Editing Chain Home (section)

===Tizard committee===
The need to research better forms of air defense prompted [[Harry Wimperis]]{{efn|Bowen suggests Tizard was the original impetus for the formation of the Committee and had approached Wimperis to back him up.{{sfn|Bowen|1998|p=4}}}} to press for the formation of a study group to consider new concepts. [[Charles Vane-Tempest-Stewart, 7th Marquess of Londonderry|Lord Londonderry]], then<!--not permanently--> [[Secretary of State for Air]], approved the formation of the [[Committee for the Scientific Survey of Air Defence]] in November 1934, asking [[Henry Tizard]] to chair the group, which thus became better known to history as the [[Tizard Committee]].<ref>{{cite book |first=David |last=Zimmerman |url=https://books.google.com/books?id=k76Q1P4HEmwC&pg=PA23 |title=Top Secret Exchange: The Tizard Mission and the Scientific War |publisher=McGill-Queen's Press |year=1996 |page=23|isbn=9780750912426 }}</ref>

When Wimperis sought an expert in radio to help judge the death-ray concept, he was naturally directed to Watt. He wrote to Watt "on the practicability of proposals of the type colloquially called 'death ray'".{{sfn|Jones|1978|p=19}} The two met on 18 January 1935,{{sfn|Watson|2009|pp=44-45}} and Watt promised to look into the matter. Watt turned to Wilkins for help but wanted to keep the underlying question a secret. He asked Wilkins to calculate what sort of radio energy would be needed to raise the temperature of {{convert|8|imppt}} of water at a distance of {{convert|5|km}} from {{convert|98|to|105|°F}}. To Watt's bemusement, Wilkins immediately surmised this was a question about a death ray. He made a number of [[back-of-the-envelope calculation]]s<ref>{{cite journal |first=B.A. |last=Austin |title=Precursors To Radar – The Watson-Watt Memorandum and the Daventry Experiment |url=http://www.bawdseyradar.org.uk/wp-content/uploads/2012/12/Wilkins-Calculations.pdf |journal=International Journal of Electrical Engineering & Education |volume=36 |year=1999 |issue=4 |pages=365–372 |doi=10.7227/IJEEE.36.4.10 |s2cid=111153288 |url-status=dead |archive-url=https://web.archive.org/web/20150525040134/http://www.bawdseyradar.org.uk/wp-content/uploads/2012/12/Wilkins-Calculations.pdf |archive-date=25 May 2015}}</ref> demonstrating the amount of energy needed would be impossible given the [[state of the art]] in electronics.{{sfn|Watson|2009|p=45}}

According to [[Reginald Victor Jones|R. V. Jones]], when Wilkins reported the negative results, Watt asked, "Well then, if the death ray is not possible, how can we help them?"<ref>{{cite book |first=Reginald Victor |last=Jones |url=https://books.google.com/books?id=hkftkibM5fkC&pg=PT19 |title=Most Secret War |publisher=Penguin |date=2009 |page=19|isbn=9780141957678 }}</ref> Wilkins recalled the earlier report from the GPO, and noted that the [[wingspan]] of a contemporary [[bomber aircraft]], about {{convert|25|m|ft|abbr=on}}, would be just right to form a [[Dipole antenna|half-wavelength dipole antenna]] for signals in the range of 50&nbsp;m wavelength, or about 6&nbsp;MHz. In theory, this would efficiently reflect the signal and could be picked up by a receiver to give an early indication of approaching aircraft.{{sfn|Watson|2009|p=45}}