I could a planet having dozens of grounds based macrocannons and some cities even having multiple void shields.

Perhaps a long lost planet that has Archeotech defenses...oh, we'll blast the capital, what you say, rounds didn't hit....whats that coming at us....AAAAAH....

The majority of the fluff I've run across reguarding orbital bombardment indicates that the primary inaccuracy comes from atmospheric effects messing with the auspex and targeters rather then with the munitions themselves. Its also worth noting that the guns in a weapons battery change greatly, from massive batteries with scores of Titan-sized weapons to just 3 or 4 Macrocannons launching bulding-sized explosive shells.

So depending on exactly what kind of batteries the ship has, your looking from dropping anything from semi-precice bombardment to wide area nuclear devistation, assuming no kind of defense.

The only thing that's safe to assume, imho, is that the numbers don't make sense.

For perspective, here's a diagram with the yield of US nuclear weapons compared to the 1,000,000 kg macrocannon projectile.

Am I the only one who thinks this looks a bit much? I'm all in favour of orbital bombardement but.... I'd kinda wanna see lances or actual nuclear weapons for that kind of destruction.

OP asked are Macrocannons effective bombardment weapons, Answer: yes.

What can we do with them?

Wipe out cities, infrastructure, bases, dams, anyhting you can 'target' and 'know' is there.

This makes sense as RT's often go out alone or in groups to raid xenos cultures, even wipe them out completely (this is not uncommon).

The idea that a macrobattery is overpowered is kinda funny...you have a mandate from the Imperium to wipe out whole species....shouldn't you have the capability?

Answer: Yes.

But do you 'have' to ?

Pop a city from orbit, call the natives, tell them to give you everyhting you want and more then say you'll be back in a year for their next tribute....profit.

Of course you need to KNOW where the population centers and military bases are. thats what sensors are for, if they work. If not you can send down soldiers to recon. Your a one stop shop being a RT....that is what you DO.

Orbital defenses getting your macrocannon shells before they get the xenos? Pull up to high orbit and lance the hell out fo the defending weaponry. Or send in strike teams to cripple them...your Arch militants are there for a reason.

Its supposed to be FUN to conquer, compel and wipe out the xeno...Have fun the Emperor is watching.

Aye, I think a fair bit of "handwavium" is needed for it to actually make sense. I mean, in the Gaunt's Ghosts books, whenever they talk about orbital bombardment of cities, it takes several hours to get close to destroying a city.

Like most bits of the 40k setting, it makes no sense using the actual laws of physics. Otherwise how could close orbital support (which also happens in the novels) work, since if they hit with that much force, the troops that are 1-2km away (as they usually are in the books) would be wiped out.

The idea that a macrobattery is overpowered is kinda funny...you have a mandate from the Imperium to wipe out whole species....shouldn't you have the capability?

Answer: Yes.

Sure, with a warship armed with big guns . Not any ship armed with any weapon.

MILLANDSON said:

Reminds me of a bit in the Posleen Wars series (not a 40k series) where a soldier, bereft of normal radio communications, looks up artillery support on the backup comms system (telephones, iirc), and calls in a strike ~300m odd from him, and gets the warning "Danger Close" (read: you may well be caught in the blast). Turns out he'd reached the Missouri , not the light mortar battery he thought he'd called...

I'll note, in defense of scary orbital bombardments, that most of the force is actually wasted crater-making (especially if there's an actual warhead, which is impact-fused), and dense kinetic strikes have a serious problem with over -penetration (and, unlike humans,planets don't go into hydraulic shock). Added to that, you can have fun with propellants and trajectories (plus old-fashioned parachutes) to adjust the impact velocity, maybe tone it down a little. For example, if our hypothetic 40kg BFR isn't fired, but merely "dropped" with negligible muzzle velocity, it'll still impact at 11.2km/s. That's "only" 557.5 tonnes worth of kinetic energy...

As for the example in Gaunt's Ghosts, if memory serves, that was a call from Corbec to Kreff, the XO of the ship they had travelled on, yes? That ship (the Navarre ) was a frigate, and if memory serves, wasn't described as having a lance, meaning (given the time that scene was written) she was probably intended to be a Sword-class. The Swords were noted for being fitted almost exclusively with laser batteries. Still going to throw up a hell of a lot of debris, plus some very impressive atmospheric overpressure (followed by implosive cavitation), but probably safer than being near a KIS impact.

