 During the Second World War he worked in the Radiophysics Laboratory in Sydney , where he produced a laboratory model of a cavity magnetron . In September 1942 , he returned to Melbourne as the officer in charge of the Radar Research Laboratory , where he continued the development of cavity magnetrons and reflex klystrons for radar sets . In May 1944 , he became one of three Australian physicists who worked on the Manhattan Project , which created the first atomic bombs . 
