Vehicles: 3E vs. 4E

[Fred Brackin]

Originally Posted by lugaid

T). So, the guns do damage that looks very similar between editions.

Okay, I just remember that it was the Sherman gun that one of the devs complained of. Thatt may have been fixed too before publication. It was a very rushed playtest and I was busy trying to break the system doing a P-38. Airplanes were always more my thing.

[Fred Brackin]

Originally Posted by Rupert

It was a perfectly fine gun for its time and intended role

<shrug> Things that are notorious are not always true.

[lugaid]

I'm looking at the numbers for armor in WWII, and they seem to follow the numbers in GURPS Vehicles. So, I'm not sure why there should be any difference at all between the numbers in WWII and fourth edition's High-Tech. Which brings me back to the issue of the numbers seeming to be figured by multiplying the PzIV armor values listed in WWII by 0.9 and rounding down to the nearest 5 or 10 points*, and multiplying the M4A1 armor values by 0.7 (and not needing to round them because they are exactly that)**.

Again, this is a tool I would like to use to make my life easier, given the unusual nature of dieselpunk vehicles, and I am trying to understand why 4E has made the decisions it has relative to the ones that existed in 3E, and this 0.9/0.7 dichotomy is vexing.


*WWII PzIV is listed as DR315 F and DR120 R/L (DR80 B, but this seems to be ignored in the new simplified vehicle paradigm), while High-Tech gives DR280/105. I'm ignoring PD for obvious reasons. 315 × 0.9 is 283.5. 120 × 0.9 is 108.

**WWII has DR300 F and 150 R/L and B, with High-Tech listing it as DR210/105. 300 × 0.7 is 210. 150 × 0.7 is 105.

[Fred Brackin]

Originally Posted by lugaid

I'm looking at the numbers for armor in WWII, and they seem to follow the numbers in GURPS Vehicles. .

You may be looking only at TL6. If you look at the tL6 column in Ve2 you'll see 4 types of metal armor labelled generically "Cheap, Standard, Expensive and Advanced".

It is not until you look at lower TLs that you see that what was "Cheap" at TL 6 was "Expensive" at TL4 and "Standard" at TL5.

So the Cheap metal TL6 armor is something available at TL 4. My guesses are that TL6 armor materials are iron plate for Cheap, mild steel for Standard, RHA for Expensive and a generic Really Good Steel Armor for Advanced.

From memory the WWII devs set TL6 Cheap Metal to be RHA and the three higher grades as progressivly better grades of improved steel armor and figured DR from that. You'll see that they set Cheap armor to be DR 70 per inch.

So WWII not only differs on what is RHA but it differs in the scale of how fine the level of distinctions are that it's trying to use.

[Rupert]

Originally Posted by lugaid

Again, this is a tool I would like to use to make my life easier, given the unusual nature of dieselpunk vehicles, and I am trying to understand why 4E has made the decisions it has relative to the ones that existed in 3E, and this 0.9/0.7 dichotomy is vexing.

The 0.9x is almost certainly from WWII using a different baseline for 1" of armour plate, as previously mentioned. The 0.7x is most likely from sloping (as you surmised). 4e seems to have given up trying to allow for sloping, which given how variable the amount of vehicles was, and how variable its effect could be is arguably a wise choice.

[Rupert]

Originally Posted by Fred Brackin

So the Cheap metal TL6 armor is something available at TL 4. My guesses are that TL6 armor materials are iron plate for Cheap, mild steel for Standard, RHA for Expensive and a generic Really Good Steel Armor for Advanced.

1" thick steel plate weighs close to 40 pounds per square foot, so at Dr70/inch for RHA that's closest to 'Standard' metal at TL6 in VE2, which would also include non-hardend high-tensile steels when used appropriately. 'Cheap' would be mild steel.

This does mean that there's no metal armour worse than mild steel available in VE2 at TL4 and TL5, which doesn't seem quite right, but that's water under the bridge at this point.

[lugaid]

Originally Posted by Fred Brackin

You may be looking only at TL6. If you look at the tL6 column in Ve2 you'll see 4 types of metal armor labelled generically "Cheap, Standard, Expensive and Advanced".

It is not until you look at lower TLs that you see that what was "Cheap" at TL 6 was "Expensive" at TL4 and "Standard" at TL5.

