No mention up-thread of the "Darkie" system that rendered assistance to a myriad of distressed aircraft over the war years and could be considered the precursor of the modern Distress and Diversion Cell. Which system was in use during the timeframe of the subject story, I don't know; but of course Darkie required at least a serviceable receiver. (I do recall - as a Plt Off ATCO - after making some (well deserved, actually!) off-hand and facetious remark to a senior Flt Lt to "get back on the tube and look for aeroplanes flying right-handed triangles!"........)