Operation Clausewitz was part of the defence of Berlin by Nazi Germany during the final stage of the European conflict of World War II. Hitler ordered Fall Clausewitz on 20 April 1945 which called for a number of unknown actions but did include the evacuation of all Wehrmacht and SS offices in Berlin and the destruction of official papers and documents of the state. After this operation was initiated Berlin became a front line city.
There is no information today regarding the details of Operation Clausewitz.
While Hitler is not seen announcing Operation Clausewitz in Downfall, it is implied that he did it soon after he talked on the phone with Karl Koller about the Soviet shelling that morning. At the time Himmler and Fegelein enter the hall in the Reich Chancellery the operation is already in effect. Fegelein mentions it to Himmler, and the latter replied that that makes Berlin a front line city, but Hitler won't be able to hold it for long.
After that a government building is shown being emptied of all documents, which were thrown out the window and raining down onto the street level. Someone is heard giving orders that they're leaving in two hours. Ernst-Günther Schenck, seeing the commotion asks his adjutant of what's going on to which the latter replied that "Clausewitz" is in effect, and that all government departments and the Wehrmacht offices are leaving Berlin. The dissatisfied Schenck went to meet Tellermann who is overseeing the move in order to obtain a permit to stay, so that he can help the remaining civilians.
Later still Himmler talks to Fegelein about heading north, with a covert objective of negotiating surrender with Eisenhower. It is unsure if his move north is part of Clausewitz, as head of the SS.