This was an idea I have been trying to do for a while and was looking for ideas from the community, anything you can add or correct would be greatly appreciated

I would like to add a contingent of space marines to a rogue trader house/ship like in the old (1987 RT book) where you get to roll around with a hundred or so of them (remember box of 30 RTB-01). I run a very rogue trader “era” style wh40k game I try to express that the imperium as struggling, decadent and generally falling apart imperium that the books allude to. Space is vast and the imperium does not have the control that books some time make it seem, and not even in the zones of control that they do have. I don’t really go to crazy with the dystopia style either (yeah I love grim dark, but it gets old). So here are my question and musings. I’m also assuming that the marines are all in the RT ship or ships. and the players go on 10 to 30 year sojourns into the unexplored space (which is pretty much everywhere) which could mean 30 to 200 years away from imperial controlled space .

1. A whole company gets the honor of going where no man/xenos/ad-mech has gone before with a rogue trader, thus fulfilling an ancient pact. According to one of the RT books a primarch could have signed or cosigned the warrant of trade.

1. Does the company or so of space marines get written off and are consider heroes by their chapter and dead or at least MIA?
2. Does the Chapter use this as a way of getting rid of troublesome SM?
3. Or does the chapter still count them as part of their 1000? And what happens if they don’t return?
4. Would the chapter do this to benefit itself by sending a hundred marines in preparation to a crusade, they would send these guys off and be written off as heroes and then when they returned a few hundred years later or after the chapter has suffered some losses, rejoin the chapter and boost their numbers back up to 1000 or close to it?
5. Would the RT be responcible in bringing back the gene-seed and equipment of the fallen?
6. Would the hundred or so space marines be able to recruit while with the RT? Or even replace their numbers?

1. From what chapter would the Astartes be from?

1. I was looking at Ultramarines but they seem to vital and important to just get a hundred or even a few I imagine they would tell you to go to any of their successors and get from them?
2. I’m not sure if I remember correctly but weren’t their chapters that were specifically created to go with rogue traders? (if so, do you remember where that was written?)
3. I was also thinking of a mix of different chapters including ones with extreme dislike of the xenos like Black Templars (if they can do death watch then they can put up with rogue trader) and add lots of drama to the RT’s boat.

1. What would there equipment be like?

1. I was thinking of keeping the RTB-01 style and say that the marines would get a recently made corvus Mark VI armor and they have permission to add their own glory to on the armor. If they survive.
2. I imagine they would get all new equipment and maybe very few relics?

Well this is what I got and its late. (for me)

1. Does the company or so of space marines get written off and are consider heroes by their chapter and dead or at least MIA?

Space Marines are expensive. You signed for them, you're expected to return them in the same condition they were issued.

Of course, if you don't come back, not your problem.

Essentially, it would be a formal detached duty.

1. Does the Chapter use this as a way of getting rid of troublesome SM?

Possibly, but unlikely. The Deathwatch is a great way for quietly shuffling oddballs off to one side, but if you're being provided with a detached company - it's highly unlikely the chapter has an entire company of [insert expletive] - unless they're the Fire Hawks or Marines Malevolent - and few chapter command cadres are arrogant enough to exile an entire company just because they don't like the captain (Otherwise the Ultramarines 2nd would be on a Rogue Trader expeditionary fleet soooo fast they wouldn't have time to blink).

1. Or does the chapter still count them as part of their 1000? And what happens if they don’t return?

If a whole company as a 'proper' formation has been detached, captain, command squad and all, then it still exists and would be treated as such. If and when the chapter has reason to believe the expedition has come to grief and been wiped out, then and only then would they consider raising a new company. Templars or Wolves of course, and similar chapters, wouldn't care and just keep recruiting.

1. Would the chapter do this to benefit itself by sending a hundred marines in preparation to a crusade, they would send these guys off and be written off as heroes and then when they returned a few hundred years later or after the chapter has suffered some losses, rejoin the chapter and boost their numbers back up to 1000 or close to it?

See above.

Note that the '1000-man limit' is policed but not too strictly. It's not unheard of for chapters to exceed it during periods of intense conflict, where lots of companies are deployed and detached forces are going everywhere. This is why no-one realised at first how big the Astral Claws had bulked themselves up to. Doing it deliberately is grounds for inquisitorial pokings and they're expected to sort it out sharpish once peace breaks out, though.

