So, I'm using the Tau as a primary foe for a chunk of a Rogue Trader story (might get adapted to a game, at a later date), and I have a question set, regarding them:

1. If I dig a bit, one of the first game ideas GW did was something along the lines of Space Hulk, if not that, where Astartes would board a derelict ship, and try to kill Genestealers, or servants of Chaos, and I hardly see why the Deathwatch, here, couldn't be called upon to do the same, or maybe some of the Astartes seconded to the Crusade (Ebongrave would probably love to see Space Marines assault their way through Tau ships ). Any ideas on Tau-specific obstacles, and more, a boarding party, be they Deathwatch, or mere mortals, might encounter, if needing to rush a Tau ship?
2. Air Caste - so, we all know that, in the bulk of stuff, the Fire Caste are the only Tau who seem to get screen/fluff time, in GW products, as this is a war game, and they are the military part of the Tau (with the Ethereals sneaking in, granting some support/buffs), while three other Castes are sort of marginalized into about as many sentences in the fluff, but we know that the Air Caste would be aboard ships, and that they are accustomed to low-G environs. How might they be in water, though? Do you think they'd find the ease of movement to their liking, or would the resistance of the water quickly overcome them?
3. We know that higher-ranking Fire Caste get to wear suits. Do they make any for any other castes, maybe more for tasks, and less for combat, or would drones always be a better option. If the Air Tau were good in water, I'd wonder if they might get light suits to assist in mobility, and protect them from the pressure, at lower depths, or if they'd just make their drones amphibious, and not expect actual Tau to have to do so much? In space, would the Fire Caste, alone, be called upon to repel boarders? Would the Air Caste assist, and just get shot up? Would even the Fire Caste, up there, be using Crisis Suits, to repel Marines?
4. What water does to weapons - if we've ever watched Mythbusters, we know what water does to weapons fire. Depending on whom you listen to, even a world-changing cataclysm, like a meteorite, can have significantly different impact (pun not intended) based on what it lands on. If the Tau, or someone else, built an Atlantis-analogue city (seems they could, at least), and you had to assault it, what's your best bet? Drop pods don't seem too likely, while "amphibious" isn't usually something I think the Imperium has to fight against, and I'm not even sure how much orbital bombardment will be effective, if you have a few thousand feet of water between the target, and the spot the bombardment will land (sort of like hiding your base deep within a mountain). If the enemy fled their orbital installations, and made for the deep blue, where their planet side fortifications are, how would you follow them?

Thanks much, and have a good one. Not sure if the Jericho Reach really has any balls of water in it, officially, but I can always hope this helps someone else's game along, too. For me, a force needs to, eventually, out some Tau from a waterworld, if they ever hope to be rid of them, and I'm trying to get an idea for the various problems they can run into. If you've poked over to the RT forum, I've babbled a bunch over there, too; figured there is at least as much Tau knowledge over here, where they actually "officially" feature into the material, so I'd ask around. Have a good one!!!

Think hi tech.

Tau ships might have internal force fields meant to isolate breached areas to minimize airloss.They might block intruders too. In addition to fixed force field bulkheads tau might have mobile shield drones meant to seal off air loss in any location. These too could block intruders.

Gravity plates. What if the tau can control gravity in sections of the ship? Suppose they can rapidly fluctuate gravity levels in parts of a ship? imagine trying to walk, run or fight when gravity could be flucuating wildly. Rapid gravity shifts may throw off bolter shots as the bolts are affected.

Security drones. Obvious.

Flashing the lighting rapidly. Ship security forces might have their helmets linked to the security system so their visual systems auto compensate for rapidly shifting lighting. Intruders suffer penalties on vision.

A tau ship with an ethereal on board will most certainly carry a guard squad willing to die for him, as will the ship's crew be.

Engineers. Tau earthcaste may not be trained fighters but ship board engineers and repair teams may well carry emergency tools capable of doing great harm if used an improvised weapons. And they will know the ship very well. Ambushes, use of air vents as spider holes, possibly even spare Hull plates welded over important doors are possible. Also even a glancing touch from a fusion welder may breach a marine's armor.

Hull patch foam. Tau drones may be equipped with emergency sprayers that deploy a thick, sticky foam that adheres and hardens to seal Hull breaches . imagine what effect a spray of this might have on a marines armor, vision, weapons, etc.

