Backspacehacker wrote:
Probably better suited for the background forms, that said....

You probably wanna look into rouge traders, they are more or less the "Explorers" of the imperium. Most of those fleets are pretty self sustaining, however like any ship, they still need to dock/resupply every now and then.

Mechanicum fleets if i recall do have forge ships, which are basically flying manafactoriums able to produce ammo, guns, weapons, armor, vehicles ect ect, but at a much slower pace but they contain all they need to go from raw resources to finished products.

chaos0xomega wrote:
"Self-sustaining" implies a closed system (i.e. no inputs from outside the vessel/fleet) that has the ability to remain "at sea" indefinitely, with no need to return to port or engage in replenishment operations to maintain food, water, fuel, oxygen, and other supplies and stores. Imperium vessels and fleets are... not that, and while some may be able to operate in isolation for long durations, eventually they do need to replenish, whether it be via piracy, trade, tithe, or foraging, etc.

Now, if you're looking for something capable of extended or long-term "independent operations", i.e. the ability to operate without needing to return to port over an extended timeframe, then thats a slightly different story. In terms of individual vessels you're probably looking at something more along the lines of a cruiser or a rogue trader merchantman, something that is of sufficient size to carry large enough stores to maintain itself and its crew over a longer timespan (but not so large as a battleship that it ends up on the wrong size of the efficiency curve due to excessive crew demands), while being well armed/armored/equipped enough to engage in piracy and/or foraging operations to replenish its own stores while operating out of reach of replenishment fleets and storage depots.

Fleetwise, it kinda depends, larger and smaller warships tend not to be able to carry enough stores relative to their operating and crew requirements/demands, "mid-sized" vessels like "cruisers" (within the context of 40k terminology) tend to exist at or near the optimum on the efficiency curve where the crew requirements are balanced vs the size of available stores, etc. As your fleet grows in numbers of battleships/destroyers/frigates, etc. you will generally need to offset the inefficiency of those vessels with non-combatants such as freighters and bulk cargo transporters which tend to have minimal crew but very significantly large stores (and are thus most efficient in terms of crew:supply ratio). Generally, you will need vessels for fuel, food, munitions, water, oxygen, parts and consumables, etc. Depending on the size of the fleet, this may be one vessel transporting all of the above, or one or more dedicated vessels for each of the above. Warships will probably tend to have limited capability of recycling water and oxygen, and probably can also "make food" by recycling dead bodies into corpse-starch, but that will only get you so far. Its possible that a large enough fleet might have dedicated vessels to recycle water/oxygen etc. to supplement other vessels, particularly if the fleet includes "civilian-grade"/shorter duration vessels that might not have the capability to do so themselves. Additionally, if you have people movers (i.e. personnel transporters and troop transports, etc.) you will probably also need dedicated freighters and cargo vessels in order to carry additional food/water/other supplies to supplement the on-board stores which will most likely be only enough to cover short-duration transits. Likewise, if theres a significant enough population of personnel and passengers on a long-duration journey, you will likely want one or more dedicated medical/hospital vessels in order to provide medical services for the wounded, ill, and injured, as well as to transport medical supplies beyond the limited triage capabilities that ships might have on board. A warships medical facilities might be able to treat limited numbers of wounded and handle typical illness/injury, but if you are expecting significant battlefield injury or you're on a multi-year journey and expect the fleets population to give birth or potentially have to deal with the emergence of more serious illness like cancer or degenerative diseases, etc. you might need more dedicated facilities with specialist personnel and equipment. Its possible to that you might have dedicated hydroponics/greenhouse vessels that are able to generate produce and/or process livestock, and with the tendency of 40k to have things like space whales and the like you might even have meat-processing vessels capable of harvesting and processing voidfauna to supplement food stores - but you probably won't be able to rely on them exclusively to supply the entire fleet for an extended duration.

Honestly, watch Battlestar Galactica (the reboot from the mid 2000s), probably will give you a few good ideas.

PenitentJake wrote:
I know you're looking for background info, but I always liked drawing connects between rules and fluff.

On that note, GW has printed some interesting rules for fleet-based Crusade armies. White Dwarf did an article on the torchbearer fleets, which went out to deliver Primaris troops as replacements for Chapters that had taken heavy losses. So these were mixed Space Marine, Custodes and Mechanicus armies.

Then the Vigilus alone book deals with wars of faith, which combine guard, sisters and marines.

I'm also reminded of the Ecclesiarchy Missionaria Galactica fleets that set out to find the far reaches of space and spread the imperial creed so that the civilizations that they encounter are prepared when Imperial armies arrive- the idea is very Dune based- if you've reach the books or seen any of the movie versions, you know that the reason the Fremen helped Paul and his mom is that the Bene Gesserit seeded the planet with myths that Paul and Jessica were able to exploit.

Because these fleets are bound for the furthest reaches of space, venturing into basically unknown territory, they have to be somewhat self sufficient.

Finally, sisters definitely do have cathedrals and places of worship on their ships, and they do have vessels that have been with them for long enough that they can be thought of as Sororitas vessels, even if they are officially still listed as assets of the Imperial navy.

PenitentJake wrote:
Vigilus Alone, the new Nachmund Campaign book is the one for Wars of Faith (Sisters + Guard + Marines).

I only recommend the book if you already play, and have the other stuff you'd need- 40k is expensive, and getting more expensive, and the amount of pages that specifically deal with these types of armies are relatively few, Here is a link to the Goonhammer review of how the rules work- for story writing purposes, this might be all you need to satisfy your curiosity.

https://www.goonhammer.com/war-zone-nachmund-vigilus-alone-the-narrative-play-review/

As for the Torchbearer Fleet rules, because they are in a White Dwarf, they're cheaper, but it's an older Dwarf, so it'll be harder to find. If GW get's back to publishing annuals again, there is a good chance these will be included- it's some of the coolest White Dwarf content I've read this edition. As it turns out, the Goons have a review of this too:

https://www.goonhammer.com/white-dwarf-466-flashpoints-and-torchbearers-review/

Note: If you are already a subscriber to WH+ I think this Dwarf can be found in the vault. Note: This is not necessarily an endorsement of WH+ either- much of the WH TV content is good, but there isn't as much of it as many people hoped. It is the exclusive minis that help make WH+ worth it's subscription price and quite a few Dakkanaughts might even dispute that. But if you are already a subscriber, you should already have access to this Dwarf- it's issue 466.

 Kid_Kyoto wrote:
The Gods of Mars trilogy is all about an Imperial All Stars fleet going into the grim darkness of the unknown.

It was uneven (book 3 is basically seeing how many different ways you can say 'the heroes smashed the evil robots') but it does give a feel for what the Imperium can do. The description in book 2 of them landing to check out a planet is worth the price of admission.