1. Would the RT be responcible in bringing back the gene-seed and equipment of the fallen?

Hell, yes. If you make it back, and you abandoned the geneseed of a fallen company - a tenth of the chapter - out there in the darkness beyond the imperium, you'd better have a bloody convincing explanation. Equipment, the same, but less so (unless you've been given any chapter relics).

1. Would the hundred or so space marines be able to recruit while with the RT? Or even replace their numbers?

You'd have a company apothecary, but recruitment.... I wouldn't think so. Unless you're talking black templars with their master/apprentice style training, training facilities means the tenth, and the primary apothecarion of the chapters fleet/fortress. I wouldn't be surprised to see the company come with several attached scout squads, and see several of them promoted to full battle brothers (taking the armour of casualties) over the course of the expedition, though.

1. From what chapter would the Astartes be from?

One that the Rogue Trader has a very good relationship with! On a more serious note, one with an open-minded nature about working with 'lesser mortals' (so not Dark Angels) and one with no specific strategic responsibilities that they can't abandon (so probably not Astartes Praeses from the Eye of Terror garrison force - like the White Consuls).

Ideally fleet based.

The 'classic' chapter for Rogue Trader expeditions are the Marines Errant, who apparently do detach forces to Rogue Trader Expeditions all the time (particularly one called House Ecale), or a pragmatic bunch who tend to zip back and forth across the galaxy like the Raptors, who seem to be openminded enough that they wouldn't be up in arms if you actually talk to a non-imperial world before invading it...

If launching a much more....militant....crusade out beyond the Imperium, the Black Templars have essentially kept the Great Crusade going for 10,000 years and would be happy to sign on for the promise of a good xenos-purging.

The last possibility - which is in some ways most likely, because it involves political pull with the High Lords, not the Astartes, is a newly founded chapter. There have been a few recently founded chapters - The Sable Swords are the most recent chapter explicitely mentioned but you could always come up with your own recently founded one. A recently founded chapter would have new, uniform equipment and few relics (hence the 'corvus company') and have reserve companyes - maybe even battle companies - essentially untested in battle, which, as part of the centuries-long process of a chapter founding, the Rogue Trader might be able to have serve in his expeditionary fleet.

1. I was looking at Ultramarines but they seem to vital and important to just get a hundred or even a few I imagine they would tell you to go to any of their successors and get from them?

They don't controll their successors, but I would doubt you'd get a full company detached from them. The main problem with the ultramarines is that they hold responsibility for Ultramar - a couple of sectors by anyone else's standards - which they provide the main security for, and which - whilst not continuously 'under threat' in the same way cadia is, is sandwiched between one of the largest known orkish territories in the galaxy, the tau empire and the eastern fringe (currently tyranid central).

Fleet based chapters, by comparison, can 'peel off' a company squadron from the fleet that's essentially just trolling around the galaxy at large to meet up with an expeditionary fleet.

1. I was also thinking of a mix of different chapters including ones with extreme dislike of the xenos like Black Templars (if they can do death watch then they can put up with rogue trader) and add lots of drama to the RT’s boat.

If you read the background of the 13th black crusade (I think?) there was something called the 'Ultramarines honour company' - not an ultramarines company as such, it was a company sized formation consisting of squads from lots of different ultramarines successor chapters; because none of them could afford to send a full company but couldn't be seen to ignore such a massive threat to the imperium. If yon rogue trader has that kind of pull, then it might be a more realistic way to assemble a 'company'; from a first founding chapter plus several successors.

1. What would there equipment be like?

Depends on the company. If you've got a company strike cruiser with company aboard attached to your fleet, then anything in a standard marine arsenal - save relics like chapter standards and suits of terminator plate.

For a 'patched together' company - I'd assume kitted out in the fashion of a tactical company; simply because a tactical squad is the most likely thing for any individual chapter to send. As noted, also patch on a couple of scout squads - trainees seeking seasoning and potential replacements. The force would come with it's own interface craft - stormravens and/or thunderhawks, again from a mix of chapter fleets. Armour is probably less likely as it's less useful without the strike cruisers and landing craft to deploy it. Irreplaceable stuff like terminator plate and dreadnoughts certainly wouldn't be offered.

You might also note that, much like the IG's tanks, Space Marines are not really the stand-alone force they are often shown as. When a group as large as this goes, even if they don't bring their tanks, which in your setting might still be the IG's tanks , they bring tons of people with them, including Chapter serfs, Tech-Priests (need to know the Astartes stuff, and Techmarines often need help), and such. I'd almost require that they would also bring a few of their own Astropaths. In this way, they could stay in contact with their parent Chapter, who wouldn't feel it quite the same write-off as just giving you a Company.

