I found this bit of fluff on Black Shields delightfully subtle:
"...the case of a Watch Commander named Israfil. This dour warrior led his forces against a myriad of foes for over three decades, before he was lost on a mission he attended in person, against the pernicious Mire. Despite the rapid intervention of a substantial battle group from the Dark Angels Chapter, Israfil's body was never recovered..."
I'm guessing Israfil's "body" is somewhere in the catacombs under The Rock.