THE SECTOR CLOCK
This is our first ‘dispatch’ from former GCI Radar Station, RAF Ripperston. (and with John in charge, these reports may become a little more frequent than my posts when it was just Jane’s Blog. You have been warned ! Un-follow me now – if you
dare want – the RAF are on our side!) So here we go !
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In the Officer’s Mess at the Set House, there is a sector clock. The Sector Clock was a fundamental part of Ground-Controlled Interception (GCI) during WWII and can be seen in situ in the image of the Reporting Hall, above. The clock face is marked with five-minute red, yellow and blue triangular segments. It has an outer 12-hour ring and an inner 24-hour dial.
Aircraft position was recorded along with the colour of the triangle beneath the minute hand at the time of sighting. This was reported to sector headquarters, where counters of the relayed colour were used to represent each air raid on a large table with a map of the UK overlaid with a British Modified Grid. 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 allowed an estimate to be made of possible targets. The age of the information was readily apparent from the colour of the counter. Because of the simplicity of the system, decisions could be made quickly and easily.
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