The Führer Headquarters, Führerhauptquartiere abbreviated FHQu in German, were headquarters used by Nazi leader Adolf Hitler and his close circle of commanders and officials. As Hitler directly controlled much of the German war effort, the FHQu were de facto military headquarters. At the beginning of the war, Hitler's railway train served as Führerhauptquartier, for example during the Balkans campaign in the spring of 1941, but the construction of Führerhauptquartiere, Hitler's Headquarters, was entrusted to the Organisation Todt, the Nazi civil engineering body. 'Wolfsschanze' in East Prussia is well known, not least because of 'Operation Valkyrie', Oberst Claus von Stauffenberg's attempt to kill Hitler by detonating a bomb under a conference table on July 20, 1944\. It was one of the largest Führer headquarters, and the one where Hitler remained the longest period but by the end of 1944, 16 headquarters had been built throughout Europe and three more were still under construction. Many were never used.