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Old 06-05-2019, 03:40 PM   #1
FeiLin
 
Join Date: Aug 2018
Default 4th WWII Vehicle conversion

I'm drooling over the awesome tanks and vehicles in 3rd WWII A World Ablaze, and want to use them in 4th.

Primary goal is to take any (at least WWII at this point) vehicle/aircraft/ship from 3rd and convert the stats to 4th, which means I'm gunning for ST/HP, Hnd/SR, HT, Acceleration, Top Speed, SM, Armor (per facing) and weapons. I tried to compare the stuff I could find in HT, namely Panzer IV, Sherman, Mustang, Jeep, and 2 1/2 ton truck, as well as improvise the low TL heavy motorcycle from basic and the APC (which kinda had equivalents in WWII).
  1. ST/HP: I was on the verge of just dividing land vehicles by 10 and air by 3/2, but then I found another thread which suggested cube root of HPs *12. I found cube root *13 gave almost spot on for the examples.
  2. Hnd: gMR*4 -4 gave a close enough result. For aSR it was aSRų2 -3. I couldn't find any comparable watercraft, unfortunately.
  3. SR: SR seems close enough for a/g/wSR.
  4. HT: This seems about the same, although there were some deviations between WWII and HT (Mustang went from 8 to 11, for example, which is a cheap to fairly good quality change). I was also a bit surprised about the Tiger at 8, but I guess it's more about it's sub-par construction quirks than the actual robustness in combat (instead represented by DR etc).
  5. Acceleration: This is a bit messy and hard, because it's such small numbers (compare 2 in acceleration with 3 for a 50% boost...), but I found just take the gAccel (or wAccel?) as is, and divide air by 2 (I dont know why, but that gave me ok results).
  6. Top Speed: Divide by two.
  7. SM: I was hoping that it would be convertible by taking the body to hit modifier, but I think it's better to calculate SM by taking dimensions in the SSR table.
  8. Armor: Take 80% and round up (important for at smaller values, such as fighters).
  9. Weapons: I'm a bit unsure in general about the weapons. They seemed somewhat similar, but I have no idea what the rules behind 3rd are, but for instance damage types and damage modifiers seemed to be new to 4th. Anyone have any advice for this?

Disclaimer: I don't know much about 3rd in general, and I have no idea how PD works. Nor did I plow all the details with sloping armor, to hit bonuses from tank chassis, or really much of the rule related stuff in 3rd.

Also, the HPs for 3rd were about 10 times higher whereas the DR were maybe 30% higher, and weapons seemed to my untrained eye of roughly the same size, so does PD have that great impact or are there other explanations for this difference?
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Old 06-05-2019, 05:02 PM   #2
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Default Re: 4th WWII Vehicle conversion

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Originally Posted by FeiLin View Post
Disclaimer: I don't know much about 3rd in general, and I have no idea how PD works. Nor did I plow all the details with sloping armor, to hit bonuses from tank chassis, or really much of the rule related stuff in 3rd.
4e doesn't use PD so you can ignore it. Sloping also increases effective armor thickness at the cost of wasted space in the vehicle.

The to-hit bonuses for tank chassis are just bonuses for target size.
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Old 06-05-2019, 05:52 PM   #3
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Default Re: 4th WWII Vehicle conversion

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Originally Posted by FeiLin View Post
Also, the HPs for 3rd were about 10 times higher whereas the DR were maybe 30% higher, and weapons seemed to my untrained eye of roughly the same size, so does PD have that great impact or are there other explanations for this difference?
Hit Points in 4e are derived in quite a different way. The RAW method for getting HP in 4e is to take the cube root of weight times 4 for vehicles.

As for DR differences, it's probably a matter of how the authors treated sloping and what a few other assumptions.

Bullets in 3e behave much like they do in 3e, but in 4e the damage multipliers for bullet size were codified. Thus even though in 3e they are given as doing crush damage, it's effectively the same as in 4e, so just take the damage as being pi or pi+ or whatever would be appropriate in 4e, with the same number of dice and penetration modifiers as it's given in the 3e source.

This, BTW, gives a check on the DR levels - check the 3e WWII stats for the Pz.IV and M4 tank guns against the 4e versions.
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Old 06-05-2019, 06:44 PM   #4
Fred Brackin
 
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Default Re: 4th WWII Vehicle conversion

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Originally Posted by FeiLin View Post
I
Also, the HPs for 3rd were about 10 times higher whereas the DR were maybe 30% higher, and weapons seemed to my untrained eye of roughly the same size, so does PD have that great impact or are there other explanations for this difference?
The authors of the WWII line had idiosnycratic ideas anout vehicle armor and direct conversions from the WWII line to other parts of Gurps (either 3e or 4e) do not work well.

