Coming back to "D" men. My recollection is that on the area side the "D"man was the director and the "A" man his assistant. Titles borrowed from the US where the procedural airways system was originally developed. Of course here in UK the assistant was not a controller grade, although some of us did towards the end of the non radar environment become "A" men. Director has as far as I know always meant an approach radar controller this side of the pond. Incidentally some very good "A" men were actually female, in those far off days gender discrimination was an alien concept.