Sir Robert Watson-Watt and Atmospheric Radio Science

The Atmosphere in 1915

When Watson-Watt began his career, the radio age was barely a decade old, and it had already produced a genuine scientific mystery. On 12 December 1901, Guglielmo Marconi sent a wireless signal across the Atlantic, from Poldhu in Cornwall to St John's in Newfoundland — a result that, by the physics then understood, should have been impossible. Radio waves were thought to travel in straight lines, while the curve of the Earth should have carried the receiving station out of a direct line of sight long before the signal could arrive. Something, evidently, was bending or reflecting the waves back down to Earth.

In 1902, two men on opposite sides of the Atlantic independently proposed the same solution. The American electrical engineer Arthur Edwin Kennelly and the British physicist Oliver Heaviside each suggested that a high, electrically conducting layer of the atmosphere was acting as a mirror, bouncing radio waves back toward the ground. This hypothetical reflecting layer became known as the "Kennelly–Heaviside layer." For more than two decades it remained an unproven hypothesis; many working engineers were openly sceptical that it existed at all. Definitive experimental proof would not arrive until 1924, when Edward Appleton and Miles Barnett measured its height directly — work for which Appleton alone received the 1947 Nobel Prize in Physics.

Lightning presented an even murkier puzzle. Anyone who owned a wireless set knew that thunderstorms produced bursts of crackling interference, nicknamed "atmospherics" or "sferics" by radio operators. But precisely how lightning generated these radio bursts, and whether the phenomenon could be turned to practical use, was poorly understood. This was the specific scientific problem the Meteorological Office handed to the young Watson-Watt in 1915: find a way to detect and locate thunderstorms from their radio emissions, so that meteorologists could warn aviators — flying fragile, fabric-and-wire aircraft — of dangerous weather lying beyond the horizon. It amounted, in effect, to the world's first serious attempt at radio-based weather surveillance.

Locating Thunderstorms

Watson-Watt's basic insight was simple to state and difficult to achieve: every lightning discharge radiates a broadband burst of radio energy that can travel hundreds, even thousands, of miles. If the direction from which such a burst arrived could be measured accurately, a line could be drawn straight toward the storm; combine bearings from two or more separated stations, and the storm's position could be fixed precisely by triangulation.

He began this work at the Wireless Station of the Air Ministry Meteorological Office at Aldershot, in a wooden hut where his first wife, Margaret — sometimes called "the mother of radar" — helped solder his apparatus and record observations. The first problem was directional: he used antennas that could be rotated to maximise or minimise a signal, "pointing" toward the storm. The second, much harder problem was speed. A lightning sferic lasts only a tiny fraction of a second — far too fleeting for a swinging needle or a mechanical pen recorder to capture reliably. Watson-Watt's answer, proposed in 1916, was to feed the signal into a cathode-ray oscillograph, so that a single flash would instantly paint a line of light on the screen showing its bearing. The idea was years ahead of the available hardware: reliable cathode-ray tubes only became available around 1923, after which the method finally came into its own.

His earliest scientific publications grew directly out of this work. He produced "Directional Observations of Atmospherics, 1916–1920" (Philosophical Magazine, series 6, volume 45, pages 1010–1026, 1923), and in 1922 published the short note "The Origin of Atmospherics" in Nature(volume 110, pages 680–681), reporting that "actual thunderstorms could be located by direction-finding on atmospherics" in a Meteorological Office investigation begun in 1915. He also co-authored "The Study of Radiotelegraphic Atmospherics in Relation to Meteorology" with C.J.P. Cave, published in the Quarterly Journal of the Royal Meteorological Society in 1923.

In 1924, when the War Department reclaimed the Aldershot site, Watson-Watt moved his work to Ditton Park, near Slough, where the National Physical Laboratory already had a presence. There he gained access to two decisive pieces of equipment: an Adcock antenna — an array of four masts that sensed a signal's direction from phase differences between them — and a modern oscilloscope acquired from Bell Labs. By feeding the outputs of crossed Adcock antennas into the X and Y channels of the oscilloscope, a single lightning stroke produced a line on the screen pointing directly at the storm. This became known as Cathode Ray Direction Finding, or CRDF, and radio engineers still refer to the underlying method as the "Watson-Watt" or "Adcock/Watson-Watt" technique. In 1926, with J.F. Herd, he published "An instantaneous direct-reading radiogoniometer" in the Journal of the Institution of Electrical Engineers (volume 64, pages 611–622), describing the direction-finding instrument at the heart of the whole system.

