I was thinking that it could be interpreted as the Marines knowing they don’t make a difference. It reminds me of this quote:
Dr. Nefarious: “To think, they called me insane, Lawrence. We’ll see who’s insane when my [mutant armies] have exterminated all life on this miserable planet!”
Lawrence: “That should clear things right up, sir.”
I was thinking that it could be interpreted as the Marines knowing they don’t make a difference. It reminds me of this quote: