Everything else potentially carried by an Imperial Navy vessel is already covered, so I thought I'd try my hand at providing rules for the other weapon seen mounted beneath the armoured prows of Imperial Navy Cruisers...

"A Nova Cannon is a huge weapon, normally mounted in the prow of a ship so that the recoil it generates can be compensated for by the ship's engines. It fires a projectile at incredible velocity, using graviometric impellers to accelerate it to close to light speed. The projectile implodes at a preset distance after firing, unleashing a force more potent than a dozen plasma bombs."

To fire a Nova Cannon, nominate a point anywhere between 4 and 18 VU within the ship's prow arc. The weapon generates a blast wave several thousand kilometres across, and may catch several ships within its effect if carefully aimed. Nova Cannons are extremely powerful weapons, easily able to wreak vast destruction upon enemy vessels at great range, but are inaccurate. A Nova Cannon may not fire if any Manoeuvre Actions have been performed which required a Pilot (Starship) test with a difficulty of worse than Challenging (+0), or if the ship is Crippled.

Roll to hit, applying a modifier based on the distance to the target point. If the target is within 6 VU, you take a -10 penalty. If the target is between 6 and 9 VU away, you take a -20 penalty. If the target is more than 9 VU away, you take a -30 penalty.

A successful roll scores a single hit against every ship within half a Void Unit of the target point (in most cases, ships will not be close enough together to hit more than one at a time). If three or more degrees of success were scored, a direct hit has occurred, and a single one of those ships suffers 1d5 hits instead. Hits from a Nova Cannon deal 2d10+4 damage ignoring armour. Void Shields apply normally to hits caused by a Nova Cannon. The Nova Cannon has a Crit Rating of 5, and will only deal a single Critical Hit at most, no matter how many ships are struck (the ship hit multiple times will suffer the critical hit)

A Nova Cannon may only be fitted onto a Cruiser or larger vessel with an Armoured Prow - the massive superstructure of the Imperial Navy's signature prows are perfectly suited to withstanding the heavy recoil of a Nova Cannon firing. It uses 15 power and takes up 10 space, including a dedicated magazine (which will, if the Nova Cannon is damaged, explode in the same manner as a Munitorium, described on page 205 of the Rogue Trader rulebook). The entire Nova Cannon costs 5 SP.

I would add some rules for firing the Nova Cannon when the ship has suffered structural damage. Something on the lines of "If the ship has suffered X damage, roll Y when the Nova Cannon fires" as the massive recoil causes further stress to the ships superstructure.

Just my 2 cents, since I have already printed out your rules and tucked them into my RT book. Great piece of work!

-Cynr

Cynr said:

Covered, to an extent; in BFG, Nova Cannons can't be fired when the ship is crippled. I did essentially the same thing for these rules - a crippled ship can't use its Nova Cannon.

I might add a bit about what happens if you damage the Nova Cannon itself (representing damage to the superstructure supporting it as much as damage to the weapon itself), but these were very much a rough-and-ready translation of the BFG rules, so are invariably in need of a little more fleshing out and fine-tuning.

Nice. I'm printing it out right now.

What about the "Inferno Cannon"? I'm reading the rules on them right now and unless someone beats me to it, I'll post my interpretation right here.

I never understood why a Nova cannon fires at such a high velocity when it doesn't rely on kinetic damage from its speed but explodes instead.

Gribble_the_Munchkin said:

In theory, as a fairly inaccurate weapon anyway, you want the large explosive payload to be amongst your enemy as swiftly as possible - if the shell is too slow, the enemy has time to move away from it (plus, if it's fast and you do manage a direct hit, that's a massive impact followed shortly by an immense explosive - extremely effective).

Maxim C. Gatling said:

Never mind! The "Inferno Cannon" was the Space Fleet version of the Nova Cannon.

You have really toned down the blast radius.

Also it should scatter on a miss.

The range is also too short, in BFG they could reach WAY out there. 5x as far as a standard macrobattery. (which poses a problem with the limited detection ranges presented in RT.

They should also have the recharge trait. (IE in BFG you had to do a reload ordinance special order to fire it again) Or perhaps you could have the players need to make a command roll to fire it again the next turn, with failure meaning it took longer to reload and you need to wait a turn to use it.

llsoth said:

No, I haven't. Anything within the same Void Unit covers an area 10,000km across. That's actually much larger than their blast radius in BFG (it's an area roughly equivalent to a 5cm radius circle in BFG terms; the Nova Cannon template is about half that radius), so I went for half a VU instead. Thing is, without requiring a map, this kind of thing is not easy to represent.

llsoth said:

Again, not easy to represent when your basic unit of measurement is an abstract unit equivalent to approximately 10,000km and you're trying to avoid requiring a map.

llsoth said:

In BFG, it's got a range of 150cm - that's about 150,000km, or about 15 VUs. I've been working with a x1.2 adjustment on BFG-RT distance conversions since I wrote that, so that ends up as 18 VUs instead.

llsoth said:

Remember that a turn in RT starship combat represents about half an hour of time, while BFG turns can represent as little as 15 minutes (according to Andy Chambers, who wrote BFG).

But, considering that I wrote these in about 5 minutes on a whim, that they're a first draft with no testing of any kind, within 24 hours of obtaining the Rogue Trader rulebook and without having completely read the starship rules, I fully accept that they need a lot of work. I never claimed that they were the perfect, definitive example of the rules for the Nova Cannon. If you think you can do better, feel free to make the attempt.

With regard to ranges, on page 213 it states that 1 VU = 1 inch in playing tabletop like BFG

So you have cut the blast radius in about half.

There are rules for scatter in both BFG and in Dark Heresy/Rogue Trader I don't see why they would not work. Even if there is no map you have to know where the other ships are.