In 1927 the Meteorological Office's and the National Physical Laboratory's radio research teams were formally amalgamated into the Radio Research Station, operating under the Department of Scientific and Industrial Research, with Watson-Watt appointed superintendent. He became head of the radio department of the National Physical Laboratory at Teddington in 1933. By the early 1930s, the station could locate storms by direction-finding from multiple receivers and correlate them with the movement of cold-air weather fronts — a genuinely remarkable feat of practical atmospheric science for its time. In 1929 he summarised the field for a wider scientific audience in the G.J. Symons Memorial Lecture, "Weather and Wireless," published in the Quarterly Journal of the Royal Meteorological Society (volume 55, pages 273–301, delivered 20 March 1929).

Sounding the Ionosphere

The same basic toolkit that located thunderstorms could also be turned upward, to probe the sky itself. The ionosphere — a term Watson-Watt himself coined — is the electrically charged upper region of the atmosphere, ionised by the Sun's ultraviolet and X-ray radiation knocking electrons off atmospheric gases, beginning at roughly 60 to 100 kilometres altitude. It is precisely the layer Kennelly and Heaviside had hypothesised more than two decades earlier.

Edward Appleton initially measured the layer's height using a frequency-variation method: the 1924 Appleton–Barnett experiment, using a BBC transmitter at Bournemouth, established a reflecting layer at about 100 km, providing the first firm experimental confirmation that the Kennelly–Heaviside layer genuinely existed. Watson-Watt's group at Slough pursued a different, complementary approach — the pulse method — sending a sharp radio pulse upward and timing precisely how long its echo took to return, exactly as a radar set would later time the echo from an aircraft. To make this possible, the team needed a way to sweep the spot on a cathode-ray tube smoothly across the screen at a very high, precisely known speed, so that the echo's delay could be read directly off the display as a height. Working with E.V. Appleton and J.F. Herd, Watson-Watt developed the "squegger" — a self-oscillating time-base circuit — to provide exactly that linear sweep. The work appeared in the joint paper "On the Nature of Atmospherics," published by Appleton, Watson-Watt and Herd in Proceedings of the Royal Society A, volume 111, in 1926. This time-base technology is a direct technical ancestor of the radar display.

It was in a letter dated 8 November 1926, addressed to the secretary of the Radio Research Board, that Watson-Watt proposed the word "ionosphere," reasoning that it deserved a place alongside the newly adopted terms "stratosphere" and "troposphere." The word did not actually appear in print until 1969, but it came into general scientific use during the early 1930s. In 1924 he had also noted an apparent enhancement of the ionosphere during local thunderstorms — an intriguing observation that, remarkably, was not properly followed up until researchers at Reading University revisited it in 2005.

The Scientific Method

The elegance of Watson-Watt's overall approach can be set out in a few plain steps, and it is worth doing so explicitly, because the same steps reappear, essentially unchanged, in radar a decade later.

• A lightning flash is a natural radio transmitter. Each discharge radiates a broadband "sferic" that races through the gap between the ground and the ionosphere and can be detected thousands of kilometres away.
• A directional antenna finds the bearing. Rotating an antenna, or using crossed fixed antennas, reveals the direction of strongest or weakest signal — a line pointing toward the storm.
• Two stations triangulate. Crossing the bearings from two or more separated stations locates the storm's position where the lines intersect.
• The cathode-ray tube reads it in an instant. Because a sferic lasts only milliseconds, the cathode-ray display captures the bearing of each individual flash as a streak of light, fast enough to track a live, moving storm.
• For the ionosphere, send a pulse and time the echo. A radio pulse fired straight up bounces off the ionosphere; the time delay, read off the calibrated cathode-ray time base, gives the layer's height.

Every one of these techniques — directional finding, triangulation, the cathode-ray display, and pulse-echo ranging — is a direct intellectual ancestor of radar. Radar simply turns the same set of ideas on a new kind of target: instead of waiting for lightning to transmit on its own, the radar set provides its own outgoing pulse, and instead of reading an echo from the ionosphere, it reads an echo bounced back from an aircraft.

The Bridge to Radar

By the mid-1930s, Watson-Watt had spent twenty years doing precisely the things radar would require: detecting faint, fleeting radio signals; building sensitive receivers and directional antenna systems; displaying direction and timing information on cathode-ray tubes; and timing radio echoes from distant reflectors to measure range. When, in early 1935, the Air Ministry's H.E. Wimperis asked him whether radio could be used to build a "death ray" capable of disabling enemy pilots, Watson-Watt set his assistant Arnold Wilkins to calculate the energy such a device would require, found the result hopelessly impractical, but — drawing directly on his life's atmospheric research — pointed instead to "the still difficult but less unpromising problem of radio detection."

