Radar Personalities
Wimperis,
Sir Henry Tizard and the Commander-in-Chief of Fighter Command, Air-Vice-Marshal
Sir Hugh Dowding. Far out at sea an "invading" force of flying boats
from Felixstowe turned and headed for Bawdsey. In the stables we, the three
operators, watched our cathode-ray tubes with increasing embarrassment; even
with Lord Swinton breathing down my neck I couldn't see any echoes. By this
time Watson-Watt had switched from promotion to mitigation. Finally even he
stopped talking and in the ensuing deep silence we heard the faint hum of many
distant engines and, at the same moment, saw some weak radar echoes! There was
only just enough time to send a few hastily measured positions to Fighter Command
before the aircraft roared overhead. As a first major demonstration of the use
of radar for air defence it could not have been worse; a good sound locator
would have done better.'
As we soon discovered, the trouble was that the transmitter was not putting out enough power, and when this was put right the performance of the station during the next few days of the Exercise was much better. Nevertheless it was a close shave; the construction of the chain of radar stations might well have been delayed if Watson-Watt hadn't personally persuaded the Chief of the Air Staff to decide, on the basis of the exercise, that 'the RDF system was already proved'. For that we should be profoundly thankful; if the radar chain had not been working in 1940, only four years later, we might well have lost the Battle of Britain.
The filter room
In this first exercise the technique of reporting aircraft positions to Fighter Command was not a success. The original plan was to send them via telephone lines to a device at Fighter Command which showed the position of the aircraft as a bright spot on a map drawn on the face of a cathode-ray tube; but the whole thing, which might have been designed by Heath Robinson, proved so unreliable that it was soon discarded and the results were telephoned. As I have already said, Watson-Watt's aim was to develop a new system of air defence of which the technique of reporting the results to Fighter Command was an integral part, and in 1937 he established a group at Bawdsey to work on this problem. In close collaboration with the RAF this group developed the so-called 'filter room' in which the raw data from several radar stations were correlated and assessed before being passed on to the people whose job was to alert and control the fighters. Coupled with some experiments on controlled interceptions at Biggin Hill, prompted by Tizard, this work led to the remarkably effective operations rooms used by Fighter Command in the Battle of Britain.
This essential system of reporting and filtering the data from the radar chain was ready in time for the Battle of Britain. That was just as well, as is shown by
