When did the campaign of political  repression that Mikhail Demichev was arrested during occur?
Mikhail Demichev Mikhail Demichev (1885 – November 19, 1937) was a Soviet Komdiv (division commander). He fought in the Imperial Russian Army in World War I before going over to the Bolsheviks in the subsequent civil war. He was a recipient of the Order of the Red Banner. During the Great Purge, he was arrested on August 9, 1937 and later executed. After the death of Joseph Stalin, he was rehabilitated in 1956.
Polish Operation of the NKVD The Polish Operation of the Soviet NKVD security service in 1937–1938 was a mass operation of the NKVD carried out against purported Polish agents in the Soviet Union during the period of the Great Purge. It was ordered by the Politburo against the so-called "Polish spies" and customarily interpreted by the NKVD officials as relating to "absolutely all Poles". It resulted in the sentencing of 139,835 people, and summary executions of 111,091 ethnic Poles, as well as those accused of working for Poland. The operation was implemented according to NKVD Order № 00485 signed by Nikolai Yezhov. The majority of the victims were ethnically Polish but not all, according to Timothy Snyder. The remainder were 'suspected' of being Polish, without further inquiry. In order to speed up the process the NKVD personnel reviewed local telephone books and arrested persons with Polish-sounding names.