Pre-revolutionary Imperial Russia (before 1917) did not have a single national unified system but instead relied on those provided by the manufacturers of the aircraft, like Sikorsky Ilya Muromets or Anatra Anasal.
The Soviet system used from shortly after the revolution in 1923 and until gradually superseded after 1940, was divided by function, with numbers assigned in order by the government.
Not all designations were taken up, some numbers were assigned to projects that were subsequently cancelled, often at a very early stage of development.
Numerical designations were assigned individually for each developer to aircraft when they entered service.
The NATO Air Standardization Coordinating Committee reporting name system (used because designations of new types were often unknown to NATO) was based on an initial letter indicating type of aircraft (B = bomber, C = cargo, F = fighter, H = helicopter, M = miscellaneous) or missile, and 1 syllable if propeller-driven or 2 if jet- or rocket-powered.