Sector clock

A Sector clock was a round clock mounted on mahogany used at military airfields and observation posts in the United Kingdom to track the movements of enemy aircaft and control friendly aircraft.

History

They were originally known as 'colour change clocks' when introduced by the Royal Flying Corps in 1917 to monitor the movements of German aircraft. They played a significant role in the Battle of Britain and continued to be used by the Royal Air Force and Royal Observer Corps until the cold war period and are now sought after by collectors of aeronautica.

Function

The clock face had a 12 hour dial and an inner ring for the 24 hour time widely used by the military and was marked with red, blue and yellow triangular segments. The position of the sighted aircraft was recorded, together with the colour of the triangle beneath the second hand at the time of sighting. This data was then reported to sector headquarters such as Bentley Priory, where counters of corresponding colours representing each air raid were placed on a large table, which had a map of the UK overlaid and squared off with a British Modified Grid. The red, yellow and blue colour coding of each counter was changed every five minutes. As the plots of the raiding aircraft moved, the counters were pushed across the map by magnetic "rakes". This system enabled "Fighter Controllers" to see very quickly where each formation was heading and allowing an estimate to be made of possible targets. Because of the simplicity of the system decisions could be made quickly and easily.

External Links

* [http://home.earthlink.net/~modguide/opsroom.html 'The clock that saved Great Britain']
* [http://www.ww2-pathfinders.co.uk/Wyton%20sector%20clock.html RAF Wyton Sector Clock]