The Battle of Britain Five Months That Changed History, May—October 1940 by James Holland (z-lib.org).epub

for approval to spend development money. Dowding replied that if it could
convince him of its possibilities, he would arrange for the necessary
funding.
On a cold, wintry day in Northamptonshire in February 1935, Watson-
Watt carried out the first of his experiments. A BBC short-wave radio
transmitter, some six miles away in Daventry, provided a continuous radio
beam. The pilot of an RAF Heyford aircraft from Farnborough was told to
fly along a railway line to a point twenty miles away and then back again,
keeping close to the line provided by the beam. He made three runs, and
although on the first he did not fly close enough to the beam, from the
second and third there were clear echoes from the bouncing-back of the
transmission.
Dowding was delighted by the results and immediately authorized the
necessary development money. ‘We now have an embryo,’ Wimperis wrote
to Dowding a week after the experiment, ‘a new and potent means of
detecting the approach of hostile aircraft, one which will be independent of
mist, cloud, fog or nightfall.’
An experimental station was hastily established at Orfordness on the
Suffolk coast. Within six months, Watson-Watt’s Radio Direction Finding –
or RDF, as he called it in an effort to dupe the enemy – was detecting
aircraft at forty miles. It was, however, impossible with one radio mast to
assess the bearing of any incoming aircraft. Only with two or more could a
picture of the position of a plane at any given moment be achieved. Simple
geometry then made it possible to track any oncoming aerial traffic with an
accuracy that improved significantly with experience and as the system was
extended.
Initially five radar stations were ordered to be built. Watson-Watt and
his team moved to Bawdsey, south of Orfordness, in early 1936, by which
time aircraft were being detected as far as sixty-two miles away. All of the
five stations suffered various time-consuming snags; it did not seem
possible to achieve anything with the kind of urgency Dowding required. A
radar training school was set up at Bawdsey in early 1937, and the actual
RDF station there opened in May that year. In July, Dover Chain Home – or
CH – station opened, followed by Canewdon in August in time for
Dowding’s Fighter Command air exercises that same month. Despite
inevitable errors, the results were encouraging. Aircraft were now being
detected at up to a hundred miles away, and immediately afterwards the Air