I dont think they have regiments, only security forces on the ship to protect it incase of attack in space..

 

They have "marines" (in the historical sense of armed personell to repel boarders) by the name of "Armsmen". The fluff describes them as typically armed with lasguns,stubbers, shotguns and shotcannons. Specific numbers are never given, just that there are at least enough on Dictator class carrier to pack out a couple of small shuttles. Otherwise to repel boarders the crew improvise weapons as and where they have to. The Imperial Navy though are forbidden to have their own ground forces, thats what the Imperial Guard is for and the reasoning behind that is so that nobody holds too much concentrated military power after the Horus Heresy.

Theres a mention of rebreathers, so you can probably improvise with either cadians or stormtroopers with suitable conversions. Sources are the Battlefleet Gothic & BFG Armada rulebooks and the Black Library novels "Execution Hour" and "Shadow Point" by Gordon Rennie.

 

"Marines" in this context would probably be constrained to a limited number of troops to protect a ship against boarders. If you wanted to model a contingent of these on a 40K table, I'd suggest a squad or two of vets with shotguns and possibly flamers. I would think that at most you might include them as a contingent in a larger IG force.

 

I assume you're referring to "marines" in general, not the Astartes variety. Generally, I think the Navy relies on the Guard for protection against boarding actions, though Navy crewmen can still grab a weapon and shoot things.

 

The Black Library books are full of stories about inquisitors requisitioning naval troops which are outfitted identically to pre-5th Edition IG Stormtroopers (carapace armor and hellguns).

There are also official GW rules floating around for Space Hulk that allow you to use Stormtroopers in place of Marines.

So I'd go with Vets in Carapace Armor with Stormtroopers in support.

 

Indeed, although it will depend somewhat on the ship in question, but almost all carry dedicated Armsmen who pull double duty to repel boarders and enforce order

(Also, it's a Dictator-class Cruiser, not carrier. Having half of your guns replaced with strike craft does not a carrier make).

 

Im sure that its referred to as a carrier at least once in Rennie's books.

 

Perhaps, but this is Black Library we're talking about. In Rynn's World it mentions the imperial fleet having dozens of alpha-grade psykers and the ork gestalt waagh-ness creating a shadow in the warp effect. It might also be an in-character mistake like in the Cain books when the titular character (not having paid any attention to the ships orbiting the world he's on) screws up the class of vessel the flagship is.

 

The biggest ships in Gothic have "Shark" boarding craft which latch onto enemy vessels and cut access points for troops inside. All ships in Gothic can also use teleporters to send troops onto unshielded vessels and sabotage them.
These troops would defiantly be under Navy control.

I don't think they are as versatile as Marines though (real Marines, not Space Marines). Marines can conduct land operations just as effectively as other troops. They're like the airborne of the seas. I think these Navy troops would be more like SWAT teams or riot police (with lethal weaponry). Very much equipped and trained for a very specialised type of role, great for it, but not much use in general warfare.

Having said that, I love the art for them:
http://wh40k.lexicanum.com/mediawiki/images/b/b1/Fleet_LandingCrew.jpg