To me, this couple of pages has clearly shown one thing: Whatever you say or think about this question cannot be wrong, because reasoning does not really work in 40k. ;-) BTW, the last time my players fired their macrocannon towards a planet surface, the hit left behind a crater of 50 metres in diameter.

Graspar said:

Your RT ship IS a warship with BIG GUNS.

bobh said:

Except, you know, when it isn't. Like when it is a transport armed with basic macrocannons. Macrocannons such as the thunderstrike or mars.

I've got no problem with orbital bombardement, but I think that the ability to wipe out cities with ease should be limited to more advanced weapons such as lances.

Alasseo said:

Actually, the Navarre was stated as being a Firestorm -class "grand" frigate. And it was indeed equipped with a prow mounted Lance weapon. It's how it killed another frigate in short order in Sabbat Martyr before itself was destroyed.

-=Brother Praetus=-

@Graspar

Except, you know, when it isn't. Like when it is a transport armed with basic macrocannons. Macrocannons such as the thunderstrike or mars.

I've got no problem with orbital bombardement, but I think that the ability to wipe out cities with ease should be limited to more advanced weapons such as lances

The only weapons I wouldn't credit with the ability to be viable for destroying cities at least with prolonged bombardment would be point defense turrets. Even the humble thunderstrike is an order of magnitude beyond what Titans employ, after all.

The potential energy of sitting at the top of the gravity well is just huge, forget guns, your transport barge full of mineral ore is a deadly threat planetside, dump a dense cargo out (metals) and its a serious threat, let a alone an attempt to weaponise such a thing. lets not even go into the ships themselves or their propulsion systems....

@Alesseo "For example, if our hypothetic 40kg BFR isn't fired, but merely "dropped" with negligible muzzle velocity, it'll still impact at 11.2km/s. That's "only" 557.5 tonnes worth of kinetic energy..."

Thats what I was saying before about tactical bombardment options, an 'Ortillary array' on the underside of the ship, that drops stuff like that, along with missiles and lasers with wavelengths suitable for atmospheric attacks (infra-red is good)

obviously to each their own, but I'm pretty happy with my spaceships being appallingly dangerous.

Graspar said:

I'd say a fleet armed with big guns . A single ship shouldn't have the capability to destroy entire races, which following most people's suggestions here they would.

As for the Gaunt's Ghosts comment, I was actually on about "His Last Command", where to destroy the strange hive-esque "step cities", it's stated to take several hours of bombardment for each city, and they aren't even protected by voidshields or the like.

Back when I was doing stuff in another game system, I did introduce the 'Nuke' for fun and amusement value, just dredged up my notes from all those years ago and the kiloton incremental scale had 1kt absolutely wreck a 200m radius 'completely toast', everything in a radius of 500m is probably best described as 'completely broken' and everything else in a 1500m radius was 'mostly broken'

According to 'the internet', a place like NY, which is a big a place as any, is about 790square Km.

Its going to take a while with macrocannon strikes which have 1kt yield each shot.

I've got to say I'm surprised at the amount of math and science being thrown around when the 40K universe works on the theory of "if it's cool, it works". Hell, the entirety of Ork technology only works because they BELIEVE it does, defying a number of physical laws as well as common sense half the time. These games are epic narratives, and even if the GM feels that macrocannon shells won't crack the crust of a planet like an eggshell, there's probably a good few in-cannon tricks you could pull to make it happen.

How about cutting a deal with the Adeptus Mechanicus and getting a few "Planet-Buster" shells made from that ultra-dense material they're mining in the Lathe Worlds, a scaled-up version of the Lathe Body-Blower shells.

Or maybe you'd prefer to use your political clout and actually request the assistance of a faction who actually does have access to the kind of planet-destroying equipment you seem to desire, whether it be the Mechanicus, the Inquisition, or if you've been REALLY working hard, the Adeptus Astartes themselves.

Rogue Trader is a sandbox game for a reason; it encourages out-of-the-box style thinking to approaching problems and usually rewards solutions that play to the strengths of the various players in the group. Say your ships weapon systems aren't up to snuff, or the city has ancient defences that make a "frontal assault" unwise; time for a daring infiltration mission with a small team to plant a bomb or two in key points of structual weakness or the powerplant keeping all those nasty plasma batteries powered up.