So the Cheap metal TL6 armor is something available at TL 4. My guesses are that TL6 armor materials are iron plate for Cheap, mild steel for Standard, RHA for Expensive and a generic Really Good Steel Armor for Advanced.

From memory the WWII devs set TL6 Cheap Metal to be RHA and the three higher grades as progressivly better grades of improved steel armor and figured DR from that. You'll see that they set Cheap armor to be DR 70 per inch.

So WWII not only differs on what is RHA but it differs in the scale of how fine the level of distinctions are that it's trying to use.

No, I think that WWII has simplified things quite a bit more than that. Armor is given as a simple weight per point (with one point being one point on one of the six sides, so multiply that number by six to get the VE equivalent) for each of the various chassis sizes. So, a Medium Tank, with a surface area (SA) of 250, has a listed Armor weight of 21 lbs. per point. That is equivalent to a VE rating of 0.5 (250 sq. ft. × 0.5 = 125 lbs. per 6 points, or 1 point on each of 6 sides, is the same as 125 / 6 ~= 21 lbs. per point, rounded off). Motive subassemblies are given a separate line for each type of chassis, with their own SA and a base armor weight derived from the typical value (a Medium Tank has tracks with a base DR of 40, for example). Each Tank Chassis also has an option for "Expensive Armor", with a Medium Tank (as the continuing example) listed as 17 lbs. and the cost increasing ×2.75, as well as various armor slope options (which only affect F armor; this will become important in a moment).

This also means that different types of chassis are using different VE values, for instance Ship Chassis seems to be using an armor weight value of 0.6, since all of the Ship Chassis armor weights are just the SA divided by 10 (except the Raft, which is the SA divided by 100, implying a 0.06 armor weight value, which seems like that might be a typo and the value should match the other chassis on that table, giving it a weight of 7.5 lbs. per point). So it seems like they simply chose the type of armor used for that sort of vehicle in advance.

Another example: the Small Tank has a SA of 170 and an armor weight of 14 lbs., while the Small Wheeled Chassis, also SA 170, has an armor weight of 20 lbs. That would seem to indicate that the Wheeled Chassis vehicles use a cheaper form of armor than the Tank Chassis vehicles (which follows, as the Small Tank Chassis armor costs 4.5× as much as the Small Wheeled Chassis).

It seems that there was some considerable adjustment after the earlier playtest materials you are describing. In any case, the numbers match up well with VE, so if RHA is DR70 per inch in both 3E and 4E, then the armor numbers should stay consistent between the two editions as well. But, as noted, they do not. They seem to be altered by a consistent factor, though, at least within any given individual vehicle. If they've stopped accounting for slope, as I speculated earlier and Rupert seems to agree, that might explain the different factors, except that the slope on the M1A1 is only applied to the F facing, while the different factor is applied to all of the armor on the M1A1 in High-Tech. I suppose that might be an erratum that simply hasn't been noticed until now?

[lugaid]

And none of this explains why any adjustment was used at all. Why is the High-Tech PzIV rated at DR280 on the front, where the WWII PzIV is rated DR315, if they are using the same factors of DR70 per inch?

[Fred Brackin]

Originally Posted by lugaid

. In any case, the numbers match up well with VE, so if RHA is DR70 per inch in both 3E and 4E,

That 25mm of RHA equals DR 70 has been the rule in Gurps since High tech 1e. That you can be sure of.

That this is the Cheap armor in WWII is a problem. It's not the Cheap metal armor for TL6 in Ve2. That is something available at TL4.

Slope is accounted for in 4e as simply being a greater weight of armor. Sloping your vehicle armor increases your surface area. I'm pretty sure that David Pulver thinks it all comes out simpler that way.

All this is _much_ simpler in Spaceships as that is a system based on weight alone. Probably a sort of "average" density and shape is assumed for all designs.

[Fred Brackin]

Originally Posted by lugaid

And none of this explains why any adjustment was used at all. Why is the High-Tech PzIV rated at DR280 on the front, where the WWII PzIV is rated DR315, if they are using the same factors of DR70 per inch?

The one in HT gets its' DR from how difficult it was to penetrate with that difficullty being measured in an equivalent to milimeters of RHA (which is a common standard used in these things to my understanding).

I do not know much of "why" they did things the way they did things in WWII but I very much doubt they assumed the Panzer IV used Cheap armor. I suspect they took an average thickness of the Frontal armor and derived a DR based on which armor quality level they thought represented what the Panzer IV used in the real world.