Operation Valkyrie

Operation Valkyrie (Operation Walküre) was an operational plan developed for the Reserve Army of the German Army (Wehrmacht Heer). The plan was approved by German dictator Adolf Hitler, who intended it to be used in the event that a disruption caused by the Allied bombing of German cities resulted in a breakdown in law and order, or a rising by the millions of forced laborers from occupied countries working in German factories.

German Resistance
In an ironic twist of fate, however, the German Resistance—led by members of the Reserve Army and including members of the Kreisau Circle[1]—modified the plan with the intention of using it to take control of German cities, disarm the SS, and arrest the Nazi leadership once Hitler had been assassinated in the July 20 Plot. Hitler's death was required to free German soldiers from their oath of loyalty to him (Reichswehreid). After lengthy preparation, the plot was carried out in 1944.
Apart from Hitler, only General Friedrich Fromm, commander of the Reserve Army, could put Operation Valkyrie into effect, so he had to be either won over to the conspiracy or in some way neutralized if the plan were to succeed. Fromm, like many senior officers, knew in general about the military conspiracies against Hitler but neither supported them nor reported them to the Gestapo.
The key role was played by German Army (Wehrmacht Heer) officer Claus von Stauffenberg, who was in charge of German Reserve Army's Walküre, a role which allowed him access to Hitler for reports, and required his presence in the coup—which ruled out another suicide attack as planned earlier by other officers. After the first attempt had to be canceled and declared an "exercise", Stauffenberg placed the bomb on July 20 and hurried back to Berlin to assume his pivotal role.
Fromm ordered the executions of General Olbricht, his chief of staff Colonel Albrecht Ritter Mertz von Quirnheim, Colonel von Stauffenberg, and his adjutant Lieutenant Werner von Haeften. Shortly after midnight, the condemned men were led to a mound of earth back lit by idle vehicles where each was executed by firing squad in the courtyard of Bendlerstrasse headquarters. [2]