In the 1920s and 1930s, many different designation systems were used for
Russian aircraft; the People's Comissariat of Defence had its own system,
and each manufacturer had another, usually based on the initials of the
designer or organisation (for example, A N Tupolev's ANT-6 was also known
as the TB-3).

Prefixes used included:

    A    = Autogyro
    ARK  = Arctic coastal reconnaissance
    B    = Bomber
    BB   = Short-range bomber
    BSh  = Armoured attack aircraft (Sh = Shturmovik)
    DAR  = Long-range arctic reconnaissance
    DB   = Long-range bomber
    DVB  = Long-range high-altitude bomber
    DI   = Two-seat fighter
    DIS  = Twin-engined escort fighter
    G    = Paratroop transport
    I    = Fighter (Istrebitel; literally "destroyer")
    KOR  = Ship-borne reconnaissance
    M    = Seaplane
    MA   = Amphibian
    MBR  = Short-range maritime reconnaissance
    MDR  = Long-range maritime reconnaissance
    MI   = Fighter seaplane
    MK   = Maritime cruiser (heavily armed seaplane)
    MP   = Transport seaplane
    MR   = Reconnaissance seaplane
    MTB  = Maritime heavy bomber
    MU   = Trainer seaplane
    P    = Mailplane
    PB   = Dive bomber
    PI   = Single seat fighter
    PL   = Transport
    PS   = Mail/passenger transport
    R    = Reconnaissance
    ROM  = Open sea reconnaissance
    SB   = High-speed bomber
    SCh  = Low-level attacker
    SChR = Attack fighter/reconnaissance
    SPB  = Fast dive bomber
    TB   = Heavy bomber
    TSh  = Heavy attack aircraft
    U    = Primary trainer
    UT   = Basic trainer (Uchebnotrenirovochny)
    UTI  = Fighter trainer
    V    = Airship
    VI   = High-altitude fighter
    VIT  = High-altitude tank destroyer
    VT   = Supervised design

In the early years of WW2, a new systematic designation scheme was set up
for all Soviet aircraft (military and civil), based on (usually) the first
two letters of the designer's name; this replaced the former military
designation system.  Later, as the original designers became the heads of
design bureaus (OKBs), and eventually retired or died, the original
initials were retained for all aircraft produced by each OKB.

The full designation consists of the OKB initials, a dash, a number to
indicate a particular aircraft type designed by that OKB, and optionally a
letter or letters (and sometimes numbers) to indicate a subtype.  Unlike
the American system, subtype letters are not a simple alphabetic sequence,
but are assigned arbitrarily, sometimes to indicate some particular feature
of the subtype.  Common suffix letters include "D" (long range), "K" (which
can mean export, ground attack, or naval), "M" (modified), "P"
(interceptor), "R" (reconnaissance), "T" (transport), and "U" (trainer).

Stalin decided that fighters would be given odd numbers, while bombers and
transports would get even numbers; this rule largely fell out of use after
his death.

OKB abbreviations include the following (for those still in use I've added
a description of what the letters look like in the Cyrillic (Russian)
alphabet, since you will often see an aircraft's designation written on
it):

    An  = Antonov          (AH)
    Be  = Beriev           ([broken B] [reversed E])
    Il  = Ilyushin         ([reversed N] [linked JI or inverted V])
    Ka  = Kamov            (KA)
    La  = Lavochkin
    M   = Myasishchyev     (M)
    Mi  = Mil              (M [reversed N])
    MiG = Mikoyan-Gurevich (M [reversed N] [gamma])
    Pe  = Petlyakov
    Po  = Polikarpov
    Su  = Sukhoi           (CY)
    Tu  = Tupolev          (TY)
    Yak = Yakovlev         ([reversed R] K)

The Lavochkin OKB still exists, but switched from aircraft to missile and
space technology in the 1950s.  The Petlyakov and Myasishchyev OKBs are
really the same bureau, which was headed by Myasishchyev after Petlyakov's
death in 1942, disbanded in 1946, but revived in 1952 under Myasishchyev's
name.  Polikarpov's OKB was disbanded after his death in 1944.

The remaining OKBs recently became companies in the wake of perestroika.
With the breakup of the USSR, Antonov is now a Ukrainian company; the rest
are Russian.  Beriev has been renamed Taganrog (after the city in which the
new company is based), and Mikoyan-Gurevich is now just Mikoyan, but the
original abbreviations are retained in their aircraft designations.

One special case is the A-50 AWACS aircraft ("Mainstay").  This was a joint
venture of the Ilyushin and Beriev OKBs (providing the airframe and
electronics, respectively); the A-series designation, normally used by
Beriev to indicate a prototype or experimental aircraft, has been retained
for the production aircraft.  Ilyushin used the designation Il-82 for the
airframe (following the Il-76 transport, Il-78 tanker, and cancelled Il-80
SLAR reconnaissance aircraft, all based on the same airframe); Beriev
argued that they had designed the most important part of the aircraft, so
an Ilyushin designation was inappropriate.  They were still arguing when
the aircraft entered service, so its internal name of A-50 went to the
print shop.

A few cases where confusion has reigned should be mentioned; the present
climate of openness has allowed these to be settled.  All Sukhoi "Flagon"
versions carried Su-15 designations; the later versions were not Su-21
(which in fact referred to Sukhoi's Su-27-derived supersonic bizjet
project, now abandoned).  The designation Tu-20 was used for the early
"Bear" bombers ("Bear-A/B"), but was changed back to Tupolev's internal
designation, Tu-95, from "Bear-C" onwards (some later versions were
Tu-142).  The Tupolev "Backfire" bomber is Tu-22M, not Tu-26.  The
"Fiddler", Tupolev's only production fighter, was Tu-128, not Tu-28.