Hey all, I've just recently started running deathwatch for my players. I'm a experienced GM so I'm going to shoot for big things with big scope after running extraction. The problem I hit was I had some new players comign in and needed to get some new troops online without sending the members back to Fortress Enioch since I wanted to do somethign with the last hours of Tantalus. Advice on tweaking the scenario is appreciated or advice on running mass combats short of breaking out the regular 40k rules. I figure i'd do some abstract stuff with leadership tests and the like. Also since i'm a relative newbie to the 40k universe advice on tweaking the scenario to fit the setting would also be helpful with the caveat that I'm one of those GM's who will gleefully mangle the setting to tell a better story.

The defense of Fortress Repentant
Narrative Goals:
Shuffle in new PC's, including sisters of battle.
Allow the killteam a chance to strike a blow at the Tyranid fleet in the Castobel system and prevent them from absorbing Tantalus biomass.
Introduce the Omega Vault.
Introduce the players to the scale of 40k conflict.
Opening Salvo:

The kill team has returned to the Thunder's Word after a successful mission on Tantalus. The apothecary will want to immediately take the Magos into surgery and get him restored to some semblance of his old self. I'm thinking this will involve a plus +10 medicae roll (the roll is rather difficult but the Thunder's Word and the Magos own implants make this easier). During this time the ship will have to fight it's way out of lower orbit and slip into the debris field in high orbit. I plan on running this as an abstract space battle but it will result in at least one boarding action pitting the tactical marine (who's player wants to sub out for a sister of battle) in a pitched battle with a tyranid creature. Ideally her character will defeat the creature but narratively will be mortally wounded in the process. This will also allow me to show the players the heroic sacrifice rules as well as show them how squishy they really are.
Once the ship is safe and playing cat and mouse in the debris field the players will be approached by Keeper-Captain Pallas. While the fighting has been going on the ship's astropath has sent a message back to Enioch updating them on the status of the killteams mission as well as passing on the results of messages from the planet/system. The kill teams own success as well as one last hard point has delayed the death of the moon by hours if not a day (they blew the fuel depot up in the swarms face). The mention of the name of the last hard point on the planet, the Fortress Repentant has triggered something in the Omega vault. It has revealed a schematic indicating the fortress is actually the very tip of a planetary terraforming structure which might be used to destroy the planet. According to Ordo Xenos records it should contain a working (though forgotten) teleporter and a dark age set of terraforming gear that could be used to destroy the planet.
Further complicating matters is a detachment of black templar chapter marine's making their last stand at the fortress after they were cut off from their own extraction. The kill team's primary mission will be to get the geneseeds of their fallen and any irreplaceable relics at the fortress out.

Sneaky GM stuff:
The adeptus mechanicus have sealed the lower catacombs of the fortress off with a powerful energy shield. They fully intend to sacrifice their lives and die on the inside of the terrforming mechanism in order to keep it sealed to ensure the xenos don't breach the catacombs. Even getting in will require fighting or reasoning with the tech priests and tech guard. The big kicker however is the vaults can't even be open without a massive power drain being placed on the system such as the teleporter. Effectively the players will have to miss the last bus to play in sudden death overtime.

Mission Objectives:
Primary Mission:
Primary Objective: Effect Extraction of the Black Templars geneseeds and any living members.
Secondary Objective
Stabilize the battle lines: By the time the players arrive things are looking dire at the fortress, they'll need to come in via drop pod and then have a running fire fight to get to the fortress via land speeder. The PC's within the fortress will have an important part in getting them in successfully. After this it's a pitched battle as the Tyranid's make a push on the fortress.
Secondary Objective: Deny the planet to the enemy: Enter the underground structure and fire up the terraforming gear.
Tertiary Objectives: Survive or win honors in the space assault.
Other stuff as appropriate
Unbeknowst to the players firing up the terraforming gear isn't an actual death sentence although it will be hard for them to tell that on the groun unless their attentive. When the terraformers go active the fortress will actually be shielded and sealed.

Well it looks perfectly ok with me. The only thing I would possibly comment on is the mass combat. I would probably not rule it like that at all but instead but the PC:s in the most important position and let things depend on them. If they hold back the Tyranids then they battle is going the Imperium's way, if they don't the Tyranids drives the Imperials back.

adventure sounds perfectly 40k to me....maybe might wanna put one extra unforseeable badthing in the catacombs....something the xenos terraformers left behind in their machine...or one of the original makers in stasis...or some such...if you want. Perfect ending, btw: heroic sacrifice with no chance of survival (yet thanx to the machinations of the ancient xenos, the marines survive! thank the Emperor or thank the xenos?)

Thanks for the inputs.

What I ended up doing after some serious deliberation was actually going a lot darker as I really wantedt o plug my players into the Warhammer mythos and how it's ever changing history might affect the present. I decided that the fortress was a Word Bearer's chapter keep set up and then left in stand down mode from just before they were all recalled to be rebuked and before Logar fall to chaos. At the core of the fortress tied into the machine's the run the terrforming gear they'll find a Word Bearer's dreadnaught in slumber that they'll have to rouse to activat the planets chatechism. They will also find that someone has been into the fotress just a little over 70 years before them and stolen a collection of the geneseeds stored there. This will tie into one of my players playing a newly minted female space marine as unbeknownst to her they were generated from Word Bearer's genestock.

I also plan for the Word Bearer's to play heavily into the Dark Pattern in my campaign should it go long enough.