His memorandum, "Detection and Location of Aircraft by Radio Methods," reached the Air Ministry on 12 February 1935. The relevant committee asked for proof. On 26 February 1935, near Daventry, Watson-Watt, Wilkins and a single witness from the Tizard Committee, A.P. Rowe, used a BBC shortwave transmitter and two receiving antennas to detect a Handley Page Heyford bomber; according to the National Library of Scotland, the aircraft was detected at a range of about 13 miles, a distance later extended to some 75 miles with a more powerful transmitter. The reflected signal deflected the trace on a cathode-ray tube — in essence, his thunderstorm-and-ionosphere apparatus, pointed at an aeroplane instead of the sky. The two decades of atmospheric science had made the man ready; the invention that followed is a fuller story, told in our companion Inventions Collection article on radar.

Legacy: From Sferics to Satellites

Watson-Watt's atmospheric radio science is not a historical footnote; it remains alive today. The direction-finding of sferics he pioneered in the 1920s and 1930s evolved into the UK Met Office's Arrival Time Difference network, ATDnet, a VLF system the Met Office has run since 1987 that locates lightning to within 1–3 km with greater than 90% cloud-to-ground detection efficiency across the UK and Western Europe. Its 2025 successor, LEELA (Lightning Electromagnetic Emission Location by Arrival time difference), uses a network of eleven sensors distributed around Europe.

Globally, the World Wide Lightning Location Network (WWLLN), operated jointly by the University of Washington in Seattle and the University of Otago in New Zealand, began in 2004 with 18 stations and has since grown to around 70 active VLF receiving stations, detecting sferics in the 6–22 kHz band at ranges up to 10,000 km — the very class of signals Watson-Watt first learned to read systematically a century earlier. The study of sferics is an active research field today, now linked to phenomena such as "sprites" and the global atmospheric electric circuit. The ionosphere, too, remains scientifically vital: it bends and delays GPS satellite signals, so understanding its behaviour matters directly for modern satellite navigation, and continuous ionospheric measurement begun in this era continues worldwide.

For his scientific contributions, Watson-Watt was elected a Fellow of the Royal Society in 1941 — and, tellingly, his citation praised him "for his contributions to meteorological physics, as elucidated by radio methods" and his pioneering use of the cathode-ray oscillograph, wording chosen partly to avoid revealing the still-secret existence of radar. He was knighted in 1942, received the US Medal for Merit in 1946, the Royal Society's Hughes Medal in 1948, and served as President of the Royal Meteorological Society. His major technical legacy publications include the 1933 monograph "Applications of the Cathode Ray Oscillograph in Radio Research," written with J.F. Herd and L.H. Bainbridge-Bell and published by HMSO for the DSIR, and his 1957 autobiography, Three Steps to Victory.

Character and Later Life

Watson-Watt was a prolific, practical, entrepreneurial — and sometimes controversial — figure. He described himself as a "plausible salesman of ideas," a self-publicist who relished attention, and a man of considerable Scottish pride. His most famous working principle was the "cult of the imperfect": "Give them the third best to go on with; the second best comes too late, the best never comes." It was exactly this willingness to deploy a good-enough system rather than wait for perfection that helped put a working radar chain around Britain in time for 1940.

His private life was tangled: he married three times — first to Margaret Robertson in 1916 (divorced 1952), then to the Canadian Jean Drew Smith in 1952 (she died in 1964), and finally, in 1966, to Dame Katherine Trefusis Forbes, founding director of the Women's Auxiliary Air Force, which had supplied the radar-room operators during the war. In 1952 the Royal Commission on Awards to Inventors granted him a tax-free £50,000 "in respect of his initiation of radar and his contribution to the development of radar installations" — the top individual prize from a total of £94,600 the Commission granted to 24 scientists that year, and the highest single payment the Royal Commission ever made. Some contemporaries felt the recognition still fell short of what radar had achieved for Britain.

