I have
the 3rd Edition board game, which this game is based on. 600 years prior to the events of the assault on
this Space Hulk,
the Sin of Damnation, the Blood Angels lost 95% of the Chapter in an ill-fated assault on a Space Hulk that drifted into the Secoris system. The Chapter considers this mission a kind of chance of regaining their honor (and revenge) of sorts.
As for the standard of loadout of Terminator interdiction squads, do take note that the standard Storm Bolter + Power Fist configuration is more than enough to take care of the threats found on Space Hulk 90% of the time (mostly pirates, mutants, or orks). Plus standard power weapons can't tear up meter-wide bulkheads or other impediments.