Okay, the feel I want from my Marine games is basically Pendragon. Marines are knights clad in shining Powered
Armour riding forth on mighty motorcycle steeds to quest and rescue beautiful damsels in distress.
So, adapting Pendragon adventures to Deathwatch, part the first:-
The Adventure of the Questioned Heraldry
While briefing and re-equipping at a non-Deathwatch Marine facility the player Marines encounter an argument. Two Marines from different chapters have discovered that their armour is decorated with an almost identical device - crossed powerswords on a field of skulls (one has the swords hilt up, the other hilt down).
Brother Banast of the Imperial Fists is incensed, and demands that Brother Fogolor of the Dire Wolves either give up the arms or face him in battle.
As a neutral party the player Marines are asked for their opinion.
Have the players make a Lore (Marine Heraldry) roll for their Marines.
On a success, the Marines know that by custom the arms of different Marines must not be the same, but that these are not identical.
With three margins of success, the Marines knows that these two devices are too similar to be considered different.
If the consensus is that the arms are different, the Marines are satisfied, but if they are judged the same the Marines take to the field to settle the dispute by combat.
Have two players take control of the Marines and fight to the death!