Anywhere else in Gurps (3e or 4e) 25mm of Rolled Homogenous Alloy or RHA equals DR 70 and no conversion is neccesary.

Don't worry about PD. It has vanished from Gurps and no note of its' passing need be taken. It's just gone.
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Old 06-05-2019, 08:19 PM   #5
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Default Re: 4th WWII Vehicle conversion

WWII used DR84/inch, did it not? That would mean converting to 4e would require multiplying by x0.83 to thereabouts.
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Old 06-05-2019, 11:01 PM   #6
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Default Re: 4th WWII Vehicle conversion

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WWII used DR84/inch, did it not? That would mean converting to 4e would require multiplying by x0.83 to thereabouts.
DR 70/inch for cheap armor, DR 82/inch for standard, DR 98/inch for expensive and DR 122/inch for advanced (p.142, box).
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Old 06-06-2019, 09:37 AM   #7
Fred Brackin
 
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Default Re: 4th WWII Vehicle conversion

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Originally Posted by copeab View Post
DR 70/inch for cheap armor, DR 82/inch for standard, DR 98/inch for expensive and DR 122/inch for advanced (p.142, box).
In other iterations of Gurps the Expensive is the DR 70 RHA, the Standard is probably Mild Steel at c. DR 50 and the Cheap is some sort of iron that could be produced at TL4.
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Old 06-08-2019, 04:55 AM   #8
FeiLin
 
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Default Re: 4th WWII Vehicle conversion

Great, thanks for all the input!!

For to hit, I'll use the rules for calculating SM from the SSR table, and base the location penalties on that (large or small turrets, caterpillar tracks, wings etc already exist).

Though I have a few other follow-ups:
  1. Weapon check: I did a check of main guns for Panzer IV and Sherman against the front and rear body DR for 3rd and 4th respectively, and that made me a bit perplexed. 4th HP is about a tenth, and DR is around 83%, while the damage seems to me higher. The ďregularĒ dice for APEX are higher, thereís the pi++ which modifies damage after DR (Iím unsure if 3rd has that), and the follow-up is also higher and has the ex trait (again unsure about 3rd). All in all, with all these factors making it easier for a gun to reduce a tank to 0 HP, unless 3rd has a lot of rules in its Basic/HT, it seems tanks die much quicker in 4th. I mustíve missed something; do tanks bleed in 3rd?
  2. AA Weaponry: I was trying to find some of the AA weapons, such as the 88mm AA gun (KwK36/FlaK18/FlaK36); which 4th stats come closest to that? Also, I couldnít find a 20mm AA autocannon (FlaK30/KwK30/FlaK38/KwK38); which are the most similar? With the question above Iím not sure if itís relevant to just take them as is or if I should adjust them first. If I should just take them as is, how would I decide what's "appropriate" regarding pi/pi+/pi++ and other stats (aside from looking at similar calibers/makes and arbitrarily deciding)?
  3. RHA DR: Where in 4th does it say 70 DR/25 mm of RHA? Donít doubt it, but couldnít find it.
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Old 06-08-2019, 10:58 AM   #9
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Default Re: 4th WWII Vehicle conversion

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Originally Posted by Fred Brackin View Post
In other iterations of Gurps the Expensive is the DR 70 RHA, the Standard is probably Mild Steel at c. DR 50 and the Cheap is some sort of iron that could be produced at TL4.
My recollection, which seems to be a bit dodgy just now, is that mild steel came out at DR56 (80% of RHA's DR).
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Old 06-08-2019, 09:58 AM   #10
Anaraxes
 
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Default Re: 4th WWII Vehicle conversion

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Originally Posted by FeiLin View Post
I have no idea how PD works
Just to help you interpret 3e stats, armor before 4e had both DR and a "Passive Defense" rating. PD supposedly reflects the possibility that your armor could just turn/deflect/bounce a blow, as opposed to just not get penetrated by a solid, direct hit (which is DR). It was added to Active Defense/2. Note that this gives you a chance to defend even if you don't have an AD. PDs in 3e for low-tech humanoid armor were in the 2-4 range, with a max of (IIRC) 7 for plate armor.

The "3" in the 4e formula for defense (3 + skill / 2 + DB) is a vestige of PD, effectively declaring that all armor always has PD 3. Defenses would be pretty low without that +3, and of course the mechanics had been designed assuming there was some PD involved. You can also see echoes in the Magic armor enchantment spells. "Fortify" and "Deflect" were +DR and +PD; without PD, Deflect turned into +DB (mechanically similar, but the name shows the old PD flavor rather than the "massive shield block" image of DB).
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