The Magnetron - AI at 10 centimetres

A.P. Rowe had shown little interest in Bowen's centimetric work in 1938 at Bawdsey but Sir Charles Wright of the Admiralty was far more encouraging. He asked Bowen what the ideal wavelength should be to remove 'ground clutter' from an airborne signal. Given that the maximum aperture of an aeroplane nose was about 75 cms, Bowen calculated that a 10 cm array would probably fit. Two commercial companies, GEC and EMI were now involved and by June 1940 they had built a 25 cm system with a detection range of 6 miles.

Meanwhile, the "centimeter group" at TRE Worth (to be lead by H.W.B.Skinner and P.I.Dee) was set up. The technical problem at the time was how to produce enough transmitter power for it would be impossible to build equipment that would function at 10 cm wavelengths without at least a 10-fold improvement in power output. A special valve called a Klystron was tried but proved incapable of producing sufficient output...

Then on the 19th July 1940 the first test batch of Magnetrons arrived at Worth and by August the world's first 10 cm echoes were reflected back from the old Norman Chapel on St Aldhelm's Head near Swanage. Two weeks later the 25 cm GEC assembly was converted to run at both 25 cm and at 10 cm…the latter was found to be noticeably superior in performance.