The Battle of Britain Five Months That Changed History, May—October 1940 by James Holland (z-lib.org).epub

Note on the Text
So as not to cause any confusion, I have used German ranks, rather than
English translations. I have also called German units by their German
names, largely because when writing about something from the German
perspective, it seemed odd not to do so. Thus I have called German motor
torpedo boats S-boats – as in Schnellboote – rather than E-boats, as the
British termed them.
Equally, I have referred to German air units in the German terminology,
partly to help distinguish them from British units, but also because their
units were not quite the same as those in the RAF. The largest Luftwaffe
force was the air fleet, or Luftflotte, and within each Luftflotte were
Fliegerkorps (air corps). Beneath that there could even be
Fliegerdivisionen. However, the principal air unit was the Geschwader,
which contained three Gruppen; each Gruppe then had three Staffeln. Thus
2/JG 2 was the second Staffel of the first group of Jagdgeschwader 2. A
Jagdgeschwader was a fighter unit, a Kampfgeschwader a bomber unit.
Staffeln were always labelled with Arabic numbers, Gruppen by Roman
numerals. Thus III/KG 4, for example, was the third Gruppe of
Kampfgeschwader 4. A fighter Staffel would have a theoretical
establishment of twelve aircraft, but usually an operational number of nine.
A bomber Staffel would have a theoretical establishment of nine, and an
operational number of one or two less.
The RAF did not have an organization based on army structure, but
rather was separated into commands, which from Britain were divided into
Fighter, Bomber, and Coastal Commands. The principal unit within these
commands was the squadron. Fighter squadrons had a theoretical
establishment (IE or immediate establishment) of sixteen aircraft, of which
at least twelve would be operational. They also had an IE of twenty pilots.