Formation of the Observer Corps
In 1924 the first experiments to assess accurate movements of hostile and friendly aircraft were organised by Major General Ashmore.
Further tests during 1926, proved successful, and plans were made to expand the Observer Groups. During 1929, control of the Observer Corps was transferred to the Air Ministry with the first commandant appointed to the Corps being Air Commodore E.A.D Masterman.
The system of defenses were primarily to protect London. This process relied upon reporting of any aircraft heard or seen within an area of approximately 60 miles of London.
Eventually the system was extended to cover the whole of England and Wales.
The Observation Posts were usually simple constructions generally consisting of emplacements surrounded by sand-bags.
In addition the Observation Posts were issued with an instrument (see photo) which allowed readings to be taken in both direction of movement and aircraft height.
A standardised reporting format based on a common map reporting grid system was established; this allowed readings from two or more posts to be used to provide a more accurate mapping of aircraft position, direction and height.
Training in aircraft types was improved by the issue of aircraft recognition cards