>>96019903
>How does MkIV destroyers explain the usage of the hard vacuum modification?
It's called "Void hardened" in the HH or just Hardened or Heavy armour, and it's how Destroyers get extra protection against NBQ stuff. FW may have based their design in the Index Astartes art, but that was 15 years ago and 10 after IA.
>Don't DG have their very own gas mask head
That's just a DG mk4 variant, straight outta Visions and Crysos Morturg