This movie is a lot of fun. Howard Hughes is not amused by the Nazi plan. And really, if you have a rocket pack during WWII and don't use it to kill Nazis, there's something wrong with you.
Joe Johnston, were you so afraid that the audience would side with the Nazis that you made your fictional Nazi propaganda show them as ominous aggressors?
None of those Rocket Nazis have any weapons!
What are they gonna do just walk up and ask people nicely to surrender or else they'll fly around in the air in circles menacingly!?