GURPS Special Ops blog

[MrFix]

Originally Posted by fula farbrorn

its hull is also blast optimised. reducing effects felt on the passengers by putting them in a capsule together with crew.

Perhaps the bottom of the crew capsule should have 110 DR (or however much), rather than generally the bottom of the vehicle. That way the vehicle explodes, wheels fall off etc and it is no longer mobile, but the crew gets that DR vs damage to occupants on attacks from the bottom.

[sjolly75]

Originally Posted by fula farbrorn

The Oshkosh is usually STANAG 4569 Level 2 which would equate to 25-30 DR

but it can be uparmored to Level 3, protection from 7.62 Nato M993, which should be 50 DR.

its hull is also blast optimised. reducing effects felt on the passengers by putting them in a capsule together with crew.

Ok... I think I might be missing some relevant conversion info. Any useful tips on converting real life armor into DR?

[sjolly75]

Originally Posted by MrFix

Perhaps the bottom of the crew capsule should have 110 DR (or however much), rather than generally the bottom of the vehicle. That way the vehicle explodes, wheels fall off etc and it is no longer mobile, but the crew gets that DR vs damage to occupants on attacks from the bottom.

Good call. That's really what I was trying to emulate - the crew being protected but the vehicle is pretty much mangled.

[MrFix]

Originally Posted by sjolly75

Ok... I think I might be missing some relevant conversion info. Any useful tips on converting real life armor into DR?

70 DR = 1" RHA

If armor protects against specific projectile, find it's GURPS stats, then find it's average damage.

7.62 M993 is 7.62x51 APHC that deals 7d (2) pi- damage.
XSAPI armor stops 7.62 M993
Thus XSAPI armor would have
7*3.5(average of d6)=24.5
24.5*2(the armor divisor)=49 DR.

GURPS stats DR based on assumption that armor stops the projectile it's rated for 50% of the time. Hence average of d6 in that formula.

[FrackingBiscuit]

Just spitballing about underside blast protection, both for the M-ATV and for other vehicles you might want to cover. Aside from just armoring the bottom, on modern vehicles this usually comes in the form of redirecting the force of an explosion away from the occupants, using either a V-shaped hull or (as in the M-ATV), a crew capsule that physically separates the crew and their seats from the floor of the vehicle. The result is greatly increased crew survivability without the huge weight gain of very thick armor.

Rather than just have a higher DR on the underside, which would protect from any attack, it might be better to specify that it has a split underside DR (or split crew capsule DR, following MrFix's suggestion). One value representing the actual armor (or lack thereof, as the case might be), and a second higher value for any crushing explosion damage that isn't a shaped charge.

Alternatively, maybe a damage divisor (the opposite of an armor divisor) might be better. Since energy is being redirected around/through vehicle, it might be more accurate to think of the energy (and thus the damage) as being divided, so that even very large explosions can be survivable.

There would probably be two different versions of this - V-shaped hull, and anti-blast crew compartment. The crew compartment would leave the vehicle's DR unchanged, but provide a damage divisor for the crew against any crushing explosion that isn't a shaped charge. The vehicle might be wrecked, but the crew could be relatively unharmed. A V-shaped hull would provide the vehicle itself as well as the occupants with the damage divisor. A drawback of a V-shaped hull is that since the energy is directed around the sides of the vehicle, there's a good chance of the wheels being blown off - a crushing explosion attack against the underside of the body would apply some of the damage to the wheels/treads. The double-V hull would come with a larger divisor, while having both a V-hull and anti-blast crew compartment would give the vehicle a damage divisor and the crew a higher divisor.

In short:

1. Anti-Blast Crew Compartment - gives crew a damage divisor of 2 against crushing explosion damage originating from under the vehicle. Vehicle is unaffected. Doe not affect shaped charges.
2. V-Shaped Hull - gives crew and vehicle a damage divisor of 2 against crushing explosion damage originating from under the vehicle. Any such attack that hit the body of the vehicle also hits the wheels/treads of the vehicle, as they absorb some of the redirected energy. Use the same base damage, and apply a 3 armor divisor (representing the smaller amount of damage divided between each location). Possibly require a d6 roll beforehand to see if damage applies.
3. Double-V Hull - as above, but increase the crew and vehicle damage divisor to 3.
4. V-Shaped Hull + Anti-Blast Crew Compartment - as a V-Shaped Hull or Double-V hull, but increase the Crew Compartment damage divisor by 1 (resulting in 3 for a V-Hull and 4 for a Double-V Hull).

Or a simpler system of basic and advanced protection, giving a 2 damage divisor (V-hull, crew capsule) or 3 (double V-hull, or V-hull + crew capsule). With a note for which vehicles use V-hulls and therefore might suffer wheel damage, or just ignore it.

As for the actual damage divisor examples, it would be best to look up how big of a bomb the vehicles are rated to survive (shouldn't be too hard to find, since manufacturers will want to advertise their advanced protection), calculate how much damage that many kg/lbs of explosive would do, and pick a divisor that would let the underside DR protect against that damage (following the method MrFix posted).

But then, maybe this is all too complicated for a roleplaying game. Is this helpful at all? Am I over-thinking/over-complicating it? How often will players run over mines/IEDs anyway?

[MrFix]

Originally Posted by FrackingBiscuit

Anti-Blast Crew Compartment - gives crew a damage divisor of 2 against crushing explosion damage originating from under the vehicle. Vehicle is unaffected. Doe not affect shaped charges.
V-Shaped Hull - gives crew and vehicle a damage divisor of 2 against crushing explosion damage originating from under the vehicle. Any such attack that hit the body of the vehicle also hits the wheels/treads of the vehicle, as they absorb some of the redirected energy. Use the same base damage, and apply a 3 armor divisor (representing the smaller amount of damage divided between each location). Possibly require a d6 roll beforehand to see if damage applies.
Double-V Hull - as above, but increase the crew and vehicle damage divisor to 3.
V-Shaped Hull + Anti-Blast Crew Compartment - as a V-Shaped Hull or Double-V hull, but increase the Crew Compartment damage divisor by 1 (resulting in 3 for a V-Hull and 4 for a Double-V Hull).

By default, in a closed vehicle, crew never takes cr ex damage, B555. They take 1d cutting (and only cutting) damage per 5 points of penetrating damage to the vehicle. This is meant to simulate the vehicle's pieces flying inward at the crew under damage.