Huff-duff allowed operators to determine the location of an enemy radio transmitter in seconds and it became a major part of the network of systems that helped defeat the threat of German U-boats during World War II.

[2][4] Watt led the development of a practical version of this device, which entered service in 1938 under the code name Chain Home.

Watson-Watt had a successful time as a student, winning the Carnelley Prize for Chemistry and a class medal for Ordinary Natural Philosophy in 1910.

[9] He graduated with a BSc in engineering in 1912, and was offered an assistantship by Professor William Peddie,[10] the holder of the Chair of Physics at University College, Dundee from 1907 to 1942.

In 1924 when the War Department gave notice that they wished to reclaim their Aldershot site, he moved to Ditton Park near Slough, Berkshire.

[citation needed] During the First World War, the Germans had used Zeppelins as long-range bombers over Britain and defences had struggled to counter the threat.

Since that time, aircraft capabilities had improved considerably and the prospect of widespread aerial bombardment of civilian areas was causing the government anxiety.

[16] With enemy airfields across the English Channel potentially only 20 minutes' flying-time away, bombers would have dropped their bombs and be returning to base before any intercepting fighters could get to altitude.

[citation needed] Rumours that Nazi Germany had developed a "death ray" that was capable of destroying towns, cities and people using radio waves, were given attention in January 1935 by Harry Wimperis, Director of Scientific Research at the Air Ministry.

[4] Watson-Watt quickly returned a calculation carried out by his young colleague, Arnold Wilkins, showing that such a device was impossible to construct, and fears of a Nazi version soon vanished.

[17] On 12 February 1935, Watson-Watt sent the secret memo of the proposed system to the Air Ministry, Detection and location of aircraft by radio methods.

Although not as exciting as a death-ray, the concept clearly had potential, but the Air Ministry, before giving funding, asked for a demonstration proving that radio waves could be reflected by an aircraft.

[18] This was ready by 26 February and consisted of two receiving antennae located about 6 miles (10 km) away from one of the BBC's shortwave broadcast stations at Daventry.

[19] Such was the secrecy of this test that only three people witnessed it: Watson-Watt, his colleague Arnold Wilkins, and a single member of the committee, A. P. Rowe.

The demonstration was a success: on several occasions, the receiver showed a clear return signal from a Handley Page Heyford bomber flown around the site.

By the end of the year, the range was up to 60 mi (97 km), at which point, plans were made in December to set up five stations covering the approaches to London.

[citation needed] One of these stations was to be located on the coast near Orford Ness, and Bawdsey Manor was selected to become the main centre for all radar research.

Watson-Watt had put another of the staff from the Radio Research Station, Edward Bowen, in charge of developing a radar that could be carried by a fighter.

Night-time visual detection of a bomber was good to about 300 m and the existing Chain Home systems simply did not have the accuracy needed to get the fighters that close.

Bowen decided that an airborne radar should not exceed 90 kg (200 lb) in weight or 8 ft³ (230 L) in volume and should require no more than 500 watts of power.

Watson-Watt justified his choice of a non-optimal frequency for his radar, with his oft-quoted "cult of the imperfect", which he stated as "Give them the third-best to go on with; the second-best comes too late; the best never comes".

[24] In his English History 1914–1945, the historian A. J. P. Taylor paid the highest of praise to Watson-Watt, Sir Henry Tizard and their associates who developed radar, crediting them with being fundamental to victory in the Second World War.

In 1939, Sir George Lee took over the job of DCD and Watson-Watt became Scientific Advisor on Telecommunications (SAT) to the Ministry of Aircraft Production, travelling to the US in 1941 to advise them on the severe inadequacies of their air defence, illustrated by the Pearl Harbor attack.

[2] He wrote an ironic poem ("A Rough Justice") afterwards, Pity Sir Robert Watson-Watt, strange target of this radar plot

The couple lived in London during the winter, and at The Observatory, Trefusis Forbes' summer home, in Pitlochry, Perthshire, during the warmer months.