OSNAZ (Russian: [voiska] osobogo naznacheniya, ОСНАЗ = [войска] особого назначения, "special purpose [detachments]") were special forces troops within the KGB (its predecessors and its successor, Federal Security Service) and the MVD.
OSNAZ has always been shrouded in a veil of mystery and remains so even to this day. There is no OSNAZ headquarters as the various groups were formed within the various directorates as needed.
During the Great Patriotic War the OSNAZ of the NKVD fought on the frontlines against the Nazi Germany as VDV in the form of Airborne regiments/Brigades, with some units achieving "Guards" status at the end of the conflict.
The known KGB OSNAZ units were as follows:
Alpha Group or Spetsgruppa A - formed in 1974 in the Seventh Chief Directorate
Beta Group or Spetsgruppa B - also formed in the Seventh Chief Directorate, time unknown
Vympel or Pennant - formed in August 1981 within the First Chief Directorate as a "sabotage" and covert action unit behind enemy lines. Mission redefined in the late 90s.
Kaskad or Cascade - formed in the 8th Directorate, time unknown
Grom or Thunder - VIP/VVIP Protection Unit
Delfin or Dolphin - a combat diver "incursion" unit similar to the U.S. Navy SEALs.
It is known that several have survived the fall of the Soviet Government and still exist, with the Alpha Group being the most famous.
The Ministry for Internal Affairs (MVD) has several OSNAZ units, such as SOBR. Other MVD units such as Vityaz and "Rus" are classed as Spetsnaz units. They act under the aegis of their corresponding GUVD MVD (Main Internal Affairs Directorate of the Interior Ministry). They are not secret or classified units, even if their operations may be classified.
Caveat: OMON is not an OSNAZ unit. Regular police forces (militsiya) also have their special purpose units (OMSN). MVD OSNAZ units and MVD Interior operative troops (such as ODON operatives) usually wear green or olive berets, the most skilled servicemen being awarded with a purple beret (краповый берет, krapovy beret) after succeeding in a tough competition held every year. The latter OSNAZ members are commonly called krapoviki.
Zaslon is a possible name for a suspected and highly secret OSNAZ organization within the Foreign Intelligence Service (SVR).
OSNAZ is the name for Russian Navy Special Forces. Formed into 1,000 man brigades, one per Fleet. Each brigade consists of several small battalions.