time was running short. In the winter of 1943, Olbricht declared: "We are ready. The spark can now be set off." Tresckow assured the conspirators that he would take action at the first available opportunity. It came on 13 March 1943, when Hitler finally visited troops on the Eastern Front at Smolensk after a few cancellations and postponements. Under the initial plan, a group of officers were to shoot Hitler collectively at a signal in the officers' mess during lunch but Kluge, commander of Army Group Centre, who had been informed about the plot, urged Tresckow not to carry it out saying, "For heaven's sake, don't do anything today! It's still too soon for that!" He argued that the German army and people were not ready to accept the coup and would not understand such an act. He also feared a civil war between the Army and SS, since Heinrich Himmler had canceled his visit and could not be killed at the same time. Tresckow, however, had a backup plan. During the lunch in question, he asked Lieutenant Colonel Heinz Brandt, who was travelling with Hitler, whether he would be good enough to take a bottle of Cointreau to Colonel Helmuth Stieff (who was not yet a conspirator at that time) at Hitler's headquarters in East Prussia as a payment for a lost bet. Brandt readily agreed. The "Cointreau" was actually a bomb constructed of a British plastic explosive "Plastic C" placed into the casing of a British magnetic mine, with a timer consisting of a spring which would be gradually dissolved by acid. Before Hitler's Condor plane was to take off, Schlabrendorff activated the 30-minute fuse and handed the package to Brandt, who boarded Hitler's plane. After takeoff, a message was sent to the other Berlin conspirators by code that Operation Flash was under way, which they expected to take place around Minsk. Yet when Hitler landed safely at his East Prussian headquarters, it became obvious that the bomb had failed to detonate (the extremely low temperatures in the unheated luggage compartment probably prevented the fuse from working). The message of failure was quickly sent out and Schlabrendorff retrieved the package to prevent discovery of the plot. A week later, on 21 March, Army Group Centre organised a display of Russian Army flags and weapons seized at the Eastern Front. It was exhibited at Zeughaus, military museum in Berlin,