 The Pye strip was such an advance on the EMI unit that the EF50 became a key strategic component . As a German invasion of the west loomed in 1940 , the British contacted Philips and arranged a plan to remove the company 's board of directors to the UK , along with 25 @,@ 000 more EF50s and another 250 @,@ 000 bases , onto which Mullard , Philip 's UK subsidiary , could build complete tubes . A destroyer , HMS Windsor , was dispatched to pick them up in May , and left the Netherlands only days before the German invasion on 15 May 1940 . The Pye strip , and its 45 MHz intermediate frequency , would be re @-@ used in many other wartime radar systems . 
