Idflieg Aircraft Designation System

The Idflieg designation system was used to designate German heavier-than-air military aircraft from the early days of the Luftstreitkräfte to the end of World War I. The system necessarily evolved during this period, as new aircraft types were produced. It was never extended to aircraft operated by the German Navy – nor was it applied to lighter-than-air types. Further complicating this situation, German aircraft manufacturers typically used their own designations.

Each designation consisted of one of the following letters, followed by a roman numeral. For example, the first "D"-class aircraft built by Albatros was designated the Albatros D.I, the second, the Albatros D.II and so on.

• A – monoplanes. “A” type aircraft (for example the Rumpler Taube and Fokker M.5) were not limited by any official limiting specification, apart from their wing layout, although they were typically unarmed two seat reconnaissance or training aircraft with low powered engines. After 1915 few “A” types were retained by the Luftstreitkräfte.

• B – biplanes. Again, this designation was not connected to any official specification, apart from the wing layout. In practice, specifications applied to later types limited aircraft retaining the “B” designation after 1915 to low powered unarmed two-seaters, mostly used for training and other second line duties.

• C – two-seat armed biplanes (designation introduced in 1915). This was the first new designation to be introduced after the outbreak of war, and also the first to have a defining specification. In order to reduce the vulnerability of early German military aircraft to Allied types equipped with machine guns, “C” types were armed with a rearward firing machine gun operated by the observer and (later) a forward firing synchronized machine gun for the pilot. An engine of more than 150 hp was also specified (later “C” types typically had over 200 hp). A number of future German fighter aces obtained their first victories in the "C" type
  • CL – lightweight "C" class aircraft (designation introduced early 1917). Later “C” types became progressively larger – the “CL” specification was intended to provide smaller aircraft, nimble enough to be used as a two-seat fighter aircraft. In practice, the “CL” types were mainly used for close support. Engine power of a “CL” was limited to less than 200 hp – and total loaded weight to under 360 kg.. In other respects “CL” types were similar to “C”s – in fact serial and type numbers generally fell in the same sequence.

• D – single-seat armed aircraft, specifically intended for use by the new jagdstaffeln or fighter squadrons (designation introduced in 1916). Until late in 1918, when designations for fighter aircraft were simplified, “D” implied an armed doppeldecker, or biplane. By the end of the war all single seat fighters were designated as “D” types, as distinctions based on wing layout were abandoned.

• Dr – single-seat armed triplane, or Dreidecker (designation introduced in late 1917 – abandoned in late 1918). The first two Fokker Dr.I aircraft were in fact designated “F.I”. By the end of the war the all new single-seat fighters were designated as “D” types, regardless of wing layout.

• E – armed monoplane (designation introduced in 1915 – abandoned in late 1918), from Eindecker. This was initially simply the monoplane version of the “C” class armed biplane, having the same relationship to the “C” class as the “A” had to the “B”, and several early “E” types were two-seaters. In practice, due largely to the success of the single seat Fokker “E” types, which were single seat fighters, the “E” class came to mean a single seat fighter monoplane (i.e. the monoplane equivalent of the “D” class). In late 1918 the last “E” type, the Fokker E.V was redesignated the “D.VIII”, and other late war monoplane types (such as the Junkers CL.I) were also designated in their "functional" class, in line with the abandonment of designations based on wing layout.

• F – single-seat armed triplane (designation used briefly in 1917). Applied only to the Fokker F.I, which was redesignated the “Dr.I” by the time it went into production. As with “A”, “B”, “C”, “D” and “E”, the letter “F” held no intended meaning but was simply the next letter in the original sequence.

• G – armed biplane bomber aircraft with two or three engines (groß - "large") (designation used from 1916). These aircraft were originally designated K (see below).
  • GL – faster twin-engined aircraft suitable for use as a day-bomber or long range reconnaissance (designation introduced in 1918). Bore a similar relationship to the “G” as the “CL” bore to the “C”. Weight and wing span were reduced, and crew was limited to two – the forward gunner’s cockpit being eliminated.

• J – armoured dual-role liaison aircraft and ground attack aircraft (designation introduced in 1917). Most examples resembled “C” types in general layout – differing only in being fitted with armour to reduce vulnerability to ground fire as with the Junkers J.I.

• K – armed biplane bomber aircraft with two or three engines (Kampfflugzeug - "battle aircraft"). Designation introduced in 1915 and replaced by “G” by early 1916.

• N – two-seat single engined night (Nacht) bomber. Basically a “C” type aircraft with longer wing span to enable a heavier war-load. Designation introduced in 1918.

• R – a large bomber aircraft with at least three, in some cases up to six engines (Riesenflugzeug - "giant aircraft"). An important distinguishing feature from the “G” class (apart from size) was that all engines should be accessible in flight to permit running repairs.

• S - seeflugzeuge "seaplane", used as a suffix on other designations as with the Junkers CLS.I and Dornier Rs.IV

The system ceased to apply with the end of German military aviation following the Armistice, and aircraft of the newly reborn Luftwaffe would be designated according to the RLM aircraft designation system although Fokker continued to use a modified form of the system after the war, primarily for C and D class aircraft, while adding or reusing letters for types of aircraft not covered by this system.