Following his successful experiment at Tenterden, Maj General Ashmore moved to set up a full - scale trial of Observer Corps’ operations to cover Kent and Sussex . Establishing the method he would later use while expanding the Corps, Gen. Ashmore wrote to the relevant Chief Constables requesting enough volunteer (unpaid) Special Constables to man the 44 Posts (which were incidentally to be between 5 & 8 miles apart.) These Special Constables were to be sworn-in in great secrecy. The Chief Constables in turn talked to Retired Officers , businessmen and landowners, who in turn would ‘persuade’ anyone they thought would be suitable. In this way many Post Observers were estate/land workers and Centre plotters were mainly Bank officials or Local Government Officers or shop staff.
Gen Ashmore then chose the ideal Post locations and requested GPO telephone lines. Each OC Post site was equipped with a telegraph pole connected to the grid, on this pole was a socket into which the ‘field’ telephone was plugged in. There was no cover for the Observers standing beside the telephone pole! The Centre for Maidstone Group was sited in outbuildings of the Telephone Exchange while Horsham’s was in its attic. In charge of these Centres were respectively Police Superintendent J H Day and Police Superintendent H T Knott.
Once the Post crews had been recruited by the Police, Gen Ashmore would interview the Head Special , issue plotting and telephone equipment. He would then run a training session in use of the equipment and make an assessment of the Crew (his reports were quite revealing!).
Both Groups had been set up in time for the RAF Exercises on 22 and 24th June 1925 when the Observer network was thoroughly tested by 3 Squadrons of RAF aircraft flying multiple tracks both day and night. In the ARP Committee Report of 8th July 1925 on the outcome of the Exercises, these were reported as successful and further the recommendation was made that the coverage be extended to cover Hampshire and Essex, thus covering the approach to London from the Continent.
The Committee of Imperial Defence at its Meeting on 29th October 1925 approved the ARP Committee Report and thus the Observer Corps was born with the Terms and Conditions for its future laid down.
The expansion started in 1926 with Winchester (No 3 Group) and Colchester (No 18 Group) using similar methods as for Maidstone and Horsham.
During the period 1927 to,1933 not a single Observer Corps Group was formed, the existing four soldiering on with limited budgets.
The Air Manoeuvres of 1927 were an opportunity to provide a more realistic test for the Corps for the first time since 1918, as these were genuine Air Exercises (as opposed to aircraft supporting ground troops ).
As the speed differential between the fighters and bombers of the day was small, the fighters had to be in the right place at the right time to carry out interceptions and prior to the creation of the Observer Corps the bombers would announce their position to the Fighter Force by wireless!!! The real -time reports of the Observer Corps meant that the fighters now knew where the bombers were. After the 1927 Air Manoeuvres , Air Chief Marshall Sir Robert Brooke-Popham Said the Observer Corps ‘ efforts were “invaluable to the commander of the defending forces”.
In 1928 the work of the Observer Corps was made public with visits to Posts and Centres being allowed but no photographs to be taken of Centres, only Posts.
On 1st January 1929 the control of the Observer Corps was transferred from the War Office to the Air Ministry with Air Commodore G A D Masterman being appointed Commandant. Training was the responsibility of the Air Ministry while recruiting and control of Observers was the remit of the Chief Constables.
The period 1929 – 1930 was one of consolidation, filling gaps in Observer Corps Group coverage, improving the standard of Post plotting, recruiting more Observers for Centres, provision of canvass wind breaks for Posts, and celluloid covers for Post maps. RAF Dispatch Riders were used to transport spare kit to Posts. 1931 saw the Air Ministry impose secrecy surrounding the Corps.
In 1933 the ‘Experimental Grid’ * introduced in the 1924, in which grid positions were duplicated in parts of UK was replaced by the Modified British Grid ** where each grid position was unique.
The year 1934 saw a 6 year expansion programme which resulted in Posts and Centres springing up the length and breadth of Britain, with new officers and thousands of new Observers.
However, those Groups in the expanded Corps that were considered to be beyond the range of enemy bombers were designated as “Back Areas”. Each ‘Back Area’ Post was equipped with a large wooden arow attached to its plotting table in place of a Post Instrument and used simplified reporting procedures.
Until 1939 the Corps held six Exercises annually during June and July between 1800hrs and 1900hrs These were of two types; ‘Communications Exercises’ which were designed to confirm that all telephone connections had been successfully made. ‘Calibration Exercises’ were designed to test the ability of the Corps to carry out its observation and plotting functions satisfactorily. Dummy and sometimes live plots were passed to Centres and RAF personnel would visit Posts and check plots against known flight paths.
