I'm outfitting a Dominator-class Cruiser and I'm curious as to how useful certain Components will be for an assault ship. While the Invasion Bridge, BG-15 Assault Scanners, Barracks, and Drop Pod Launch Bays are all obvious in how useful they will be, there are a few others that leave me wondering.

Nova Cannon: The ship comes with this, so it's going to be there. It seems like it will be great for punching holes in orbital defenses (and possibly minefields) from a standoff distance. However, I am wondering if this is also useful for direct bombardment of ground targets. I have never heard of weapons other than Macrobatteries and Lances used for orbital bombardment, so is it even possible to bombard with a Nova Cannon?

Disruption Macrocannon Broadsides: Is there some reason that these could not be used to bombard? I like the idea of knocking power out over a large swath of ground - hitting hive cities, ground-based defense weapons, etc. so that they can be captured relatively intact by the troops the ship is dropping.

Torpedoes: This ship will not be mounting Torpedoes, but otherwise this is the same question as with the Nova Cannon - can Torpedoes be used to bombard ground targets?

I'm pretty sure that whatever you fire that Nova Cannon at will disintegrate. I refer to http://forums.tauonline.org/40k-universe/49706-nova-cannon-firepower-calculation.html] for calculation on this kind of thing. It is really stupidly powerful. I recommend reading the thread to see for yourself, but they really are immensely powerful.

A macrocannon should be able to bombard pretty much everything, so I don't see this as a problem. Possibly the payload goes off upon atmospheric entry, but it'll still spread nastiness upon the area, considering the size. I refer to this:

Aight, it was a bit hard to read, but right-click and show the whole image for a better idea of it all.

So yes, bombarment should not be an issue.

I wasn't sure if the shell of the Nova Cannon - which in RT we all know is an explosive charge (with an explosive radius of 10,000 km in space!) and not a high-density penetrator - would be able to survive atmospheric interface. I read the link you sent, and the calculations are absurd. They try to strictly apply physics at some points and totally ignore them at others. Far better I think to use the same level of "fuzzy physics" on both sides.

So, if a Nova Cannon was used in atmosphere, what would be a reasonable area for the explosion to cover?

As for the disruption macrocannons, they don't fire solid shells but instead charged packets of energy. Again I'm wondering if these will survive atmospheric interface well enough to be used to bombard ground targets. I don't really see why not, but I've never heard of such weapons used for these purposes in WH40K before.

Cryhavok said:

Considering that a macrocannon shell can take out way more than a single vehicle - covering a vast area in ruin, I'd think that a barrage of disruption cannons could leave behind a battlefield where nothing electronic was left operating much like a sci-fi version of directed EMPs. The power could be restored after some time (likely requiring at least 30 minutes of work if the starship combat rules have anything to say about it), but the defenders might not get that long to spend tinkering with the gear if the drop pods are coming down on them! Captured gear can be better than destroyed gear!

And, as for the ship type, it's going to be a Dominator. It's not ideal, but it's what's there, so the Nova Cannon and Armoured Prow are set in stone for this one and it's going to have macrocannon broadsides but I'm considering Disruption Macrocannons over Grav-Culverins for this purpose.

Cryhavok said:

Makes some sense, but I'm not sure how to work out what gets directly hit by orbital bombardment. I always took it to be more of an area saturation thing than pin-pointing targets. Lances can pin-point target, but not against things smaller than titans/superheavy tanks.

Mostly though, what gets directly hit is gms call on how they want to handle it. You could just as well hit things directly at the need of the story.

Cryhavok said:

The rule you are quoting is for a single "battery" attack not a single weapon. That being said I would rule that within the affected area all power grids and electrical based systems would be effectively knocked out unless it was specifically shielded (Like most military kit is!). Individuals within the affected area would be as if attacked by a Haywire grenade. The reason for this is exactly as the OP intended: Large scale power systems would be more seriously affected than individuals. Of course one must remember that Major cities usually have Void shields that can shrug off a cruiser's bombardment. Additionally, They can usually shoot back with a powerful array of ground based Lance batteries, Torpedoes and other nastiness!

Radwraith said:

I very much doubt that a Leman Russ would count as shielded against such surges if a Lunar-class Cruiser is not. I don't see much evidence that any Imperial tech has such specific protections.

When firing a Nova Cannon at a target on a planetary surface, how would a "shot goes long" result work? Would the shell be destroyed by impact with the planet before it could detonate?

About disruption weapons: so you would have them shoot at a one kilometer long ship and only take out a small number of systems, but when shot at a planet whipe out every electrical system within ten kilometers? How does that work?

Cryhavok said:

Not every system, but they would still do damage like macrobattery bombardment, but only to armour/mechanised infantry/power armoured infantry/aircraft units and fixed defenses in the 10 km square. The damage done would be temporary, as the systems could later be restored. If the unit that's been disrupted is 'destroyed' then it's possible that their assets could be captured relatively intact and repurposed by whoever claims the battlefield.

I would also say that it's likely that any starship has FAR more shielding from such disruptions than any land-based mobile unit (although fortresses and other fixed defenses are much more likely to be protected like very large starships).

The other potential problem I can see with using Disruption Cannon for orbital bombardment is you're going to leave a really cruddy ground-to-orbit vox reception, so spotting for correction of shots is going to be problematic, but if you're using it as a technic area-denial weapon then odds are you're not necessarily too bothered about using ground-based forward observers (well, you might be if follow-up shots are from other weapons systems).
Also, it'd only be a problem for vox links if you're shooting through an atmosphere, so airless worlds and/or psychic communication would not be bothered by a sudden large ionized mass of air above them.

And while the RAW* say you can't bombard with torpedoes (as yet, anyway), in fluff, and Battlefleet Gothic, you can. Hell, that's one reason you use ground observers, to guide in projectiles capable of course correction and terminal guidance (and anti-starship torpedoes make some of the best bunker-busters out there).

*I could be wrong, I don't have my copy of BfK for reference just now; it might just ban virus warheads on orbital bombardment torps. I believe the rationale was explicitly to prevent players from getting their hands on exterminatus grade weaponry.