The British were bombing Berlin, albeit certainly not very effectively at the beginning, from August 25, 1940 onward.
Is a *really* lucky bombing possible prior to Barbarossa, where a bombing wipes out a speech by Hitler to a large audience including the entire Nazi hierarchy above the level of Gauleiter?
I'm trying to come up with a of a situation where the Wehrmacht takes over Nazi Germany not because they have assassinated Hitler but rather because they are the only real power left in the Third Reich.