using spaceships for battletech-style tactical mecha combat

[Fred Brackin]

Originally Posted by ericthered

ehh, its less of canon and more of a rule of thumb t

HE shells are only 10% Explosive? that's news to me. I had thought they had substantially more of their weight as explosive. Huh, the things you learn.

<smiles and waves as departure for House rule land begins>

Aerial bombs and even mortar bombs can hit 50% filler and tht might be around the practical mimum for effective fragmentation but for artillery there very high firing stresses.

Also specialty items such as the MOAB thermobaric bomb neither do fragmention nor being shot out off a gun and they can be 90% but a MOAB is more like a single use vehicle than a bomb.

[johndallman]

Originally Posted by Fred Brackin

Perhaps you were trying to say that battleships (and quite possibly all battleships everywhere) were armored in a better grade of steel than RHA. If so I believe the burden of proof is upon you. Specifically I believe you will need to document all of the thickness of the armor belt, the material of that belt and the degree to which it was superior to RHA.

RHA is a useful standard of comparison, and is used for mass-produced armoured vehicles. Battleships had specialised kinds of armour steel for some parts of their armour.

The belt, the turret face-plates, and other components that were liable to be hit directly by armour-piercing shells had face-hardened armour, which was lighter than RHA for the same degree of protection. The difference wasn't huge, but battleships were weight-critical, especially after various treaties limited their tonnage.

The decks and other parts liable to glancing hits had armour that was similar to RHA, but every manufacturer had their own tweaks and improvements.

RHA, Harvey armour, Krupp armour, and Krupp cemented armour.

[Anthony]

Originally Posted by ericthered

ehh, its less of canon and more of a rule of thumb

No, it's actually the standard created somewhere around 1990 back in GURPS 3rd edition: DR 70 is defined as 1" RHAe.

Originally Posted by ericthered

HE shells are only 10% Explosive? that's news to me. I had thought they had substantially more of their weight as explosive. Huh, the things you learn.

Bombs and missiles can be a higher percentage, but for guns it simply isn't practical to go much over 10% because explosives are much much lighter than metal.

[ericthered]

Originally Posted by Anthony

No, it's actually the standard created somewhere around 1990 back in GURPS 3rd edition: DR 70 is defined as 1" RHAe.

Haven't damage numbers, especially for firearms, changed in the 3e-> 4e transition?

(I don't own 3e core. I'll sometimes get 3e books that cover topics generically, as so many of them do)

[Fred Brackin]

Originally Posted by ericthered

Haven't damage numbers, especially for firearms, changed in the 3e-> 4e transition?

(I don't own 3e core. I'll sometimes get 3e books that cover topics generically, as so many of them do)

The actual establishment of RHA came in the first edition of High Tech which was slightly before the change to 3e. Indeed it may have been the major reason for the change.

As to to gun damage figures the basic answer is no. 2D for .45 ACP and 2D+2 for 9mm and 5D for 5.56mm and 7D for 7.62mm goes back to that High Tech 1e and is unchanged in the more than 30 years since then. You had some different numbers in products before that change but we're talking things like the 1st editions of Space and Autoduel. That's all 1e/2e v. 3e. Not 3e v 4e.

[Varyon]

Originally Posted by ericthered

I do mean to dispute that number, because I find it frequently gives underwhelming results, especially for things that ought to be bouncing rather impressive attacks.

I think there are two factors in play in GURPS that make 1" RHA = DR 70 = 20d potentially underwhelming. On the smaller scale, it's that ST-based damage is well out of line for such a scheme (while the wounding on an unarmored person may not be far from reality, the armor penetration is typically excessive). More generally, given the variability inherent in rolling for damage, and that DR is set at roughly the average result of such rolls, it's not uncommon to have an attack penetrate armor that is "proof" against it. The optional Armor As Dice rule (canonized in Pyramid #3/34's "Armor Revisited" article) largely solves the latter issue (for the former, you'd probably need to apply a poor armor divisor to muscle-powered weapons).

Originally Posted by ericthered

HE shells are only 10% Explosive? that's news to me. I had thought they had substantially more of their weight as explosive. Huh, the things you learn.

