Aircraft Before WWII Before WWII, aircraft were given designations consisting of a function letter and a sequential number. The basics of the current designation system are very simple. Aircraft are known by the acronym for their design bureau, and a sequential number. The number is odd for fighters and types similar to fighters, and even for other aircraft. The definition of a 'fighter' is rather vague and includes such as the Su-25 'Frogfoot' attack aircraft.
Complication arise because of the way in which subtypes are designated.
Letters are appended to the basic designation, which indicate the type of modification. There is no fixed sequence, and a letter may have another meaning depending on the designation. Bee Hind Gun laying radar for the tail guns of the Tu-95 'Bear'. Big Bulge Radar carried by the 'Bear-D'. Echo Submarine class.