I can see a few bonuses, too. Boarding actions against you could be a joke, while you could have SM boarders to make your life easy. Crew morale would also reflect demigods walking on your ship. Having the drop pod stations and craft docks would also make sense, so their thunderhawks and drop pods work.

Not sure on a specific Chapter, but any fleet-based would PROBABLY work, if you can get their Chapter leadership to like the idea. In a story of mine, the very old Warrant is actually marked with honours of the Raven Guard, from ages ago. While it wouldn't get Korvallus a Company (you might argue that there aren't that many Raven Guard left), it could get help/assistance from them, and perhaps the use of a squad or two, if they needed transport someplace, and let's be honest, if you aren't playing Deathwatch, two squads of Space Marines is probably enough for anything. I don't know if they were a real good fit, but his organization is the Silver Ravens, and I do like some of the stuff that the Raven Guard do. Also, they could be on hard enough straits to require them to seek assistance in things, and thus offer it in return.

You'd have a company apothecary, but recruitment.... I wouldn't think so.

Hmm, in the White Dwarf Index Astartes series it was mentioned to work for the Relictors:

"After the Inquisiton censured the Relictors for the actions of Inquisitor De Marche, the Chapter lost its feudal rights to Torva Minoris, which meant they could no longer recruit from amongst its feral tribes. The Relictors were forced to gather potential acolytes from amongst the populations they encountered during their penitent crusade. The Inquisiton has ruled that no Aduptus Astartes Chapter may recruit from Torva Minoris, and it is believed the Ordo Malleus keeps a close watch on the world to ensure its ruling is adhered to."

I would expect "mobile recruitment" to be severely limited, though, and even less reliable than at their home base. Given that it takes about 10 years to turn a kid into a Space Marine, it may also well be possible that it is not deemed worthwhile for an excursion that lasts "only" 20-30 years. Whilst I believe it possible to store the necessary facilities for limited Marine recruitment aboard a RT starship (operating room, lab with stasis containers and cultivation chambers), I suppose the delay (the first replacements would enter service about halfway to completion of this tour) would render the effort questionable ...?

Maybe the company would rather just be very, very careful in where and how they help out - never committing to bear the brunt of a fight but merely sending one or two squads to support the Rogue Trader's troops whilst the rest stays behind to hone their abilities and recover from injuries they sustained in prior engagements. Essentially them cycling through the troops they have available, like a miniature version of standard Chapter organisation, where, instead of sending individual Battle Companies reinforced with elements from the Reserve, they send individual squads occasionally reinforced with specialists? Just a theory/idea, of course.

The main problem with the ultramarines is that they hold responsibility for Ultramar - a couple of sectors by anyone else's standards

... or seven inhabited planets in eight systems, going by GW's own writing.

Still, the Ultras have more than enough on their hands. Tyranids, Tau, not to mention a dozen other engagements all across Imperial space. I, too, would suggest a "less active" Chapter whose Marines would not be missed as much - unless OP's group is fine with disregarding the various bits of background on the Ultramarines in this matter. Absence of canon means they can make up almost anything they want, after all.

Recruiting by astartes "on the move"? Possible, assuming they have a sufficient stockpile of geneseed, and a sufficiently well-equipped medicae facility. If they've brought their own craft to join the Rogue Trader's flotilla, then you can almost take that as a given (well, maybe not in the case of the smaller RSVs, but almost certainly if they are bringing a Strike Cruiser or bigger), otherwise they're obviously going to be dependent on the facilities the Rogue Trader has on hand (actually, it may be worth the RT negotiating to have the Medicae decks upgraded to apothecarion standards specifically for the astartes, and he may even be able to get them to "pay" for it. That way, if and when the astartes are returned to their chapter, the RT still has a massively upgraded facility, which should make it easier to contract further astartes to join their voyages, and will likely be useful for many other things).

I should note though, that unless you/they're prepared to do some very questionable things (think 21st Founding, or the accelerated growth the Raven Guard used), and/or have an absolutely massive stockpile of geneseed entrusted to the Apothecarion contingent, no force as small as a company is going to be self-sufficient in terms of recruiting- normal attrition rates, along with wastage in geneseed recovered and failed recruits mean that any stand-alone group of astartes, working solely from their own resources, need at least 300 or so to maintain a viable pool of geneseed in the long term and not gradually die out.

Of course, since the company is merely "borrowed", and is likely to return to the chapter at least every subjective century or so (if only to resupply and refit), this isn't likely to be too much of a problem