Actually finding their way around the ship! Tau astetic being what they are: smoot walls with doors that aren't quite hidden but they don't stand out either. Markings (level, room number , direction) is all in Tau and also quite subtle. And while in Imperial craft you can find the engine room by following the noise, that's a lot more difficult with the Tau reactors who put out way les noise. Check out the Last chancer's novel " Kill Team" for a great description of what the inside of a Tau spaceship looks like.

Sadly no water in the novel: it describes the atmosphere on board as warm (towards hot) and dry.

Now for some threats I think you could encounter:

Drones.

More drones.

Even more drones. No seriously, expect entire racks of combat drones deploying to repel boarders.

Tau in the new codex also have Pulse blasters the Tau equivalent of a shotgun.(A shotgun that shoots plasma rounds. Up close, if you are not in terminator armor, you're in trouble.) Expect Fire cast troops onboard the ship to be armed with them.

Tau stealth teams. The ship's fire warriors might not have those, but they will make a great surprise for your players.

Maybe some AI controlled centry guns in the walls and ceiling (altough I'd personally use racks of combat drones instead.)

Forcefields to close of sections of the ship.

Probably NO battlesuits, since Tau aren't imperium-level stupid of shooting overkill anti tank weapons down their ship's corridors.

Maybe an ethereal on the bridge? Remember if you kill one all the (nearby) Tau go berserk!

That's my ideas for now If anything else pops up I'll let you know.

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Tau in the new codex also have Pulse blasters the Tau equivalent of a shotgun.(A shotgun that shoots plasma rounds. Up close, if you are not in terminator armor, you're in trouble.) Expect Fire cast troops onboard the ship to be armed with them.

That's my ideas for now If anything else pops up I'll let you know.

don't forget alien allies. While kroot may not be great ship action forces the tau hhave other allied species.

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Tau in the new codex also have Pulse blasters the Tau equivalent of a shotgun.(A shotgun that shoots plasma rounds. Up close, if you are not in terminator armor, you're in trouble.) Expect Fire cast troops onboard the ship to be armed with them.

That's my ideas for now If anything else pops up I'll let you know.

Are these pulse blasters statted in DW yet?

They are from the latest codex (wich came out last year I think?) So I don't think so.

Here's the TT rules in case you want to homebrew them.

don't forget alien allies. While kroot may not be great ship action forces the tau hhave other allied species.

Good idea, I kinda did.

Now Kroot usualy travel on their own ships, but there's no reason why you couldn't have a group on board. Same for Vespid or Human allies.

And you could throw in other races to. Probably not the real creepy evil pro- chaos ones, but then again they once did have a very short lived alliance with some dark eldar in the fluff.

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Tau in the new codex also have Pulse blasters the Tau equivalent of a shotgun.(A shotgun that shoots plasma rounds. Up close, if you are not in terminator armor, you're in trouble.) Expect Fire cast troops onboard the ship to be armed with them.

That's my ideas for now If anything else pops up I'll let you know.

Are these pulse blasters statted in DW yet?

They are from the latest codex (wich came out last year I think?) So I don't think so.

Here's the TT rules in case you want to homebrew them.

What's TT mean?

don't forget alien allies. While kroot may not be great ship action forces the tau hhave other allied species.

Good idea, I kinda did.

Now Kroot usualy travel on their own ships, but there's no reason why you couldn't have a group on board. Same for Vespid or Human allies.

And you could throw in other races to. Probably not the real creepy evil pro- chaos ones, but then again they once did have a very short lived alliance with some dark eldar in the fluff.

Kroot may be on board sometimes, like if a shaper is having a conference with an ethereal. Not sure how effective they'd be in a ship action. I suppose some may be trained to use a vacc suit.

Vespid would lose their huge advantage in a spaceship, flight. Also the way they can go spastic if the strain leader goes bye bye may not be acceptable on board a tau spaceship. But in close quarters their neutron blasters tend to stop marines PDQ, so they would be something to consider.

If anyone is interesed I think you can accurately model a tau pulse blaster by taking the stats for a pulse carbine, reduce range to 30m, reduce ammo to 12, remove the gyro stabilized and devastating rules, then add the scatter rule. At point blank range the pulse blaster gains the tearing quality. The weapon has no extreme range, the smaller, higher energy pulse rounds it fires burn out at long range. The lower clip size accounts for the larger round needed to deliver multiple hits. The excessive recoil and scatter effect makes gyro stabilization impractical, the range it's meant to be used at make it unnecessary.

