to the programme. Also killed in the crash were Blumlein's colleagues Cecil Oswald Browne and Frank Blythen; a TRE scientist Geoffrey S. Hensby, and seven RAF personnel. Magnetron debate As development continued, a great debate broke out in the Air Ministry and RAF about the relative merits of the H2S system. While the ability to bomb in all weather at great distances was obviously useful to Bomber Command, the loss of an H2S aircraft would potentially reveal the secret of the magnetron to the Germans. Churchill's science advisor, Frederick Lindemann, wanted the design team to build H2S around the klystron rather than the magnetron. Unlike a klystron, which is made mostly of glass and fragile metal parts, the magnetron was built out of a single block of copper that would be extremely difficult to destroy with any reasonable demolition charge. If a magnetron was recovered by the Germans, they would immediately understand its operation and potentially develop countermeasures. Since the magnetron was also being designed for use in night fighters and Coastal Command, the loss of the secret would not only provide the Germans with ample early warning to build detectors, but also allow them to develop their own effective airborne radars. The H2S design team did not believe the klystron could do the job, and tests of an H2S built with klystrons showed a drop in output power by a factor of 20 to 30. At the same altitude, the klystron powered versions were able to detect a town at while the magnetron version was capable of . There appeared to be no way to improve this, so it would have to be the magnetron, or nothing. The H2S team also protested that it would take the Germans two years to develop a centimetric radar once the cavity magnetron fell into their hands, and that there was no reason to believe they were not working on the technology already. The first concern would prove correct; although a magnetron was captured in early 1943, the war ended before German examples were in production. In the midst of the debate, Isidor Isaac Rabi of the American Radiation Laboratory visited the TRE offices on 5 and 6 July 1942. According to Lovell, he stated that the H2S device provided to them during the Tizard Mission was "unscientific and unworkable" and expressed his feelings that the only use of it would be to