One of my players wants to bind a daemon to a new torpedo tube the group recently salvaged and then install it on their ship. Fluff wise, this seems reasonable so I'm hesitant to disallow it regardless of obvious potential "balance" issues. That said, I don't think it should be easy or risk free. Basically I'm thinking about using the rules for daemon weapon creation and just modifying the effects as appropriate to adapt to the different scale of weaponry. A crew member will be designated as the wielder/operator of the component and will have to make the relevant daemon mastery tests and suffer the consequences of failure.

I'm looking for suggestions on how to make this work rule-wise and fluff-wise. I'm not so concerned about arbitrary balance but I would like to up the consequences and difficulty a bit. Any ideas?

Wouldn't there be an unbound demon unleashed on the ship the first time this component took a critical hit?

Personally I'd be tempted to say that it's possible for something like lances but for something where the component is essentially a tube and the torpedo is doing 90% of the work then the bonus would be almost negligible and the risk would be quite high.

Different if perhaps you were running a Black Crusade game and you could 'work with' the demon rather than binding it to the tubes... though the deal still wouldn't be great for the players.

Actually the threat of a daemon getting loose sounds like a good possible balancing factor. Of course it could largely be offset by a tenebrous maze. I figure daemon bolters are fine and that is a similar case of fancy ammunition being replicated - just at a different scale. I think the player's main reasons for wanting to attempt this are:

a) b/c it is good old fashioned radical fun

b) it trades the supply issue for torpedo tubes into risk management for the souls of their crew and heresy. This group is big on minimizing supply issues. (for example, only using laser based macro-batteries so they don't have to worry about getting shells)

I would say that seeing as torpedo tubes have to be built into wired into the ships systems so that they can be fired by the big red button on the bridge that a tenebro maze would not make any difference to the demon. He/She is literally bound to part of the ship. Should that binding fail due to heavy ordinance or some other mishap I'd assume the demon would just flow into other parts of the ship and possess different components or just slaughter crew for a while before fading into the walls.

Actually depending on the demon it might just possess the nearest ratling and hide out until it can do something devastating.

I always though demon bolters (Kai guns?) were more of a focal point for the weilder's emotions/powers, even then it only produces small blasts despite the power level.

A 40k torpedo is unimaginably massive

Torpedoes are large anti-starship missiles used in space naval battles. They are a highly versatile weapon, as they can be used by any spacecraft from the largest battleships to the smallest planetside missile defence silos. Up to 200 feet long and powered by a powerful plasma reactor that also forms part of the warhead.

In my mind a demon that can manifest salvos of torpedoes at will is going to be pretty powerful, far too powerful to really want to have onboard your ship. Imagine the stress it will put on the gellar field.

Others may feel differently but I'd probably only let players succeed in binding a demon that could hurl torpedoes out of the tubes with the force of it's hated alone rather than one that could actually manifest warp based analogues. Even then the reduced power requirements for the tubes would be offset by the increased power requirements to keep the demon bound.

Hmmmm actually Stars of Inequity has something that might fit in this situation:

That is actually a lot nicer than I'd be in the situation but still that is how the rules recommend doing it. Still with the rules as written you'd still need to supply the torpedoes. If you want a quick ruling I'd remove the damage bonus and reduce the power reduction to be just a single point (minimum zero) and then remove the need for ammunition. I'd probably also (at least) double the penalty if it gets affected by a critical hit as a demon that can manifest torpedo salvos should be a being to be feared indeed.

Modifying stars of inequity isn't a bad idea. I'll probably go less abstract though. I could see either loosing the demon (which the PC's would then have to go fight) or possessing the operator of the weapon. I envisioned a poor sap strapped to a chair that is part of the possessed weapon who controls it based on orders he's receiving from the bridge. Ala psykers in the Imperial guard, he'd be closely supervised and put down rapidly if he showed signs of loosing control. This would minimize the integration issues you mentioned before. I'm envisioning sort of a hybrid daemon engine/weapon.

Regarding the power needed to produce torpedoes: I always thought of daemonic weapons pulling off some sort of temporal warp cloning shenanigans to create temporary copies of the ammunition that was in the weapon when they were bound. I doubt there's cannon fluff one way or another on this but it is what makes the most sense to me.

Given this is 40K and grimdark as it can be I'd probably rule that if you want to slave the weapon system to a demonhost then one regular person cannot contain a powerful enough demon to do what you want. A high level psyker could but you probably want the high level psyker doing more than firing torpedoes in space combat.

For that you need a squad of demonhosts in a choir like arrangement like a grotesque parody of an astropathic choir. That way you could have your astropath or some other psychic PC overseeing the choir and make all the testing that players responsibility.

If one of their 'choirboys' starts behaving oddly then the player can either execute him safely (a procedure which requires the ship to raise the gellar fields and turn off all void shields), execute him quickly (chance of an unbound demon being released... not at full health because of the execution but still) or monitor the situation.

Every choirboy missing decreases the strength of the torpedo salvo you can fire so while you don't need to reload torpedoes you probably still need to have someone create more demonhosts from time to time.

The component would take no power and give the ship a -5 penalty to morale as it is so very heretical and exudes an aura of palpable malice.

A critical hit to the component kills 1d5 choirboys in addition to the standard critical effects.

Yea, as a GM liking to simplify things, I'd say it still has to use torpedoes but it gets a bonus to hit (+5 or 10). Like another component in BFK.

I appreciate the suggestions so far. The Choirboy idea in particular is fun and flavorful. I was thinking of going in a different direction though. Here's a rough outline of what I had in mind. Feedback is appreciated!

