The "Last Man?"

The first time I watched this movie I noticed during the mission to "rescue the kittens and smash the guns" that WarDaddy was suddenly wearing a standard M1 Army helmet over top of his tankers helmet. I originally thought this was some sort of strange continuation error, but when I watched this scene again I realized that just before the assault, after he orders the men off the tanks, he says "give me the Last Man" and we seen him pick the M1 up off the hatch. It's easy to miss because it's such a quick, almost throwaway line, right before the scene immediately cuts to the tanks smashing through the hedgerows.

My question is does anyone know who/what this is in reference to? I gather it was some sort of symbolic gesture, perhaps honoring a fallen soldier(s), but it struck me as an odd detail to just toss in without any sort of specific backstory or explanation (unless I missed it). Was this something real life WWII tankers were known to do? Any insight would be appreciated.