Technically, the term "Space Marines" would apply to any army that fights in ship-to-ship actions. Also, the term "Grenadiers" applies to any army that uses Grenades. I don't think it would ever matter to me (or any sane player) how you name your force.
You'll forgive me, but you must be mistaken. I've met your makers, and they don't even know your name...
GIVING CHASE- ORDO HERETICUS FIC (Updated Mar. 19)
Hat in the Ring