Hello fellow DH players and GM's! first post on the forum

Im thinking of running a game set on a large space ship, like a battleship of the imperial navy, as they have always fascinated me, i mean, its a 7 kilometre long spear of steel, with the power to destroy a planet in a matter of hours.

The players will be on their way home from some other mission, and have been accepted on board for a reason yet to be determined.

while traveling on the ship, they will notice strange things happening, hear rumours of weird shadows on the lower decks, stuff like that.

Being agents of the imperial inquisition they will of course investigate the rumours when they start to become disturbing (and real!) enough.

Im thinking of having a cult run by some pretty high ranking people on the ship, and I'm toying a little with the idea of having the master tech priest or whatever he's called actually being a member of the Dark Mechanicum and him having some diabolic plan about sacrificing the entire ships crew or some other suitably evil thing.

I am quite well versed in 40K lore, but i need some additional inspiration, does anyone know about any books that have details about:
A: Imperial space vessels.

B: The Dark Mehcanicum.

You are of course more than welcome to input your own ideas as well! (well, please do that actually )

I'm assuming you've already read the Horus Heresy series that details how the Dark Machanicum was formed? They have a pretty interesting story. Regardless, they are splintered from the AdMech and I am under the impression that people don't generally move from the AdMech to the DM. The DM supports titan legions and helps create weapons for chaos forces from the Eye of Terror. There are certainly AdMech who are corrupted by their thirst for knowledge, sometimes forbidden, and who are willing to carry out terrible plots if it will advance their schemes. Perhaps there is a cult worshiping chaos, who has been trying to corrupt the tech priest by promising him tantalizing bits of forbidden knowledge, access to warp-infused cogitators or artificial intelligence. The DM are an interesting lot, and if they do show up here perhaps it could be as a stowaway instead of a corrupted member of the AdMech. In fact, maybe there's a DM member who's been creating a band of hereteks who use twisted technology to build a growing cult in the shadowy underdecks. Perhaps the DM has even recruited members of the AdMech on the ship to aid him.

As for information about the ships? Well, the obvious place to start is Rogue Trader… The core book and the Battlefleet Koronus book are both great for getting a feel of what these floating cities are like to live in.

In addition to the Rogue Trader books mentioned, another nice resource are the (free to download) Battleship Gothic rules from the GW website, which has a lot of nice pictures and some descriptions of the different classes of ships. I would definitely start with the RT stuff first though, it's generally nicer and much more recent, but the BFG is a good free alternative.