Do you mean the Soviet forces? If, yes, then it was the 23rd of April, 1945 during the Battle of Berlin in World War Two, but keep in mind that the Codl War hadn't started yet on that date.
If you're doing Germany as your national study, I'm not sure if an assessment on the Soviet occupation of Germany is relevant. Unless you are somehow referring to the Spartacists and Communist Party between 1919-33.