As to the question that started it all, I would say that Macro Cannons would certainly cause horrendous surface damage, but be pretty inaccurate and more of a "spray and pray" style of weapon in terms of bombardment.

A number of points

1) The masses of RT ships is wrong. This was noted way, way pack when parts of the game were reveiled as a preview. If you do the math and compare the volume to the alleged weight then you have a density about equal to air.

2) Macrocannons can be used as bombardment weapons. That's been part of 40K for a long, long time. The IoM uses a number of materials far stronger than those of modern human science (15km tall hive spires anyone? Ceramite? Adamantine?) and that can include shells.

3) The warheads on Macrocannons will be massively devastating, nuclear at the minimum. The velocities required for them to be of any use in ship combat over tens of thousands of kilomters means conventional explosives will be irrelevant compared to kinetic energy of the shell (Atomic Rockets has a cool section about this kind of stuff). Since this is 40K this doesn't rule out plasma, melta, or vortex warheads but does mean they will pack a hellish punch. Execution Hour mentions megaton level explosions being used as anti-fighter flak bursts.

4) Lances are used as precision orbital fire weapons not because they can hit a house and not blow up to the one next to it, but because they can blow up a neighborhood and not lay waste to the city. Compared to what is essentially a volley of nuclear weapons, a weapon that will merely annihilate a football stadium with some precision is fairly accurate and more useful as (comparatively close) tactical support.

Cynical Cat said:

I just checked that with the numbers of the Vagabond Trader. Assuming it is a simple cuboid and about as high as wide, you get the following volume:

2,000m long * 400m wide * 400m high = 320,000,000 cubic metres

Filled with air (density of roughly 1,2 kg per cubic metre), this cuboid would have a mass of roughly

320,000,000 cubic metres * 1,2 kg per cubic metre = 384,000,000 kg

wich equates 384,000 tonnes or 0,384 megatonnes.

The Vagabond obviously has a density about 20 times higher than the density of air. And the relations are similar for all other starships I checked.

It's also worth noting that the shells are going fast, but they're not going that fast compared to most sci-fi kinentc weapons. Given that turns are 30 minutes long, Mars-Macrocannon shells only have to go about 67,000 m/s to impact within the same turn. Outside of Rogue Trader, there are plently of BFG fluff about broadsides hitting there targets 1-2 hours after being fired.

Lances still cause exessive damage to planetary targets in the area, not from the direct blast, but from secondary damage, such as vaporising rock. Don't forget that Lances often go in one side of a ship and out the other - even ships with armor that can handle barrages of macrobattery fire. That's not just going to take out a conventional city block, but several meteres of what ever bedrock the block was sitting on. Though I'd argue you'd still have to hope you hit the right block, nothing in the 41st mellenium is as precise as we think it should be.

But ultimately, as with most of 40k, particularly Rogue Trader, ship weapons are exactly as precise and powerful as the GM needs them to be.

Terelo said:

You're right, I misrembered the calculations. It's David Weber's Honourverse vessels that were less dense than air (he corrected by keeping the mass and changing the volume) RT ships are heavier than air, but far less dense than modern military vessels.

Well...if you want to change the fluff and make a macrocannon weaker that it should be go ahead. But...you could simply disarm their ship. Plenty of unarmed transports out there.

Any 40K starship is going to be able to massive damage to an undefended planet, if need be by going out and grabbing a few asteroids and towing them back as kinetic bombardment weapons. As a general rule in sci-fi, the effectiveness of a reaction drive as a propulsion source is proportional to its effectiveness as a weapon and any drive powerful enough to get you anywhere interesting in good time is powerful enough to cause immense damage. 40K certainly falls into this category.

Any Rogue Trader has enough power to scorch a civilization without antistarship weapons, but a ruined civilization is worthless. It doesn't get the Rogue Trader anywhere and it costs resources. Even modest planetary defences like a few hardened torpedo silos or a cluster of defense lasers means there is very real risks if the Rogue Trader attempts it. This is the scale the game plays at. Rogue Traders have powers that rival that of planetary governors and that's for good reason. Players that use such power recklessly can cause a lot of damage . .. and make a lot of enemies in the process. If he wipes out villages of alien primitives to make the world a better colony site he might end up supporting his colonists in a costly guerrilla war against alien survivors that costs him time and resources while earning the emnity of the Rogue Trader who used to visit the world every five years and trade for the aliens' harvests of beautiful shimmercoral .