Hi, Simon...
In additional to Christian's information, it might be of interest to you to know that the first two characters in the pre-war codes indicated the
Luftkreis (air dristrict) and numerical position of the unit within that
Luftkreis. '35' therefore, would indicate Luftkreis 3 (Headquarters at Dresden), and St.G.163 being the fifth Geschwader within that area. '52' indicated Luftkreis 5 with its Headquarters at Munich, and St.G.165 being the second Geschwader of that area.
Regards...
