sentences:  The worst accident in the history of the unit happened on when Handley Page Halifax "V9977" crashed on 7 June 1942 with the loss all eleven crew and scientists on board including Alan Blumlein.It had been testing the new H2S radar system that used the cavity magnetron valve developed by TRE.In 2002, exactly sixty years later, an RAF Defford Memorial was unveiled by Sir Bernard Lovell on the village green of Defford.