In the 1939 Protection Against Gas & Air Raids - Pamphlet No. 3 Passive Air Defence (Provisional), reference is made to recognition surcoats (these are bibs of material that can be tied at the sides). With various personnel of the Civil Defence and Police wearing top to tail oilskins it would be impossible to differentiate between people and responsibilities. The coloured surcoats was an idea to alleviate this. It was not continued into the wartime period (but a similar use of coloured pennants at Incident Posts does seem to have been initially adopted before being dropped). Helmets were an easier way to differentiate people's roles at incidents.
Green - Rescue
Yellow - Decontamination
Green/White - Wardens' Service
and there were others.
Image courtesy and copyright of Chris Rock.
Passive Air Defence pamphlet courtesy of Adrian Blake.
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