One of the weapon systems that amazed me was "schräge musik", cannons on the back of the aeroplane like Me 110, and as you in nachtjagd flew under the allied bomber you shot it in the stomach. This was often dangerous to the german pilot as well, as the bomber might fall on the german plane. Yet this is quite ingenious stuff as the allied pilots wouldn´t see you easily as you were under it ( B17 one of the exceptions? ).
See one site covering this:
http://www.geocities.com/CapeCanaver...n/fgun-uf.html