So yeah, equip your ship security with that monster!

TT means "Table Top", from the Warhammer 40,000 minis wargame. My guess is these new Tau things either appeared in Warzone Damocles: Mont'ka, or Kauyon, since the tau have been getting some decent book/codex attention, lately. Haven't had a chance to see either, yet, as I don't get to play 40k, anymore, and some of their books already cost way too much, for not playing them; I already do that with the FFG lines

Yeah, I was considering a lot of drones, and probably Stealth Suits, with weapons that wouldn't puncture walls/the hull. Other sources often hint that Tau aren't into boarding actions much, and not so great at repelling them, but these were some of the ideas, anyway.

The Tau brought some Kroot with them, but I'm not sure how many, and to what degree. The RT setting has a little "problem" there, if you will; the Kroot have real warp drives, and, while I won't do them the disservice of outright claiming they are slaves to the Tau, they haven't shared the knowledge of their worldsphere's drive with their "friends", keeping the Tau out of the warp-drive arms race. Even if one says "the Tau probably wouldn't have the means to operate it, such as no psykers", however the Kroot do this, it still stands that the Kroot could do this, for their allies, but they don't. For whatever reason, the Kroot don't want the Tau to know, and in the Koronus Expanse, where there are Kroot, about as far away from the Tau as you can be, and Spheres, I haven't decided how involved they will be with the Tau invasion, on account of the trouble it could be, to both races.

Most of the other auxiliaries, I'm thinking they would be few, and far between, on the tau flagship. Even if the Tau are more proactive, and less racist, than some would believe them to be, their best, most powerful ships, in this case, the spear of Truth is a Custodian-class battleship, should probably be an example of how the Tau can handle such, all on their own. Depending on how the story unfurls, I might even have unexpected Eldar support (how the Tau got there, and all), as Farseer Ashe desperately tries to shore up her plan, with what little personal resources she'd have (left), but I'd imagine most of the forces on a Tau flagship are Tau, or drones, maybe just a few Kroot (many of them are on the planet, or would've been dealt with earlier, in other planet side events, prior to the big showdown).

Thanks very much, folks, it's a great help. I'll see how much of this all I can finagle into my story, once the "final battle" with Admiral Death From Above begins (all Tau names mean something, right? part of why I like using them.)

Codex Tau Empire actually.

And yeah, sadly them codexes cost an arm and a leg. Or you could become corrupted and turn to Torrent, the chaos god of piracy

Interesting point about the Kroot not charing. Actually they don't share much at all do they? The vespid are rockin' the Tau weapons and special helmet thingy, but the Kroot stick with their krootrifles. I think they just sided with the tau because tau don't constantly go" alien scum!" under their breath like the imperials.

Come to think of it, not sure the tau would comprehend worldsphere tech, since the kroot suposedly got it from eating Ork mekaniaks. And we all know Ork tech doesn't work (well) for non orks.

Good point. Maybe the kroot offered their warp drive to thetau but the tau ccouldn't use it. likewise they could not maintain it or maybe even build it due to 'orky know wots' which the kroot had but the tau didn't. the kroot are an extremely pragmatic race and see the tau as beneficial so they ally with them but do not blindly submit to them.

Also don't the tau already have a 'shallow' warp drive that just skims the surface of the warp but they can't navigate deeper into it for higher speed? Maybe they already have warp drive but aren't able to go deep in it due to no psykers/navigators.

But hell, the tau do just fine for now with their limited FTL drive, and so what if the kroot go ffaster and ffurther for now? the kroot, being pragmatic, probably make a healthy profit doing recon and scout work for their tau allies.

Codex Tau Empire actually. ;

Interesting point about the Kroot not charing. Actually they don't share much at all do they? The vespid are rockin' the Tau weapons and special helmet thingy, but the Kroot stick with their krootrifles. I think they just sided with the tau because tau don't constantly go" alien scum!" under their breath like the imperials.

I seem to recall from when I was into gw, before iIccouldno llonger stand their bbusiness practices, that the kroot choose to retain their long rifle design for it's melee use but use ammunition from the tau that packs more punch than their ammo ddoes.

