Vehicles: 3E vs. 4E

[lugaid]

I have been constructing a dieselpunk setting (inspired by some anime, Gear Krieg, Crimson Skies, and other stuff that makes me happy). I wanted to get some solid vehicle designs, and since I feel really uncomfortable just making numbers up I wanted to create them using GURPS WWII and GURPS Weird War II, which have simplified vehicle design sequences that include diesel powered mecha and such things. All well and good.

Now, I know that there are some different assumptions between 3E and 4E on the matter of rating vehicles, especially in numbers that are not real-world based (examples of real-world based numbers include speed and weight). DR, particularly, varies somewhat between the two editions. I figured, though, that I could look at some of the vehicles that have been converted and work with estimates based on how those differ. Unfortunately for me, there are two vehicles that make a perfect comparison, but I can't for the life of me figure out why they were converted as they are. Those two are the M4A1 and the Panzer IV. Each is described in GURPS WWII, and each is described in High-Tech for 4E.

Mostly, the differences make some sense. There are some arbitrary elements and changes, which I can work with (top speed in both cases is dropped from a nominal 14 that would be implied by a simple conversion to 12 for some reason, for example, but that's not a huge issue), but the problem area is DR. The Panzer IV DR can be approximated by taking 90% of the WWII DR for both Front and Sides/Back and rounding down to the nearest 10. Those numbers work out. The M4A1, though, is almost exactly taking 70%, with no need to round the numbers. I can't for the life of me figure out the rationale for why one is 90% and the other 70%. Does it have to do with the fact that the M4A1 is given armor slope in WWII, perhaps? In which case, I'm not sure what the rationale behind that is, as armor slope should have some positive effect, right? Or is there some new study that has overturned previous thinking on the matter?

[Fred Brackin]

Originally Posted by lugaid

I wanted to create them using GURPS WWII and GURPS Weird War II, which have simplified vehicle design sequences that include diesel powered mecha and such things. All well and good.

Now, I know that there are some different assumptions between 3E and 4E

Your problem may not be where you think it was. In both 3e and 4e 25mm of RHA equals DR70. The exception was/is the WWII line which was non-compatible with the rest of Gurps from its' beginning on the subject of DR.

I can assure you that nothing was "converted" from the WWII statistics. The 4e stats in HT will have been based on real world numbers and the 25m RHA standard.

I can not tell you how to convert WWII line stats to general Gurps either. I think (but am not sure) that the WWII vehicles ended up over-armored by fiddling the DR tables to compensate for some of the tank guns overperfoming.

You will find my name as a playtester in the WWII coreboook. All I can say is that the playtest was rushed and I missed what they did to the DR table. Tanks have never been my thing anyway.

[Polydamas]

Yes, GURPS World War II defined vehicle DR differently than the other GURPS serieses to better represent WW II vehicle combat.

Its also likely that the people who wrote those different books used different references for the real-world properties of vehicles. Because its hard to go out and just weigh a tank, and because one factory in February 1945 built a vehicle differently than another factory in November 1942, there are many slightly different numbers floating around.

[lugaid]

Originally Posted by Fred Brackin

Your problem may not be where you think it was. In both 3e and 4e 25mm of RHA equals DR70. The exception was/is the WWII line which was non-compatible with the rest of Gurps from its' beginning on the subject of DR.

I can assure you that nothing was "converted" from the WWII statistics. The 4e stats in HT will have been based on real world numbers and the 25m RHA standard.

I can not tell you how to convert WWII line stats to general Gurps either. I think (but am not sure) that the WWII vehicles ended up over-armored by fiddling the DR tables to compensate for some of the tank guns overperfoming.

You will find my name as a playtester in the WWII coreboook. All I can say is that the playtest was rushed and I missed what they did to the DR table. Tanks have never been my thing anyway.

That's interesting. Starting with machine guns, a Browning M2HB does 13d+1 in WWII, while in High-Tech it does a similar 7d×2 pi+. More interestingly, the 75mm Short Tank Gun in WWII, which is used by the Panzer IV, does 6d×5 (2) + 3d [6d] and the equivalent, more specific gun in High-Tech, the Rheinmetall KwK40 75mm×495R, does 6d×10(2) pi++ with a follow-up of 6d [4d-1] cr ex. The follow-up in each case is due to different methods of determining explosion damage, of course, but the rest doesn't look like overperformance in WWII to me.

