Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Polish operation of the NKVD refers to the coordinated actions of the NKVD in 1937-1938, done according to NKVD Order 00485 " - " ("On the liquidation of the Polish diversionist and espionage groups and POW units"). The order was approved on August 9, 1937 by the VKP(b) Central Committee Politburo, and was signed by Nikolai Yezhov on August 11, 1937. It was distributed to the local subdivisions of the NKVD simultaneously with Yezhov''s secret letter, " - , , , " ("On fascist-resurrectionist, spying, diversional, defeationist, and terrorist activity of Polish intelligence in the USSR"). The operation was the second in a series of national operations of the NKVD, justified by the Soviet government by the fear of a fifth column (in the expectation of war with "the most probable adversary", that is, Germany), and by thenotion of a "hostile capitalist surrounding", bent on destabilizing the Soviet Union.