I may also recall the tau effectively saved the kroot from a massive ork waaaaagh sohortly after their expansion into space which might make the kroot see the advantages of tau alliance.

Good point. Maybe the kroot offered their warp drive to thetau but the tau ccouldn't use it. likewise they could not maintain it or maybe even build it due to 'orky know wots' which the kroot had but the tau didn't. the kroot are an extremely pragmatic race and see the tau as beneficial so they ally with them but do not blindly submit to them.

Also don't the tau already have a 'shallow' warp drive that just skims the surface of the warp but they can't navigate deeper into it for higher speed? Maybe they already have warp drive but aren't able to go deep in it due to no psykers/navigators.

But hell, the tau do just fine for now with their limited FTL drive, and so what if the kroot go ffaster and ffurther for now? the kroot, being pragmatic, probably make a healthy profit doing recon and scout work for their tau allies.

The Tau DO have their dipper drives, if you will, and one can easily see the advantages of them: they are MUCH safer, they are more reliable, somehow slightly less arcane, don't require dedicated specialists to operate, and on. Their only real drawbacks are that they eat power like a Sega Game Gear, back in the 90's, which is why the bigger ships have carry hooks for the smaller ones (here's hoping a few people get my "up there, but not quite OLD" reference; things ate six AA batteries in no time, and rechargable batteries didn't recharge as quickly as the next set would be depleted. Oh, our youth! ), and that they are SLOW, about 1/5 the speed of Imperial drives, if I remember right, but then the Tau Empire is small, so one might argue they really don't have anywhere so distant they need to go. If Farsight is too be believed, the Ethereals, at least some of them, know of Chaos, and might even be in league with it, whether willingly, or obliviously, so they might have an idea of what "real" warp travel could do to them, and the skip-rock drives really are a lot safer, to boot; I think they are even immune to warp storms, if the fluff I was reading is accurate. Until recently, they had no idea how big the galaxy really is; they're only now finding out how mindbogglingly big the Imperium really is, so maybe they DID actually decide, for where they need to get, and how safe it is, by comparison, to just stick with the drive they have. Might help me to not have any tension between them, and the Kroot, in the Expanse; never actually considered it this way, till now.

It really irritates me that GW hasn't detailed any of the (supposedly numerous) Tau ally xenos other than Kroot and Vespids. But that doesn't mean that you can't- a Tau-centric campaign would really benefit from some new Tau allies to throw your players off balance. If you don't feel up to designing your own xenos from scratch, there is always the time-honoured practice of 're-skinning'- i.e. using the stats of an existing adversary and changing the cosmetic description. Hence you could have Crov'leks, hulking brutes covered in red hair with a single curved horn protruding from their foreheads, recruited from a feral deathworld, who are in fact statistically just Orks (but your players don't need to know that)...

Good point. Maybe the kroot offered their warp drive to thetau but the tau ccouldn't use it. likewise they could not maintain it or maybe even build it due to 'orky know wots' which the kroot had but the tau didn't. the kroot are an extremely pragmatic race and see the tau as beneficial so they ally with them but do not blindly submit to them.

Also don't the tau already have a 'shallow' warp drive that just skims the surface of the warp but they can't navigate deeper into it for higher speed? Maybe they already have warp drive but aren't able to go deep in it due to no psykers/navigators.

But hell, the tau do just fine for now with their limited FTL drive, and so what if the kroot go ffaster and ffurther for now? the kroot, being pragmatic, probably make a healthy profit doing recon and scout work for their tau allies.

I think so, they are "working on it" (they were in the Kill Team novel)probably wont be long before they can reverse engineer one from imperial ships. Now navigating trough the warp might be the dificult part. You know with their lack of psykers...

Might also be a case of "depending upon the author" Once upon a time the tyranid hive fleets didn't travel trough the warp. And the GW retconned in the "Narwhal" biovessel who made that possible.

It really irritates me that GW hasn't detailed any of the (supposedly numerous) Tau ally xenos other than Kroot and Vespids. But that doesn't mean that you can't- a Tau-centric campaign would really benefit from some new Tau allies to throw your players off balance. If you don't feel up to designing your own xenos from scratch, there is always the time-honoured practice of 're-skinning'- i.e. using the stats of an existing adversary and changing the cosmetic description. Hence you could have Crov'leks, hulking brutes covered in red hair with a single curved horn protruding from their foreheads, recruited from a feral deathworld, who are in fact statistically just Orks (but your players don't need to know that)...

