Squadrons in the 300-series was formed during World War II from those Nationalities that wanted to continue the Fight after thier Countries had be occupied by Germany.
No 400-series Squadrons was formed form Commonwealth Countries Australia, Canada and New Zealand and are shown under thier respective Countries. No 600-series Squadrons was mainly Auxiliary Air Force Units (Royal Auxiliary Air Force from 1947). Higher 600 Numbers was used by Artillery Spotting Squadrons, later transferred to the Army Air Corps.