Looking at the description of explosive shells in High Tech (starting on p169 for those following from home), HE points back to LE, which states the shells are typically 15% or more explosive filler (no upper cap is given). The 10% figure seems to match more with SAPHE - this again points back to SAPLE, which states the shells are typically less than 10% explosive filler. The difference between HE and SAPHE, in GURPS terms, is that the former has AD (0.5), while the latter has no Armor Divisor; against an armored target, HE is entirely reliant on the explosive to do anything, while SAPHE may be able to penetrate the outer hull, causing massive structural damage by detonating inside the target. I don't know which category the shells you're discussing actually fell into, however.

[Varyon]

Originally Posted by ericthered

A while back I did an analysis of spaceships armor and came to the conclusion that the values were about a third of what they should be to be competitive with human armors.

Honestly, it's probably most appropriate to compare the Spaceships armors with those produced by the Armor Design articles from Pyramid (Pyramids #3/52, 85 and 96). We'll go with your suggestion of one SM+0 unstreamlined armor system being equivalent to torso armor, so 10 lb spread out over 7 sf; the articles explicitly state vehicle armor would typically be Solid, so we'll go with that. DR by the Spaceships scheme is equal to the dDR at SM+6 (that is, SM+0 has 1/10th the DR of SM+6), and the armor is 1/1000th the cost. The relevant equation for the armor design is DR = 10/(7*W), while the cost is 10x the cost per lb (Solid gives a multiplier of 1 for weight and cost alike).

So, Steel vs RHA. SS Steel armor is DR 2 and $20. RHA is DR 2.5 and $30. That's extremely close. You can make the RHA better by making it Plate construction, although it's arguable if that would make a difference at Spaceships scales (it almost certainly would at mecha scales, however, so is important to keep in mind). That increases DR to 3, for your x1.5 multiplier, but also increases cost to $150. There are also other steels available, at higher cost for better performance - still using Solid construction, Hard Steel (TL 6, like RHA) gives DR 2.85 (and $35), for example.

Next, Light Alloy vs High-Strength Aluminum. SS Light Alloy is DR 3 and $50. High-Strength Aluminum is DR 3.5 and $120. Again, close (the pricing is quite different, although the latter drops to only $60 at TL 9+). Plate construction, or a more expensive alloy (Titanium alloy) can again increase DR for a higher cost.

For the last High-Tech material, we have Metallic Laminate vs Titanium Composite. SS Metallic Laminate is DR 5 and $100. Titanium Composite is DR 7 and $2500. That's more of a jump - +1 SSR rather than ~+0.5 SSR - but also a massive price hike (although the latter, again, drops at TL 9+, this time to $250, but that's still a much higher jump than we've been seeing). Perhaps the version in SS uses aluminum instead of titanium?

Getting into Ultra-tech, we have Advanced Metallic Laminate vs Titanium Nanocomposite, which works out to DR 7 and $200 vs DR 12 and $25,000 ($600 at TL 10+). That's roughly +1.5 SSR, or x1.7, to performance, but again a massive price spike.

For Nanocomposite vs Advanced Polymer Nanocomposite, we're looking at DR 10 and $500 vs DR 18 and $500 ($250 at TL 11+). For Diamondoid vs Diamondoid, we're looking at DR 15 and $1000 vs DR 24 and $500 ($250 at TL 12). For Exotic Laminate vs Hyperdense, we're looking at DR 20 and $2000 vs DR 36 and $500. These are all around the same DR difference as Advanced Metallic Laminate vs Titanium Nanocomposite above, although the prices certainly don't follow the previous patterns (largely because this article went with UT's scheme of keeping the same price while boosting performance as TL goes up).

Rewinding, Iron vs Good Iron is about the only data point we have for Low-Tech. That works out to DR 1.5 and $60 (only $12 at TL 5+) vs DR 2.5 and $250 (only $50 at TL 5+), which is more in line with the Ultra-Tech armors above. Of course, using Cheap Iron drops that part to DR 1.8 and $150 (only $30 at TL 5+), which is more in line with the High-Tech armors.


Given all that, my typical inclination would be to use the Armor Design articles for everything - humans, cars, mecha, spaceships, etc - when possible, but keeping in mind Spaceships is pretty close to accurate pre-TL 9, provided you use the cheap stuff. Note that, rather than needing to calculate square footage, you can just calculate the SM+0 coverage as above and apply +1 SSR to DR and +3 SSR (x3, x10, etc) to cost per +1 to SM. For example, if you want Titanium Nanocomposite Plate available for your SM+5 (by weight) mecha, each 10-lb system at SM+0 would give DR 15 and cost $12,500 ($3000 at TL 10+). At SM+5, this is instead DR 100 (dDR 10) and $12.5M ($3M at TL 10+).

