For most agencies listed here secret policing operations were only part of their function; for instance, the KGB was both the secret police and the intelligence agency.
History of the Soviet state security organs
Detailed chronology
Cheka (abbreviation of Vecheka, itself an acronym for "All-Russian Extraordinary Committee to Combat Counter-Revolution and Sabotage" of the Russian SFSR)
July 10, 1934: NKVD of the Russian SFSR ceases to exist and transforms into the all-union NKVD of the USSR; OGPU becomes GUGB ("Main Directorate for State Security") in the all-union NKVD.
NKVD – "People's Commissariat for Internal Affairs"
May 30, 1947: Official decision with the expressed purpose of "upgrading coordination of different intelligence services and concentrating their efforts on major directions". In the summer of 1948 the military personnel in KI were returned to the Soviet military to reconstitute foreign military intelligence service (GRU). KI sections dealing with the new East Bloc and Soviet émigrés were returned to the MGB in late 1948. In 1951 the KI returned to the MGB.
March 5, 1953: MVD and MGB are merged into the MVD by Lavrentiy Beria.
March 13, 1954: Newly independent force became the KGB, as Beria was purged and the MVD divested itself again of the functions of secret policing. After renamings and tumults, the KGB remained stable until 1991.