DR are set to equal nominal penetration. A high roll on the damage dice is likely to represent a hit that missed (or nicked) the plate, but didn't hit anywhere particularly vital (hence the low damage). It's an abstraction, and one that probably puts the probability of such a hit much higher than it should be in the interest of keeping things, well, interesting.

This is an interesting theory but the Tactical Vest in Characters has identical stats aside from being 2 lbs. heavier, and Characters came out in 2004, which was before the military started introducing ESAPI.

[Anthony]

Far as I know it has DR 35 because it's supposed to stop 5.56mmAP, and a level IV vest is supposed to stop 7.52mmAP and thus DR 50. This means a level III vest also stops 7.62 ball, so it might have been better to add a level of Hardened, but you do need the DR 35.

[Michael Thayne]

Originally Posted by Anthony

Far as I know it has DR 35 because it's supposed to stop 5.56mmAP, and a level IV vest is supposed to stop 7.52mmAP and thus DR 50. This means a level III vest also stops 7.62 ball, so it might have been better to add a level of Hardened, but you do need the DR 35.

Were widely-used tactical vests circa 2004 designed to stop 5.56mmAP? Can't find any indication this was the case.

[Rupert]

7.62x51mm NATO ball does 7d pi, so by GURPS' reckoning (also used in the two articles the OP refers to) that's around DR23. Boring old AP does 5d(2) pi-, and thus needs around DR35, as does 5.56x45mm APHC. 7.62x39mm API doing 4d-1(2) pi- inc is fairly common and it takes DR26 to protect against it.

Hence DR25 and DR35 for vests plus plates in the Basic Set, and similar numbers in HT.

DR12 is level IIIA (.44 magnum level protection), which is why the better vests give that as their level of flexible protection.

[Anthony]

Originally Posted by Michael Thayne

Were widely-used tactical vests circa 2004 designed to stop 5.56mmAP? Can't find any indication this was the case.

I misremembered, level III is actually rated to stop M80 ball (so it needs DR 25), level IV to stop M2 AP (so it needs DR 50). In reality, the penetration difference between those M2 and M80 is not a factor of two, nor is the weight different by a factor of 2, so you should expect level III to have 60-70% of the DR of level IV (DR 30-35). I'm not actually sure what 5.56mm ammo would be called 'AP', M995 should be the same type as M993 (just a different caliber), and M993 can penetrate level IV.

[Varyon]

Originally Posted by Michael Thayne

This is an interesting theory but the Tactical Vest in Characters has identical stats aside from being 2 lbs. heavier, and Characters came out in 2004, which was before the military started introducing ESAPI.

Does that armor state what, if any, real-world armor it is based upon? It’s entirely possible the authors decided level IV armor was needed, and extrapolated from current designs and research what it would likely weigh (and note ESAPI was in active use only a year after 4e was released). Even if we assume the armor in Characters was designed assuming a roll of 5 on each dice (rather than 3.5), this clearly changed by the time High Tech was released, as the two armors there that are DR 35 - OTV with ESAPI and Dragonskin - were both (thought to be) NIJ level IV at the time of writing/publication. NIJ level IV is proof (for one shot) against a round GURPS states is 5d(2), which matches up exactly with what unhardened DR 35 will protect against on an average-damage (that is, 3.5 per dice) roll.

Now, nothing is stopping you from using the armor design articles to make your armor to a higher standard, shooting for DR 35 for level III and DR 50 for level IV, but don’t be surprised when your armor ends up heavier than the real-world equivalents.

[Michael Thayne]

Originally Posted by Varyon

Even if we assume the armor in Characters was designed assuming a roll of 5 on each dice (rather than 3.5), this clearly changed by the time High Tech was released, as the two armors there that are DR 35 - OTV with ESAPI and Dragonskin - were both (thought to be) NIJ level IV at the time of writing/publication. NIJ level IV is proof (for one shot) against a round GURPS states is 5d(2), which matches up exactly with what unhardened DR 35 will protect against on an average-damage (that is, 3.5 per dice) roll.

I don't think High-Tech specified which version of the OTV was being described, and Wikipedia has Dragon Skin at allegedly only level III. And when Pyramid #3/57 did "Improved Assault Armor", it was explicit about giving SAPI DR +25 (37 total with the vest), while "Enhanced Ballistic Plates" (which sounds a lot like ESAPI) gave +30 (42 total). Plates for 7.62mm armor piercing rounds are given DR +35 (47 total). That's not actually straightforwardly consistent with any particular theory of how this stuff is supposed to work—the "Enhanced Ballistic Plates" are giving you a hair over 4 DR (after armor divisors) per die of damage, while the thickest plates give you a bit less than 3.5. So IDK what to say.

[Michael Thayne]

Oh, and here's a refined write-up for the Complete Protective System, that takes into account construction cost modifiers and the fact that a full torso solid plate would stop you from bending at the waist:

20 DR Magnetic Liquid Armor, Fabric, All locations except face (13.216 lbs., $2,643.20)
25 DR Titanium Nanocomposite, Solid, Chest (15.75 lbs., $3,937.50)
10 DR Laminated Polycarbonate, Plate, Face (1.4 lbs., $84)
Sealed, All (neg., $106.75)
Rounded Totals: (30 lbs., $6,800)

[Rupert]

Originally Posted by Anthony

I misremembered, level III is actually rated to stop M80 ball (so it needs DR 25), level IV to stop M2 AP (so it needs DR 50). In reality, the penetration difference between those M2 and M80 is not a factor of two, nor is the weight different by a factor of 2, so you should expect level III to have 60-70% of the DR of level IV (DR 30-35). I'm not actually sure what 5.56mm ammo would be called 'AP', M995 should be the same type as M993 (just a different caliber), and M993 can penetrate level IV.

If you assume that M2 AP ammo is normal AP, not APHC, it only needs DR35 to stop it, which is more consistent with its real life performance.