What I find interesting about WWII music is the differences between US and German subject matter. Perhaps I have just been looking in the wrong places but here is what I have noticed:
The german music I have heard is very militaristic (no suprise there, of course.) There are marches and songs for every possible military arm or type of unit, eg. "Stuka Vor," "Panzergrenadier Leid," "Torpedo Los!," etc. (You can see a lot of these here: http://ingeb.org/WWII.html) Are there similar US songs other than the Armed Forces songs? I don't recall hearing of a "Airborne Song," "The Infantry Song," "Submariner Song."
The American music seems to be more focused on relationships, the situation back home, and the effort to win the war as opposed to the specifics involved in winning it. I also don't see a lot of the German songs dealing with these issues (Lili Marlena not withstanding.)
You would figure that both types of subject matter would be common on both sides of the conflict.
Todd O