It was at the Bendlerblock that Stauffenberg and Major General Henning von Tresckow secretly modified the Wehrmacht "Operation Valkyrie" plan for the suppression of a possible revolt into a scheme for a coup attempt upon an assassination on Hitler. Stauffenberg's position gave him direct access to situation briefings in Hitler's Wolf's Lair headquarters in East Prussia. On 20 July 1944, he set the fuse of a bomb there and immediately returned to Berlin.[4]