acutely aware that the Soviet Union was bearing the brunt of the war against Hitler, and were aware of Stalin's constant suspicions that they were doing deals behind his back. They thus refused any discussions that might be seen as suggesting a willingness to reach a separate peace with Germany. Third, the Allies were determined that in World War II, unlike in World War I, Germany must be comprehensively defeated in the field so that another "stab in the back" myth would not be able to arise in Germany. Operation Valkyrie was intended to be used if the disruption caused by the Allied bombing of German cities caused a breakdown in law and order, or a rising by the millions of slave labourers from occupied countries now being used in German factories. Friedrich Olbricht suggested that it could be subverted to mobilise the Reserve Army to stage a coup. Operation Valkyrie could only be put into effect by General Friedrich Fromm, commander of the Reserve Army, so he had to be won over to the conspiracy or in some way neutralised if the plan was to succeed. Fromm, like many senior officers, knew about the military conspiracies against Hitler but neither supported them nor reported them to the Gestapo. During late 1943 and early 1944 there were a series of attempts to get one of the military conspirators near enough to Hitler for long enough to kill him with a bomb or a revolver. But the task was becoming increasingly difficult. As the war situation deteriorated, Hitler no longer appeared in public and rarely visited Berlin. He spent most of his time at his headquarters in East Prussia, with occasional breaks at his Bavarian mountain retreat in Berchtesgaden. In both places he was heavily guarded and rarely saw people he did not already know and trust. Himmler and the Gestapo were increasingly suspicious of plots against Hitler. On 4 July 1944, Julius Leber, who was trying to establish contact between his own underground SPD network and the KPD's network in the interests of the "united front," was arrested after attending a meeting which had been infiltrated by the Gestapo. There was a sense that time was running out, both on the battlefield, where the eastern front was in full retreat and where the Allies had landed in France on 6 June, and in Germany, where the resistance's room for manoeuvre