Definitely the Red Army had started to use some of the Blitzkrieg methods in their offensive system but I think "maskirovka" that is masking the main attack from the enemy truly worked here. Hitler did not believe the attack would come to Berlin in 1945 (?!) and in the summer 1944 the Red Army attacked "in the wrong place" as well.

The fortifications did keep big numbers of Red Army men tied to them but Stalin had troops to use while Hitler did not.

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