From Sean Waddingham, Golden Green, Kent, UK
Chris Baraniuk, recalling the invention by Russell and Sigurd Varian of the klystron radio amplifier tube, writes that the British won the Battle of Britain thanks in some measure to it (27 May, p 40). But that air battle was fought in daylight, with help from powered by other technology.
British historians from 10 July to 31 October 1940. The first time a klystron-powered Air Intercept radar in a plane enabled the shooting down of an enemy plane , but this technology wasn't crucial in the battle thus defined. Beaufighter night fighters with radar systems (, , rather than klystrons) entered service at the beginning of 1942.
