 This led to what Hanbury Brown describes as " the great minimum range controversy " . From October 1939 , working around the clock to install the remaining Mk . I sets at Perth and St Athan , the team had had no time for further development of the electronics . They were aware that the minimum range was still greater than was satisfactory but Bowen and Hanbury Brown were convinced there was a simple solution they could implement once the initial installations were completed . Meanwhile , the current sets continued to be installed , although all were aware of their problems . On 24 January 1940 Arthur Tedder admitted to Tizard that : 
