Stalin. Sensing an opportunity to strike a blow at both the Soviet Army and Admiral Canaris of Germany's Abwehr, Heydrich decided that the Soviet officer should be "unmasked". He discussed the matter with Himmler and both in turn brought it to Hitler's attention. Hitler approved Heydrich's plan to act immediately. But the "information" Heydrich had received was actually misinformation planted by Stalin himself in an attempt to legitimise his planned purges of the Red Army's high command. Stalin ordered one of his best NKVD agents, General Nikolai Skoblin, to pass Heydrich false information suggesting that Marshal Mikhail Tukhachevsky and other Soviet generals were plotting against Stalin. Heydrich's SD forged documents and letters implicating Tukhachevsky and other Red Army commanders. The material was delivered to the NKVD. The Great Purge of the Red Army followed on Stalin's orders. While Heydrich believed they had deluded Stalin into executing or dismissing 35,000 of his officer corps, the importance of Heydrich's part is a matter of conjecture. Soviet military prosecutors did not use SD forged documents against the generals in their secret trial; they instead relied on false confessions extorted or beaten out of the defendants. Night-and-Fog decree By late 1940, German armies had invaded most of Western Europe. The following year, Heydrich's SD was given responsibility for carrying out the Nacht und Nebel (Night-and-Fog) decree. According to the decree, "persons endangering German security" were to be arrested in a maximally discreet way: "under the cover of night and fog". People disappeared without a trace with no one told of their whereabouts or fate. For each prisoner, the SD had to fill in a questionnaire that listed personal information, country of origin, and the details of their crimes against the Reich. This questionnaire was placed in an envelope inscribed with a seal reading "Nacht und Nebel" and submitted to the Reich Security Main Office (RSHA). In the WVHA "Central Inmate File", as in many camp files, these prisoners would be given a special "covert prisoner" code, as opposed to the code for POW, Felon, Jew, Gypsy, etc. The decree remained in effect after Heydrich's death. The exact number of people who vanished under it has never been positively established, but it is estimated to be 7,000. Anti-Polish policies Heydrich created the "Zentralstelle IIP Polen" unit of the Gestapo in order to co-ordinate the ethnic cleansing of Poles in "Operation Tannenberg" and the Intelligenzaktion, two