In Berlin - Gathow exists a new Air Force Museum.It is managed by the Luftwaffe der deutschen Bundeswehr. I think there are some aircrafts from WW1, Fokker DVII...
In Potsdam you have to visit Schloß Cecilienhof where 1945 the Potsdamer Conference took place. In Potsdam moreover is the "Ständige Ausstellung Luftschiffe in Potsdam". From 1914 - 1916 sixteen Zeppeline were built here for the Imperial German Army and Navy. In Berlin - Karlshorst you can find the Deutsch - Russisches Museum. In this house Generalfeldmarschall Wilhelm Keitel signed the surrender of all german forces on 8.5.1945.
In Berlin - Treptow you should visit one of the greatest soviet war cemetery with a very huge memorial.
Hope that helps.
With best regards, Immo Frese
Nec aspera terrent!