Editing Chain Home (section)

===Detection of aircraft===
In 1931, [[Arnold Frederic Wilkins]] joined Watt's staff in Slough. As the "new boy", he was given a variety of menial tasks to complete. One of these was to select a new [[shortwave]] receiver for ionospheric studies, a task he undertook with great seriousness. After reading everything available on several units, he selected a model from the [[General Post Office]] (GPO) that worked at (for that time) very high frequencies. As part of their tests of this system, in June 1932 the GPO published a report, No. 232 ''Interference by Aeroplanes''. The report recounted the GPO testing team's observation that aircraft flying near the receiver caused the signal to change in intensity, an annoying effect known as [[fading]].{{sfn|Watson|2009|p=44}}

The stage was now set for the development of radar in the UK. Using Wilkins' knowledge that shortwave signals bounced off aircraft, a BBC transmitter to light up the sky as in Appleton's experiment, and Watt's RDF technique to measure angles, a complete radar could be built. While such a system could determine the angle to a target, it could not determine its range and provide a location in space. To do so, two such measurements would have to be made from different locations. Watt's huff-duff technique solved the problem of making rapid measurements, but the issue of coordinating the measurement at two stations remained, as did any inaccuracies in measurement or differences in calibration between the two stations.{{sfn|Clark|1997|p=30}}

The missing technique that made radar practical was the use of pulses to determine range by measuring the time between the transmission of the signal and reception of the reflected signal. This would allow a single station to measure angle and range simultaneously. In 1924, two researchers at the [[Naval Research Laboratory]] in the United States, [[Merle Tuve]] and Gregory Briet, decided to recreate Appleton's experiment using timed pulsed signals instead of the changing wavelengths.{{sfn|Seitz|Einspruch|1998|p=91}} The application of this technique to a detection system was not lost on those working in the field, and such a system was prototyped by [[W. A. S. Butement]] and [[P. E. Pollard]] of the British [[Signals Research and Development Establishment|Signals Experimental Establishment]] (SEE) in 1931. The [[War Office]] proved uninterested in the concept and the development remained little known outside SEE.<ref>{{cite journal |first=R.W. |last=Home |title= Butement, William Alan (1904–1990) |url=http://adb.anu.edu.au/biography/butement-william-alan-12274 |journal=Australian Dictionary of Biography |year=2007}}</ref>