which Hitler was to visit on Heroes' Memorial Day with Himmler and Hermann Göring. Colonel Gersdorff volunteered to be the suicide bomber, intending to explode a bomb on his person near Hitler while serving as a tour guide. He had with him bombs with ten-minute fuses, knowing that Hitler was scheduled to be in the museum for 30 minutes. But at the last minute, just before Hitler was to arrive, the duration of his stay was reduced to just eight minutes as a security precaution. Hitler breezed through in two minutes. As a result, Gersdorff could not accomplish his mission, the assassination plan failed again and he barely managed to get out and defuse the bombs. Other plots similarly failed because of Hitler's irregular habits. Most importantly, they had no access to Hitler since he no longer visited the front, rarely visited Berlin and spent most of his time at the Wolf's Lair in East Prussia or the Berghof in Bavaria. Tresckow lacked the required clearance to enter either site and the extremely high security made any attempt impractical and unlikely to succeed. The elimination of Oster's group in April 1943 (his deputy Hans von Dohnanyi and Lutheran theologian Dietrich Bonhoeffer were arrested, and Oster was placed under house arrest) was a further setback. Tresckow worked tirelessly to persuade army commanders such as Field Marshals Fedor von Bock, Günther von Kluge and Erich von Manstein to join in the conspiracy without much success. With unwitting help from Schmundt, he placed like-minded officers as their adjutants and staff officers to bring them closer to the conspiracy. Kluge sympathised with the conspirators and at times seemed ready to act, only to become indecisive at critical moments. Others refused outright, Manstein declaring, "Prussian field marshals do not mutiny." Nonetheless, no-one reported their treasonable activities to the SS. Operation Valkyrie Eventually, the conspirators came to rely more on the Reserve Army in Berlin and other districts to stage a coup against the German government. Olbricht now put forward a new strategy for staging a coup against Hitler. The Reserve Army had an operational plan called Operation Walküre (Valkyrie), which was to be used in the event that the disruption caused by the Allied bombing of German cities caused a breakdown in law and order, or an uprising by the millions of slave laborers from occupied countries now being used in German factories. Olbricht suggested