During the build up to World War Two Britain prepared itself for all-out war. Air Raid Precautions were the spearhead of National Civil Defence
When they came the air raids were bad enough but the anticipated scale of attack and mass use of poison gas did not thankfully materialise.
ARP Officers wore white helmets as shown here, with black letters.
Others had white letters on a black helmet, Letters included:-

W for Warden R for Rescue FAP for First Aid Party SP for Stretcher Party A for Ambulance

Photograph above left by Sarony , Ipswich & branches.

Date Stamp on back 28 Mar 1941: Age about 50 years old  • Estimate: born 1893± 7 years