Walter Krivitzky, the the high-ranking Main Intelligence Administration (GRU) officer who defected and wrote In Stalin's Secret Service (New York: Holt, 1939) told Whittaker Chambers that the Soviet Union practiced a form of fascism, and this became manifest in 1921 when Lenin ordered the suppression of the Kronstadt mutiny, turning against the very sailors whose 1917 mutiny propelled the Bolsheviks to power.
The Bolshevik "Night of the Long Knives".