In any case, do you think that I should just re-figure the armor design numbers using 3E Vehicles, then? WWII provides a Surface Area stat for its chassis types, so that would make it pretty easy to go to Vehicles for that, if Vehicles uses the standard assumptions. After that, it should be pretty easy to just fudge up some numbers for guns based on what is in High-Tech (I didn't mention, but this setting is intended to be a subcreation type world, not one set in our own history and geography, so I have a lot of freedom in that area, and I'm more comfortable with fudging weapon numbers than I am vehicle numbers, especially for counter-historical vehicles like diesel walkers), so that's not really an issue.

[lugaid]

Originally Posted by Polydamas

Its also likely that the people who wrote those different books used different references for the real-world properties of vehicles. Because its hard to go out and just weigh a tank, and because one factory in February 1945 built a vehicle differently than another factory in November 1942, there are many slightly different numbers floating around.

As noted, the real-world numbers are at least in the same ballpark between the WWII ones and those in High-Tech, so I am really less concerned with those than the game statistic numbers (DR, SR, and so forth). Do you think that adjusting the WWII numbers to match more closely with Vehicles is a good idea?

[Rupert]

Originally Posted by lugaid

That's interesting. Starting with machine guns, a Browning M2HB does 13d+1 in WWII, while in High-Tech it does a similar 7d×2 pi+. More interestingly, the 75mm Short Tank Gun in WWII, which is used by the Panzer IV, does 6d×5 (2) + 3d [6d] and the equivalent, more specific gun in High-Tech, the Rheinmetall KwK40 75mm×495R, does 6d×10(2) pi++ with a follow-up of 6d [4d-1] cr ex. The follow-up in each case is due to different methods of determining explosion damage, of course, but the rest doesn't look like overperformance in WWII to me.

That's because the gun on the PzIV listed in 4e's HT is not the short 75mm listed in WWII. It is instead a quite powerful long-barrelled gun intended for killing tanks. The original short 75mm gun was intended to provide fire-support for infantry.

[lugaid]

Originally Posted by Rupert

That's because the gun on the PzIV listed in 4e's HT is not the short 75mm listed in WWII. It is instead a quite powerful long-barrelled gun intended for killing tanks. The original short 75mm gun was intended to provide fire-support for infantry.

You're right, I misread the WWII data. It should be WWII's 75mm Long, which is 5d×11 (2) + 3d [6d]. The 75mm Short is supposed to represent the KwK37.

EDIT: Which means that the damage is within 10% in both books.

[Fred Brackin]

Originally Posted by lugaid

You're right, I misread the WWII data. It should be WWII's 75mm Long, which is 5d×11 (2) + 3d [6d]. The 75mm Short is supposed to represent the KwK37.

EDIT: Which means that the damage is within 10% in both books.

Not necessarily. I think the big offender was the Sherman's notoriously anemic original gun. German tank guns were the standard the US was trying to upgrade to.

[lugaid]

Originally Posted by Fred Brackin

Not necessarily. I think the big offender was the Sherman's notoriously anemic original gun. German tank guns were the standard the US was trying to upgrade to.

The Sherman II is llisted as carrying the 75mm Medium, which is supposed to represent "the US 75mm M-2, M-3, M-6, and M-17", then notes a later variant as carrying the 75mm Long, which WWII describes as being equivalent to the US 76.2mm M-1 AA Gun and the M-5 AT Gun (which seems to be what High-Tech lists and sets for the M4A1(76)W Sherman IIA, as the Watervliet 76.2×539mmR M-1). So, the guns do damage that looks very similar between editions.

[Rupert]

Originally Posted by Fred Brackin

Not necessarily. I think the big offender was the Sherman's notoriously anemic original gun. German tank guns were the standard the US was trying to upgrade to.

It was a perfectly fine gun for its time and intended role (mid-war, infantry support with a side-line in tank killing). It's just that post D-Day wasn't mid-war, and tanks that aren't great at killing other tanks tend to have unhappy users.