I'm currently working on an NPC ship that's essentially a large transport converted into a massive weapons platform (as in a platform to carry a single massive weapon). The cargo holds are going to be replaced with reactors and such, but I'm having trouble deciding on the stats of the weapon itself.

I was considering one of the Lance-Batteries usually reserved for battle cruisers, but that seems lazy/underwhelming. It's going to be vulnerable as all hell, which is fine, but I feel like it should have some sort of weaponry that reflects its specialized-beyond-any-feasible-use-beyond-one-very-specific-thing nature.

I can appreciate your gusto, but I don' think you could mount a capital class weapon on a small ship under any circumstances. Those things are multiple stories high. You would probably be good to go mounting a volcano cannon onto it. Those things are terrifying close air support weapons. They are normally only mounted on titan variants. What kind of damage do you want it to do? Do you want to wipe out a man / a tank / a building / a block / or a city? Volcano cannon for the record would annihilate a building

EDIT: I just realized you meant a voidship transport...not a cargo transport for getting material to the surface

Ah, yes, I can see why that would be confusing. Although now I kind of want to mount a lance on an arvus lighter...

I had suggested converting a Transport to mount nothing but a Nova Cannon to my GM once. The ship was essentially rebuilt around the thing.

I had suggested converting a Transport to mount nothing but a Nova Cannon to my GM once. The ship was essentially rebuilt around the thing.

That's pretty cool, but I'm looking for an energy based weapon. The lance is going to be channeled through a massive Chaos shrine/focusser thing, but I don't see that working as well with a projectile.

You can mount something like dragonbreath lance, or whatever its called. From Lure of The Expanse, str 3 lance, that hits every 2 DoS, but has very limited range.

Take a look at the "Jury-rigged" and "structural impact" penalties from having a cargo hold strike craft landing bay (it's in Battlefleet Koronus I think) - you might want to include this to the ship's stats.

I would then use a Godsbane or Voidsunder lance battery there, depending on the range you'd like to have.

However, I don't see why even dark mechanicus would put such valuable weapons on a transport.

Maybe you should take a look at "Da Wurldbreaka"s guns for inspiration.

You could instead, amass 3 broadsides of Mars/Thunderstrike Macro-cannons (more common & "disposable"), aimed on the front side of the ship or something like it.

Or maybe a huge choir of chaos psyker, prepared to set an enemy ship ablaze in fire and demons invocations or... on shooting a "warp lance" like the one the Whisperer use in the endeavor that comes with the GM's book.

Alternatively, since we're talking about a Chaos shrine powered weapon-thing, just use the stats and rules of a Nova Cannon, or even torpedo tubes (fluffy words on that to follow in a bit), but assume that it's actually an energy weapon powered by rituals and sacrifice and screaming people. Or assume that they are daemon weapons, and therefore have no need of ammunition.

I find the image of a shrine propelling a rift forward that rips a great hole into the warp compelling, which sounds like the archeotech vortex Nova Cannon. I also find the idea of a shrine generating a field that spits out semi-directed bolts of warpy doom interesting- those could be modeled after Torpedoes, vortex or otherwise.

This is a thoroughly blasphemous conversation...I am bowing out now!

For some reason I really like the idea of the torpedos. It feels like the ships from gaunts ghosts.

Of course, a Nova Cannon would be pretty dramatic...

Also, anyone have any rules for ships protected by warp magic? I was just going to give it an extra void shield.

Depends on the nature of the cult. Tzeentch? Void shield(s). Slaanesh? Defense modeled after the Dark/Eldar void shield replacements (cannot recall proper names. Ghost field? Shadow field?). Nurgle? Regenerate hull points, possibly quickly.

Slaanesh? Defense modeled after the Dark/Eldar void shield replacements (cannot recall proper names. Ghost field? Shadow field?).

Eldar use ghostfields, DEldar use Shadowfields. Both are explicitly incompatible with normal shields.

Personally I'd instead give them a few psykers, able to use Delude and the like as per Into the Storm and Navis Primer.

Focus on Telepathy tricks rather than the "setting stuff on fire" telekinetics. And note that I'd put more than one psyker aboard each, meaning that fatigue isn't quite as much of a joykill.

I had suggested converting a Transport to mount nothing but a Nova Cannon to my GM once. The ship was essentially rebuilt around the thing.

Fire the Wave motion gun!