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earliest radar devices were designed to provide early warning of the
approach of hostile aircraft, and to this end a chain of stations was
built along the South-east, and East coasts of Britain.
At the outbreak of war in 1939 there were already some eighteen of
these stations in operation, and others quickly followed.
Each station kept constant watch for aircraft flying out to sea and
reported the position of any aircraft that it could see, to Fighter
Command Headquarters. After
the fall of France in June 1940 it became necessary to extend the chain of
stations along the South-west and West coasts and to Northern Ireland, so
that there is now available alrnost complete radar coverage round the
whole country. In
order to appreciate the part played by radar as an early warning device it
is necessary to understand the way in which Fighter Command is organised.
The Headquarters of Fighter Corn-mmd is at Stanrnore in Middlesex.
Directly controlled by this Headquarters are a number of Groups,
each of which is responsible for the defence of a specified region. ,Each
Group has in its area a number of sector stations on which the fighter
aircraft are based. The
movements of fighters at any sector station are under the direction of the
Sector Controller, and he is responsible to the Group Controller, who, in
turn, is responsible to the Chief Controller at Stanmore.
It is necessary for the Controllers at Headquarters and at Groups
and Sectors to have first hand information of the movements of all
aircraft, and particularly of the whereabouts of hostile aircraft, and to
this end an elaborate reporting system has been developed.
It is not possible in this brief account to describe this reporting
system in detail, and only a brief outline of its operation will be given.
Information
concerning aircraft flying overland is supplied by the Royal Observer
Corps and this part of the system does not concern us.
Over the sea, however, aircraft are plotted by the radar stations
round the coast and it is necessary to understand. the way in which this
information is used. Attached
to each Group Station is a Filter Room where information is received from
all radar reporting stations in the Group area.
In the Filter Room is a large scale map of the Group area
which extends for a considerable distance out to sea. This map is mounted on a table around which are seated
W.A.A.F. plotters, each of whom is in constant telephonic communication
with one of the radar stations in the area, and receives information
concerning any aircraft that the station can see.
The operator at the Station passes information to the Filter Room
in the form of plots on the Fighter Command grid, and the plotter who
receives these plots indicates their positions by placing colored counters
on the table. An aircraft
will usually be plotted by more than one Station at one time and it is the
responsibility of an officer, known as a Filterer, to estimate the most
probable position of the aircraft from the plots given by the various
Stations, and to denote this position by placing the arrow on the table.
As the radar stations are capable of measuring the range of a
target with a greater degree of accuracy than the bearing, the Filterer,
whenever two or more stations are plotting an aircraft, assesses its
position by taking range cuts. In charge of the Filter Room is the Filter
officer, and assisting him are liaison officers who maintain contact with
the various branches of the Services and supply information concerning the
positions of our own aircraft and shipping. From the information supplied
by the liaison officers, the Filter Officer is able to identify the tracks
on the Filter Room table. The
filtered plots are read off from the table by Tellers to the Control rooms
of the Sector Stations in the area of the Group in question, to all Group
Control rooms, and to the Central Control Room at Stanmor; where it is
displayed, together with information from the Royal Observer Corps, on
large scale maps. In this way
it is possible to display reliable data before the Controller with the
minimum delay.
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