Sector clock
Encyclopedia
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 aircraft and control friendly aircraft.
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.
before modern computerized systems were put in place for airspace control. 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 minute hand at the time of sighting. This data was then reported to sector headquarters such as RAF Bentley Priory
, where counters 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 colour of counter to use for a new sighting was determined by the time of the sighting, the proper colour being indicated by the minute hand of the clock. 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. 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.
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...
mounted on mahogany used at military airfields and observation posts in the United Kingdom to track the movements of enemy aircraft and control friendly aircraft.
History
They were originally known as 'colour change clocks' when introduced by the Royal Flying CorpsRoyal Flying Corps
The Royal Flying Corps was the over-land air arm of the British military during most of the First World War. During the early part of the war, the RFC's responsibilities were centred on support of the British Army, via artillery co-operation and photographic reconnaissance...
in 1917 to monitor the movements of German aircraft. They played a significant role in the Battle of Britain
Battle of Britain
The Battle of Britain is the name given to the World War II air campaign waged by the German Air Force against the United Kingdom during the summer and autumn of 1940...
and continued to be used by the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
and Royal Observer Corps
Royal Observer Corps
The Royal Observer Corps was a civil defence organisation operating in the United Kingdom between 29 October 1925 and 31 December 1995, when the Corps' civilian volunteers were stood down....
until the cold war
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
period and are now sought after by collectors of aeronautica.
Function
The Sector Clock was a fundamental part of Ground-controlled interceptionGround-controlled interception
Ground-controlled interception an air defense tactic whereby one or more radar stations are linked to a command communications centre which guides interceptor aircraft to an airborne target. This tactic was pioneered during World War II by the Royal Air Force with the Luftwaffe to follow closely...
before modern computerized systems were put in place for airspace control. The clock face
Clock face
A clock face is the part of an analog clock that displays the time through the use of a fixed numbered dial or dials and moving hands. In its most basic form, recognized universally throughout the world, the dial is numbered 1–12 indicating the hours in a 12-hour cycle, and a short hour hand...
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 minute hand at the time of sighting. This data was then reported to sector headquarters such as RAF Bentley Priory
RAF Bentley Priory
RAF Bentley Priory was a non-flying Royal Air Force station near Stanmore in the London Borough of Harrow. It was famous as the headquarters of Fighter Command during the Battle of Britain and the Second World War. The RAF Bentley Priory site includes a Grade II* listed Officers' Mess and Italian...
, where counters 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 colour of counter to use for a new sighting was determined by the time of the sighting, the proper colour being indicated by the minute hand of the clock. 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. 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.