Tau + Squat Alliance!

Yeah, tau allies..... I hate to open myself up to 'captain obvious' remarks but what about some of these xenos races the imperium have been exterminating? Maybe refugees show up in tau space for sanctuary. maybe they bring tech with them adding to the tau's technology base.

You could use almost any starfaring race for them. How about the Lacrymole from Mark of the xenos? Man, what allies they'd make! Talk about spies and infiltrators.....

There's another alien species in mark iof the xenos that hires out as mercenaries. They are reported to work with the kroot so they may already be known to the tau. The OP asked about water worlds in his post and these guys are pretty aquatic, so they may be something he wants.

BTW, is it just me or are the tau and kroot the only atheist groups in the 40k universe?

It really irritates me that GW hasn't detailed any of the (supposedly numerous) Tau ally xenos other than Kroot and Vespids. But that doesn't mean that you can't- a Tau-centric campaign would really benefit from some new Tau allies to throw your players off balance. If you don't feel up to designing your own xenos from scratch, there is always the time-honoured practice of 're-skinning'- i.e. using the stats of an existing adversary and changing the cosmetic description. Hence you could have Crov'leks, hulking brutes covered in red hair with a single curved horn protruding from their foreheads, recruited from a feral deathworld, who are in fact statistically just Orks (but your players don't need to know that)...

Tau + Squat Alliance!

The pragmatic, hard working squats fit right into the tau empire being settled on inhospitable, high G mineral rich worlds in tau space where they rapidly burrowed in and made themselves at home, paying the tau in mined resources. The squat's superstition free attitude towards technology got along just fine with the tau's views and they had little trouble working with tau engineers and technicians who we're occasionally amazed at the squats almost intuitive technical skills. The squats were impressed by tau technology, especially since the whole race put together didn't have one decent beard among them.

As for squat stats I would base them on lathemasters from dark heresy lathe worlds. Add it a lower movement speed and longer lifespan.

Yeah, tau allies..... I hate to open myself up to 'captain obvious' remarks but what about some of these xenos races the imperium have been exterminating? Maybe refugees show up in tau space for sanctuary. maybe they bring tech with them adding to the tau's technology base.

You could use almost any starfaring race for them. How about the Lacrymole from Mark of the xenos? Man, what allies they'd make! Talk about spies and infiltrators.....

There's another alien species in mark iof the xenos that hires out as mercenaries. They are reported to work with the kroot so they may already be known to the tau. The OP asked about water worlds in his post and these guys are pretty aquatic, so they may be something he wants.

BTW, is it just me or are the tau and kroot the only atheist groups in the 40k universe?

Depends: Do star-gods count? And does killing them make you an atheist? Then maybe Necrons.

Tyranids i guess.

Still it's kinda hard to be atheist if you know what's in the warp (kinda like living on Diskworld.)

Also must be kinda hard to worship if your entire pantheon (except for 2 and half) get's wiped out. Hehe stupid eldar

Yeah, tau allies..... I hate to open myself up to 'captain obvious' remarks but what about some of these xenos races the imperium have been exterminating? Maybe refugees show up in tau space for sanctuary. maybe they bring tech with them adding to the tau's technology base.

You could use almost any starfaring race for them. How about the Lacrymole from Mark of the xenos? Man, what allies they'd make! Talk about spies and infiltrators.....

There's another alien species in mark iof the xenos that hires out as mercenaries. They are reported to work with the kroot so they may already be known to the tau. The OP asked about water worlds in his post and these guys are pretty aquatic, so they may be something he wants.

BTW, is it just me or are the tau and kroot the only atheist groups in the 40k universe?

Lots of scope for custom species. I recall xenos generators from Dark Heresy GM Kit and Rogue Trader's Koronus Bestiary. There are many species which are barely expanded upon in the existing canon: http://wh40k.lexicanum.com/wiki/List_of_sentient_species

Lacrymole seem to be very self-interested, even for xenos. But maybe they'd "ally" with the Tau to screw them out of as much as they can get.

Loxatl?

There are heretics who deny the God-Emperor in human space. Technically many space marines count as they don't see either the Emperor as a god, nor alien idols or the powerful but vile "ruinous powers".