The meaning of the function letters is listed below. During the war, there were some changes. The most important one is that the letter 'D' was at first only used for biplane fighters, while 'E' was used for monoplane fighters ans 'Dr' for triplane fighters. At the end of the war, the 'D' designation was used for single-seat fighters, even if they were monoplanes. Hence the Fokker E V was renamed Fokker D VIII.
A unarmed reconaissance aircraft B two-seater, with the observer seating in front of the pilot. C two-seater, with the observer in the aft cockpit. CL fast two-seater, multi-role aircraft D 'Doppeldecker', biplane. Later: fighter, in general E 'Eindecker', monoplane. Dr 'Dreidecker', triplane. G 'Grosskampfflugzeug', bomber J ground-attack aircraft K 'Kampfflugzeug', later redisgnated with a G. R 'Riesenflugzeug', long-range bomber.
There was a tendency to use variations of the first digit to related or similar aircraft. For example, Messerschmitt produced a the Bf 110, the Me 210 which was intended to replaced it, the Me 310 design which was an improved Me 210, and the Me 410, which was also an improved Me 210.
Versions were distinguished by capital letters and subdived with numbers, e.g. Ju 88G-6. The number 0 was usually used for pre-series aircraft. Sometimes lowercase letters were added to indicate minor variations, eg. Me 262A-1a. Prototypes had the letter V (for Versuchsflugzeug) and a sequential number, eg. Bf 109 V23.
Aircraft could also be modified with a 'Umbrust' or 'Bausatze' set or be tropicalized; eg. a Bf 109G-2/U1 was a Bf 109G-2 fitted with a reversible pitch prop, an Bf 109G-2/R1 had a 500kg bomb carrier fitted, and an Bf 109E-4/Trop had a dust filter installed.
Bachstelze Wagtail Blitz Lightning Drache Dragon, Kite Falke Falcon Floh Flea Gelber Hund Yellow Dog Greif Griffon Hagelkorn Hailstone Hornisse Hornet Kadett Cadet Kauz Owl Kleinstjager Very small fighter Komet Comet Mistel Mistletoe Natter Viper Pfeil Arrow Stieglitz Goldfinch Storch Stork Stosser Bird of Prey Taifun Typhoon Taube Dove Wal Whale Weihe Kite (bird) Wiking Viking Zwilling Twin