The diary of a WW2 radar technician at Beachy Head refers to an "HD Unit". Can someone pse tell me the meaning of this abbreviation? Thanks in advance. M
From Historical Dictionary of Signals Intelligence by Nigel West, “AI-1(e). At the outbreak of World War II, Air Commodore Lyster Blandy, a Royal Air Force (RAF) officer who retired in 1928 as controller of Air Ministry communications, established an Air Intelligence (AI) intercept facility at RAF Hawkinge in Kent to monitor Luftwaffe voice channels. Designated AI-1(e), his Home Defence Units eventually covered the coastline from Scarborough, Ingoldmells, Gorleston-on-Sea, Capel-le-Ferne, and Beachy Head to Strete and channeled traffic to a disused toy factory at West Kingsdown, Kent.”