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The original Operation Valkyrie plan was developed in December 1941.
Unternehmen Walküre (translated)
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Soldiers of the reserve army were supposed to occupy important points in Berlin and other larger cities and take action against insurgents. The activation by the code word 'Valkyrie' was reserved for Adolf Hitler personally and for the commander of the replacement army.
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This plan needed adaptations that gave the army a more central role in the operation. These adaptations needed authorization, that was given by Hitler in 1943.
This is the scene shown in the movie.
What are the primary reasons they would go to such lengths to acquire a real signature, instead of forging it?
To have made the needed changes without authorization would have swiftly led to an investigation as to the reason why, which the planners wished to avoid.
Although not all portions of the film was considered historically correct, the plot itself and the events at the Bendlerblock are as near as you can get for a Holywood film.
Peter Hoffmann, who is a Stauffenberg biographer, was their 'informal' historical advisor.
Wem gehört der 20. Juli 1944?
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Der „Bild“-Zeitung zählte Knopp dann kurze Zeit später jene fünf „Fehler“ auf, die er in Bryan Singers Film gefunden hatte. Ähnlich tat dies auch Peter Steinbach, der wissenschaftliche Leiter der Gedenkstätte Deutscher Widerstand in Berlin.[7] Nur Peter Hoffmann, der als „informeller Berater“ am Film mitgewirkt hatte, sah Bryan Singers Werk wirklich als gelungen an.
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[7] Peter Steinbach, Historiker Steinbach: Die unsägliche Fehler im Film „Operation Walküre“, in Hamburger Abendblatt, 22.1.2009.
[8] Jordan Mejias, Wir wollen der Welt vom 20. Juli erzählen, in: FAZ.net, 23. Januar 2009.A short time later, Knopp listed the five “mistakes” that he had found in Bryan Singer's film for the “Bild” newspaper. Peter Steinbach, the scientific director of the German Resistance Memorial Center in Berlin, did a similar job. [7] Only Peter Hoffmann, who had worked as an “informal advisor” on the film, really saw Bryan Singer's work as successful.
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