The Sector Clocks used in operations rooms during the Battle of Britain were known as ‘colour change clocks’ during the First World War when they were introduced by the Royal Flying Corps in 1917 to assist in the monitoring of the movements of German aircraft. During the Battle of Britain, the clock was a fundamental part of ground-controlled interception with the clock face marked with five-minute red, yellow and blue triangular segments and had an outer 12 hour ring and an inner 24 hour dial.
Aircraft positions were recorded along with the colour of the triangle beneath the minute hand at the time of sighting. These were reported to Fighter Command Group and Sector Operations Rooms, where pointers of the relayed colour were used to show the progress of each air raid plot 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 and pointers were pushed across the map by plotters (usually WAAFs) using magnetic “rakes”. This system enabled Group and Sector 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 pointer and a ‘lost’ plot could be easily identified. Because of the simplicity of the system, decisions could be made quickly and easily.
AN EXAMPLE OF A SECTOR CLOCK IS DISPLAYED IN THE MUSEUM’S RECEPTION AREA