[ericthered]

Originally Posted by Fred Brackin

The actual establishment of RHA came in the first edition of High Tech which was slightly before the change to 3e. Indeed it may have been the major reason for the change.

As to to gun damage figures the basic answer is no. 2D for .45 ACP and 2D+2 for 9mm and 5D for 5.56mm and 7D for 7.62mm goes back to that High Tech 1e and is unchanged in the more than 30 years since then. You had some different numbers in products before that change but we're talking things like the 1st editions of Space and Autoduel. That's all 1e/2e v. 3e. Not 3e v 4e.

Does that mean I can stat up that 12-inch naval cannon with the rules in vehicle design for weapon design and it will be comparatively authoritative?

[Fred Brackin]

Originally Posted by ericthered

Does that mean I can stat up that 12-inch naval cannon with the rules in vehicle design for weapon design and it will be comparatively authoritative?

Are you referring to the weapon design rules in Ve2? Those will give you basically accurate figures for KE damage either for 3e or 4e. Explosive damage (but probably not HEAT) would need to be refigured for 4e. That did change. ACC is vary different for 4e. Range was always a little problematic for Ve2 when dealing with large indirect fire weapons.

To convert general explosive damage divide the 3e dice by 12 and that gives you effective pounds of TNT. Take that number and get the square root of it. Then multiply by 12 and you've got 4e dice of damage.

[Rupert]

Originally Posted by ericthered

I believe battleships do have a fair record of bouncing hits from inferior foes, including the last generation of battleships and the main belts a good record of bouncing hits from other battleships. . Jutland had 25 ships go down, including 4 battlecruisers and 4 other large ships, but not a single battleship went down on either side. The Battle of Denmark strait had a not dissimilar result, with the battlecruiser getting sunk, but neither battleship actually getting through the armor belts: hits were to other areas.

HMS Hood was mostly likely sunk from a shell penetrating a non-belt and non-main deck armour area too. Also, for what it's worth, her deck armour wasn't actually that much worse than Bismarck's.

I don't have Doug's sheet (I need to get my hands on it one of these days), but when I crunched the numbers in high tech a while back the higher-velocity weapons generally did their dice of damage equal to their caliber in mm. A 12 inch/ 30 cm shell in high tech with the high velocity guns should do around 300d of damage. 150d(2) is enough to get through the armor without much fuss.

When using VE2 to design big guns, they ended up having roughly correct penetration for their 1/2D damage, and GURPS 3e said all indirect fire counted as being at 1/2D range, so that worked out okay.

I'm also a bit worried about the armor being able to take the explosive force of a shell. 785 DR can resist about 225d of damage, that's around 220 lbs of RDX via the numbers in high-tech -- a quarter of the historical weight of a 12-inch shell.

An AP shell usually had about 2-3% of its weight as HE filler (the US 16" gun's massive 2700 pound AP shell that people tend to gush about had all of 41 pounds of filler - 1.5%). The highest amount of filler I found with a quick search was in the HE shells for the Mark II 15-inch gun used by the RN in both world wars. It had about 220 pounds of HE, and was only used in WWI (the WWII HE shell had about 130 lbs, like the WWI semi-AP shell for that gun). The high-capacity HE shells for the US 16" guns used in WWII and later for shore bombardment had about 154 pounds of filler in a 1900 pound shell (so ~8%). Most large navel shells of the time used TNT or some other HE fillers with similar or slightly higher REF.

Thus the largest HE attack from a shell that a ship would likely face would be about 6dx30 cr ex, and most would have about 6dx20 cr ex. The armoured belt of a battleship would stop that, and even the 'all or nothing' armour of USS Nevada had enough heavy (though unarmoured) decks to set off an HE shell before it reached the main armoured deck, which would easily stop damage from an HE shell exploding 1-2 decks above it. The WWI-era mutli-layered decks of battleships would also easily defeat such shells.

What HE shell could do, and which the RN was planning to use them for (hence their use of semi-AP shells) was smash up the lightly or unarmoured upperworks of battleships, wrecking secondary batteries and fire control and setting fires.