I am trying to draw up some scratch maps for my groups ship in Rogue Trader and was looking for some advice from the board.I know that the details of many items are left vague, but I'm sure people have had thoughts on this before and come up with some ideas.

How large would an individual gun in a macrobattery be and how many would there probably be in a single installation? I am specifically thinking about Sunsear Laser Macrobatteries in this case, but other ideas would also be appreciated.

I asume that the massive circles/holes on the side of the ship models in BFG and on many of the pictures in the various sourcebooks are meant to be macrocannons or similar, in which case a broadside seems to only contain a small number of cannon (5-10 on many models and pictures). This doesn't seem enough to me from the descriptie text in the Rogue Trader books which implies dozens of guns in a macrobattery.

Any input would be appreciated.

sizes range (in the texts) from tank to house sized shells. since most tanks are 50 to 100+ tons you can guess A shell is around 25 to 50+ tons. this assumes that the propellent and explosive weighs less than armor. not sure if a laser battery would have shells.

modern artillery batteries consist of 6 to 9 guns or missile launchers.

The fluff implies that a macrobattery has many individual weapons "rank upon rank", but the exact number isn't specified anywhere I've seen. The individual weapons are often described as house sized to hab-block sized.

That said, I do have a couple of comments:

One, when they're speaking of the projectile, don't assume the 'tonnes' is the actual mass of the shell. It is traditional to refer to warheads by the yield - the equivalent weight of TNT when the fuze lights off. For example, the real life Hiroshima bomb was about 15 kilotons yield. The actual mass of the device was 9700 pounds. So, when a macrobattery fires a "one kiloton shell", that may mean the force of the impact, plus the warhead, is equal to a thousand tonnes of high explosive. 40K warheads presumably use something nastier than chemical explosives (plasma, melta, or nucleonic warheads are all possibilities) so the shell doesn't have to be humongous to hit that hard. We do have an official size for torpedoes: sixty meters long. Since torpedoes need to track ammunition, unlike macrobatteries, and are described as much larger in the fluff, that sets an upper bound for the size of a macrocannon shell. Shells still probably require a gang of ratings with chains and pulleys to load.

Two, I have seen several fanfiction authors who assumed the number of guns was strength x 10. So a Lunar cruiser, with a strength 6 macrobattery in its broadside, would have a "sixty gun" broadside. (Plus the two lances in the other weapon component.) This is, to my knowledge, completely unofficial, but I've seen enough people use it to consider it a decent guideline.

Cheers,

- V.

Thanks Vandegraffe.

I have always interpreted the kiloton, etc. references in a similar way (yield not mass).

I like the Strength x 10 idea as a starting point for number of guns - the more guns, the better chance of getting numerous hits. I'm not sure If I can fit all of those weapons onto my plan, but we will see.

I am trying to roughly map out the location of the gun decks etc. at the moment (for a Sword-class frigate). Swords have two weapon slots, both dorsal-mounts. To me this implies some form of gun deck with turrets, akin to an old battleship (though far, far, more numerous). This would allow the weapons to cover the forward, port and starboard fire arcs as described. I am picturing some kind of tiered arrangement so there are several "steps" of guns along the forward decks of the ship.

You may find this helpful; http://the-first-magelord.deviantart.com/gallery/8686311#/d1cy8l1

The Strength x 10 model may actually fall down, depending on the Component fitted- we have a canonical lower limit for the number of macrocannons firing in a broadside arc on a "stock" Lunar class: there's a section in Cross The Stars trying to guesstimate the crew size. As part of that, (the starting point, in fact, as the character doing this was pressed gun crew) they start by taking the number of crew to service one gun (and, iirc, gives the dimensions of the gun bay), one gun per bay, 40 bays per deck on this side of the ship. There's no mention of how many gun decks there are, but it gives us a nice figure to base calculations on (ie- for every extra gundeck we figure is part of the component, we can add another 40).
Assuming that such a Lunar carries a pair of Lance batteries in her after broadside slots, and Mars pattern Broadsides in her for'ard, we can then play around with the number of decks until the number of guns becomes an easy multiple of 6 (or whatever the component's Strength is, don't have the book handy) and use that for macrocannons of comparative firepower.

Specifically for a Sunsear- well, I haven't worked up a numbers estimate for them, but as far as size goes, possibly work on this as a base for comparison?

I think the model is a little small. the inside cover illustration of the imperial guard codex has some planetary defence cannons that look like hive spires! But is suspect that they would be more like lances. I guess the rough answer is How many do you want? Some macrobatteries may fire machine gun like bursts of MOAB size ordnance, while others fire single shells of colossal size in cannon esque volleys. I've always thought of sunsears as being like turbolasers from starwars, several ranks of them (perhaps 12* strength), whereas plasma batteries were far more like artillery pieces. simple mars pattern batteries were like the main guns of first world war dreadnoughts, with multiple guns sharing a turret and unleashing broadside fire in order to blanket the enemy with shells

either way, each weapon probably has is own turret, the size of a large apartment block, with heavily guarded hoists lifting shells from deep within the ship (or fuses, primers etc). these will be one of the busiest and most heavily regulated parts of a ship, because of their strategic and the danger posed to the rest of the ship if the enemy or carelessness causes the ordnance to go off inside the battery!

The free sample adventure for Black Crusade features an Imperial prison barge (so a Transport sized ship). Page 19 and 20 gives a brief overview of the Gun Decks but even on a transport ship it describes thus…

'Even though the Chains was lightly armed for a vessel of its size, it still carried twin banks of macro cannon down the length of its hull, massive guns easily capable of reducing ground targets to dust with prolonged bombardment.'

From this we can take it to mean that it is a Transport sized vessel with a pair of Macrocannon in a dorsal mount. It then goes on to describe the ships magazine being in the prow of the ship (certainly a central theme in militarized vessels of the Imperium where some have torpedos or nova cannon requiring ammunition in a forward, central location) with loading lifts over 100 metres high. Finally it describes the Ordnance Gallery as being central to the gun decks, from where the master armsmen and chief gun marshals could direct the gun crews in loading and firing the macrocannons.

The ship is described as being thousands of metres long and hundreds wide, and the macrocannon batteries run its length (certainly not ALL of it) so lets say they are 1000 metres long. This sounds about right if you consider that the Ordnance Gallery would have a field of view of approx 400 metres for fore and aft, easily manageable with image enhancing pict screens or binocs and a vox system to blare out commands to the crews.

Next up, consider the space that weapon systems take up. Whilst advanced weapons like plasma, melta and laser batteries (because of the energy systems invovled), lances (due to focusing apparatus) and torpedos (long tubes!) all take up vast internal space… most basic macrocannon systems only take up a couple of space points on a vessel. I take this to mean that whilst they may run the entire length of the vessel they are actually quite compact. As the ordnance they fire is stored in the ships magazine (a component that FFG have entirely glossed over) i can only assume that the space listed for a weapon does NOT factor in ammunition storage, merely the size of the weapon itself. So the guns themselves may be snub nosed, or deploy out of the hull in preparation to fire or any other manner of ways to save space. Space for thousands of crew to service and operate them. All in all they couldn't be more than 150m long, or else they would be back to back across the hull without any space for an internal superstructure. So if the vessel is 400m wide, 150m per gun is 300m width of gun, leaving 100m of internal structure, bulkheads etc.

So in conclusion, the linked piece of deviantart art looks pretty accurate if you ask me!