Daemon Weapon Creation for Ships

Must first learn the true name of a greater daemon (forbidden lore)

must then alter an existing component to be a suitable vessel (forbidden lore, tech-use)

Must prepare the ship for installation (forbidden lore, tech-use)

Must bind greater daemon to the weapon (forbidden lore, daemonic mastery) - take into consideration special conditions for type

If failure, then possession, uncontrolled greater daemon, etc

If Successful, determine ability based on weapon type and daemon type

Also, adjust power requirements to 2 (to maintain techno-arcane wards) increase space by 1 for lances and macrobatteries, 2 for torpedo tubes, broadsides, and lance batteries, and 4 for nova cannons to account for the room these additional wards require.

macrobattery must repeat the binding once per str, no ammunition required after binding

lance none (for battery repeat binding one additional time)

torpedo tube must be loaded initially with chosen ammo, increase difficulty by +10, no ammunition required after binding

nova cannon increase difficulty by +20, no ammunition required after binding

(for landing bay, treat each fighter/bomber as a daemon engine per black crusade rules)

BENEFIT

Khorne: Increase damage by 2 OR decrease crit rating by 1

Nurgle: if this weapon suffers a critical hit, roll d10. On a roll of 4 or greater ignore the critical hit. OR each hit that pierces armor causes 1d5 crew damage

Slaanesh: +15 to BS skill, for torpedoes, instead increase speed by 4.

Tzeentch: each degree of success on the attack ignores one shield or 4 points of armour. OR each critical hit has a 50% chance of also starting a fire

DRAWBACKS

Permanently decrease Morale by 10

If the component is ever destroyed the bound daemon appears and wreaks havoc upon the ship

Daemon mastery test required to fire weapon - risk of possession by firing character.

I'm gonna be honest, this seems childish in the extreme. If your players want to start binding Greater Daemons of Chaos , beings so powerful that entire groups of the Ordo Malleus study them individually for centuries and can sway planetary populaces to their side given enough time, into their ship for ammunition purposes?!

That's just laughable, honestly. If you want to go with a Daemon Vessel, wherein the entire ship is inhabited by scores of lesser daemons that pervade every bit of it, then go ahead and play Black Crusade.

Well, that was constructive. This is 40k after all so I expect things to be a bit ridiculous at times. Personally, it doesn't seem out of scope of the game as multiple books in the 40k rpg line give rules for binding greater daemons into personal weapons such as swords all the way up to full on daemon engines. I fail to see how this is any more "childish" then the rest of the setting. Perhaps the bonuses and drawbacks both need to be made more extreme, but I don't see a problem with the basic concept - something occupying the space in between a daemon weapon, ship, and engine.

In my mind the scope is the problem. I'm not aware of any rules that allow for the binding of greater daemons but binding of daemons in general is possible in 40k.

The issue is that it generally isn't done on a large scale and when it is it is done by the forces of Chaos rather than the forces of the Imperium. Radical inquisitors do use daemonhosts and daemon weapons but they don't (as far as I'm aware) create daemon engines as this seems to require high level pacts with chaos entities that even the most radical inquisitor is reluctant to enter into.

That said if that is a direction you want to head then I'd say it shouldn't be something the players can just achieve with a few dice rolls. It should be much more involved and potentially the focus of the arc of a campaign. Rogue Trader uses Endeavours for such things.

The best way to think of an Endeavour is as a business venture by the Explorers—an investment of time, resources, and sometimes direct influence all intended to turn a profit.

Rather than turning a profit the Explorers are looking to completely remove their ammunition requirements. Okay fine. The steps you outlined above make sense so lets adapt them into the Endeavour system.

Grand Endeavour: Create and install Daemonic Torpedo Tubes

Objective 1 (Criminal/Heretical) (800 points)
Uncover the true name of a suitable daemon

Objective 2 (Creed, Criminal) (400 points)
Sanctify a vessel and all components that will be used.

Objective 3 (Creed, Criminal) (800 points)
Summon the daemon and bind it into the vessel before it butchers you all.

The benefit would be the torpedo tubes with unlimited ammunition and a small bonus depending on the type of daemon bound.

Khorne - Blood for the Blood God = Each successful (damaging) hit gives the component +1 damage for the remainder of the combat.

Nurgle - Pestilence = Each successful (damaging) hit does +1d5 crew damage to the target vessel

Slaanesh - Seduction = Each successful (damaging) hit does +1d5 morale damage to the target vessel

Tzeentch - Changer of the ways = Opponents must reroll successful attempts to shoot down ordinance

The drawback would be

Morale reduced by 10

Destruction of the component releases the daemon

Penalty of 20 to all warp navigation rolls

Plus a penalty based on the type of daemon bound.

Khorne - Blood for the Blood God = Operator must make a challenging willpower test to not fore the weapon at every given opportunity. Each successful (damaging) hit in a combat gives the daemon a chance to escape.

Nurgle - Pestilence = Infection spreads readily through the crew. The Triage extended action is now impossible and decrease morale by a further five points

Slaanesh - Euphoria = Decrease crew skill by 10 increase morale by 20

Tzeentch - Changer of the ways = Fate points burnt or spent are only successful 50% of the time

Those refinements get this idea pretty darn close to what I had in mind. I could see giving a few random options for each daemon type (chaos afterall, and precedent from daemon weapon rules) but this seems reasonable and thematic. As far as being out of scope, I'm certain that Dark Heresy specifically covers binding greater daemons in its rules for Daemon weapon creation. They are treated just the same as lesser daemons albeit with a significantly higher willpower. Thanks for the constructive input - my little radicals are going to have a blast. If I end up expanding this idea further I'll post the updates here.