It doesn't focus on Germany exclusively, but you may find my answer regarding Pius XII and WWII to be of some help on the Catholic side of things. The biggest revision I would make to it is to add that Ventresca's Soldier of Christ: the life of Pope Pius XII is the single book I can unreservedly recommend on the subject.

As always, followup questions from OP and others are encouraged. Also, other posters are encouraged to answer OP's question regarding specifics in Germany itself.