Wow if a 150cm from BFG = 15 VU do the normal 30cm macrobatteries only reach out 3 VU? A better rule of thumb is to dive it by 2 (yes I know 1cm =.39 inches but I am going with easy and simple).

Thus the macrobatteries from a BFG lunar Cruiser would shoot 15 VU max which compares nicely to the rogue trader figures of 12 for mars and 18 for sunsears. A better max range for a Nova Cannon in Rogue Trader would be 75 or say 32 in the stats block.

While it is true that the turns are longer... the ratio should still be preserved. Because the turns are twice as long do the guns get to shoot twice per turn? Nope it has been abstracted out with a single firing actually representing many salvos. The fact that it took a long time to reload a nova cannon (required a reload ordinance roll) was a draw back to the weapon, which if you take out will make it more powerful in relation to other guns. As an ordinance weapon it is much harder to abstract it out as firing it actually represents a single shell.

If you don't like them, go and write your own. Clearly you've got nothing but criticism for the five-minute rough work of another. Given that you've not actually seen the most recent version of them (which I'm not going to post in this thread at this point, because they're part of a larger work now and still being worked on), your criticism of a rough first draft is essentially meaningless.

llsoth said:

Which doesn't match up with the actual distances they're supposed to represent, nor with the supposed board scale used in BFG. Then again, neither do some of the starship weapons ranges - the Sunsear batteries are clearly meant to be those used by Sword-class Frigates, yet they have half as much again range, and the Sword is able to fit two such batteries, doubling their effective firepower compared to how they're represented in BFG.

llsoth said:

Only if you're considering the 'tabletop scale' suggested in the rulebook, which I wasn't. In BFG, the Nova Cannon template is about 5cm (approximately 5,000m, or 1/2 a VU across). Given how small a space starships take up, and the distances that tend to separate them during space combat, it felt more appropriate to keep the potential number of vessels affected low (as is generally the case in BFG).

llsoth said:

Yes, there are rules for scatter in both BFG and DH/RT (though, originally, the Nova Cannon was purely guess-range rather than scattering). However, none of those systems are dealing with a massive three-dimensional space tens of thousands of kilometres across. BFG quietly sidesteps the issue of three-dimensional combat, while DH and RT include scatter from the perspective of ground combat, where the distances are much smaller and gravity keeps scatter reasonably in-check.

llsoth said:

The BFG = RT conversion is inconsistent anyway, and can only be used as a rough guide at best. You don't like my decisions, tough. I didn't write these rules specifically to please you, I wrote them as a five minute task just to see if I could.

llsoth said:

As I said before, which you decided to willfully ignore before you continued to berate me, I wrote those about 24 hours after getting the RT book, without having read them cover-to-cover. I was, at the time, going by the values on the table, which gave no clue that they weren't maximum ranges. Ignoring the context the rules were written in does you no favours, and the fact that I wasn't fully versed in a new ruleset when I wrote them means that mistakes inevitably crept in.

As it stands, though, the Mars Macrocannon Broadside is the one of a Lunar-class Cruiser, at least as far as I can tell. More powerful ones would take up more space and use more power, which (when paired with a Titanforge Lance Battery) a Lunar-class can scarcely afford and still leave room for Torpedo tubes.

N0-1_H3r3 I was not berating you. I was posting a simple list of things you had changed from the BFG version that stuck out to me. Things I felt changed the role the nova cannon would play in a battle. I apologize if the tone sounded overly critical. As you no doubt know sometimes the intended tone of a message does not come across well when texting and on message boards.

That having been said, statements like "Given that you've not actually seen the most recent version of them (which I'm not going to post in this thread at this point, because they're part of a larger work now and still being worked on), your criticism of a rough first draft is essentially meaningless." and defenses such as, I did not read all the rules, makes me wonder if I should.

llsoth said:

I apologise for the tone of my previous post - I was in a particularly foul mood for a reason I now can't remember, and thus lashed out when I should've been more polite and receptive. Your post appeared rather blunt and critical in tone, but I am fully aware of the difficulties of forum-based communication (and normally acknowledge it, when in a more even mood than I was last time I posted on this thread), however, and understand that this likely wasn't your intent.

I've written up a fair list of custom starship components, which continues to expand, of which the Nova Cannon is one. For reasons I'm not going to go into detail with at this particular point in time (it's a complicated matter), I'm not going to be releasing that document in general, or an updated version of the Nova Cannon rules in particular, for the time being. There's a good reason for this, but one I'm not entirely willing to disclose at this point in time. I will say that I have considered the feedback given in this thread, however.

Again, apologies for my previous ill-mannered post.

No-1, I am big fan of your work! I have been using both the abhumie supplement and Tyranid one in my games and write-ups. Keep u with good work!

It's a bit of threadomancy, slightly, but I am indeed keen to see/hear of the updated NC rules. I'm currently looking at converting in my Demiurg ideas, so I'm keen to keep an ear to the ground/eye open for the works everyone else is up to.

More'n that, I thought folks might like to know that Aaron D-B's book Cadian Blood features a few firings of a Nova Cannon. Very well done too they are, well, at least I thought so. Doesn't help that much, but adds a bit of inspiration for going at the weapon perhaps slightly differently from the BFG rendering of events.

Xisor said:

When the opportunity arises, I'll make them (and various other bits and pieces) available... but I've become very busy of late working on things that I can't discuss, so the amount of time I'm willing and able to spare for my own projects has become significantly reduced. I'm still doing bits and pieces where I can spare the time and effort (such as releasing version IV of The Great Devourer in January, once the new Tyranid codex has been released for 40k - new species of creature are coming, so it would be lax of me not to add them in), but bigger things are afoot that are taking most of my attention at the moment...