The Battle of Britain Five Months That Changed History, May—October 1940 by James Holland (z-lib.org).epub

least his Luftflotten would have built up their strength ready to unleash the
hammer blow.
Air Chief Marshal Dowding was also continuing to make good use of the
respite, for with the rapidly changing situation since 10 May his defensive
system had needed urgent and considerable modifications. This system, so
carefully developed and refined ever since Dowding became C-in-C of
Fighter Command, had become a highly efficient and effective means of coordinating
all his resources to their best capabilities. A key facet was the
radar chain, but this was only one cog in the system. Chain Home and
Chain Home Low were an effective demonstration of the benefit of new
science but it was when they were linked to other cogs that their benefit
really came to the fore.
One of these other cogs was the Royal Observer Corps and its vast
telephone network. Its roots went back to 1917, during the German
Zeppelin and Gotha raids. Major-General Ashmore set up a warning system
for London using various defence units which reported through a new
telephone network to an Operations Room at Ashmore’s headquarters. A
few years after the war, Ashmore refined the system again, using volunteer
civilians to man a series of experimental posts between Tonbridge and
Romney Marsh in Kent. These proved successful, so he was authorized to
set up an observer network that covered all of Kent and Sussex. Dividing
the two counties into a number of zones, each zone was then given a
number of observer posts, each connected by a direct telephone line to an
observer centre, which was in turn linked to Air Defence HQ. Once again,
Ashmore’s system worked well, so the Home Office authorized the
establishment of the Observer Corps, which gradually grew and grew into a
network of ‘Groups’, which were then attached to nearby fighter stations.
Thus No. 1 Group, based in Maidstone, for example, was attached to Biggin
Hill.
By the summer of 1939, there were still gaps in the Observer coverage,
in north-west Scotland, west Wales and Cornwall, but there were now more
than 1,000 posts and some 30,000 observers, all managed by the police.
Observers remained volunteers and trained on evenings and at weekends,
but from 24 August, when the Corps was mobilized, they were expected to
carry out round-the-clock manning of posts. They also came under the
direct control and administration of the Air Ministry. Pay was introduced,