One of the more delightful stories about him dates to 1956: living in Canada by then, the elderly Watson-Watt was pulled over for speeding by a policeman using a radar speed-gun and was, in the words of Scotland's People, "fined $12.50 on the spot." He is reported to have exclaimed, "Had I known what you were going to do with it I would never have invented it!" — and afterward wrote a wry poem, "Rough Justice," which begins: "Pity Sir Robert Watson-Watt, / strange target of this radar plot / and thus, with others I can mention, / the victim of his own invention." He died on 5 December 1973 in Inverness and is buried at Pitlochry; in 2014 the Princess Royal unveiled a statue of him in his native Brechin.

Timeline

1. 1892

   Robert Alexander Watson-Watt born, 13 April, Brechin, Angus

   Fifth son and youngest child of carpenter and cabinet-maker Patrick Watt

2. 1901

   Marconi transmits a wireless signal across the Atlantic

   A result that should have been impossible given the curvature of the Earth, prompting the Kennelly–Heaviside hypothesis

3. 1902

   Kennelly and Heaviside independently propose a conducting atmospheric layer

   The hypothetical 'Kennelly–Heaviside layer' that reflects radio waves back to Earth

4. 1912

   Watson-Watt graduates BSc in engineering, University College, Dundee

   Professor William Peddie steers him toward wireless telegraphy and radio physics

5. 1915

   Joins the Meteorological Office to locate thunderstorms by radio

   The founding problem of his career: warning aviators of storms beyond the horizon

6. 1916

   Proposes using a cathode-ray oscillograph to display a lightning bearing instantly

   The idea preceded reliable hardware by roughly seven years

7. 1922

   Publishes 'The Origin of Atmospherics' in Nature

   Reports that thunderstorms could be located by direction-finding on atmospherics

8. 1923

   Reliable cathode-ray tubes become available; publishes 'Directional Observations of Atmospherics, 1916–1920'

   The CRT direction-finding method finally comes into its own

9. 1924

   Moves to Ditton Park, near Slough, after the War Department reclaims Aldershot

   Gains access to Adcock antennas and a modern oscilloscope from Bell Labs

10. 1924

    Appleton and Barnett measure the height of the ionosphere directly

    First definitive experimental proof of the Kennelly–Heaviside layer, using a BBC transmitter at Bournemouth

11. 1926

    Develops the 'squegger' time-base circuit with Appleton and Herd

    Enables precise timing of radio echoes from the upper atmosphere — a direct ancestor of the radar display

12. 1926

    Coins the term 'ionosphere' in a letter dated 8 November to the Radio Research Board

    Reasoned it deserved a place alongside 'stratosphere' and 'troposphere'

13. 1927

    Meteorological Office and NPL radio teams merge into the Radio Research Station

    Watson-Watt becomes superintendent, at Ditton Park under the DSIR

14. 1929

    Delivers the G.J. Symons Memorial Lecture, 'Weather and Wireless'

    Distills two decades of atmospheric radio research for a wider scientific audience

15. 1933

    Becomes head of the radio department of the National Physical Laboratory, Teddington

    Publishes 'Applications of the Cathode Ray Oscillograph in Radio Research' with Herd and Bainbridge-Bell

16. 1935

    12 February memorandum and 26 February Daventry experiment

    Two decades of atmospheric radio science are redirected toward detecting aircraft

17. 1941

    Elected Fellow of the Royal Society

    Citation praises his contributions to meteorological physics via radio methods and his pioneering use of the cathode-ray oscillograph

18. 1942

    Knighted

    Recognition following the acknowledged success of the radar chain in the Battle of Britain

19. 1973

    Dies, 5 December, Inverness; buried at Pitlochry

    A statue was unveiled in his native Brechin by the Princess Royal in 2014

Myths & Facts

Did You Know?

• Watson-Watt spent twenty years using radio to study thunderstorms and the ionosphere before radar — the atmospheric work was both the foundation and the apprenticeship.
• He used a cathode-ray tube to display the direction of thunderstorms years before anyone thought to use the same idea to show aircraft positions.
• He coined the word 'ionosphere' — in a letter dated 8 November 1926 to the Radio Research Board.
• His work made aviation safer long before radar existed, by letting weather forecasters warn pilots of distant storms.
• The Met Office's modern lightning-warning network (ATDnet and its successor LEELA) and global sferics networks like WWLLN descend directly from the techniques he pioneered.
• In 1956 he was caught in a radar speed trap in Canada, fined $12.50, and quipped that, had he known, 'I would never have invented it!'

Honest Caveats

Watson-Watt did not discover the ionosphere. Its existence was hypothesised by Kennelly and Heaviside in 1902, and its height was first proved experimentally by Edward Appleton and Miles Barnett in 1924, work for which Appleton alone received the 1947 Nobel Prize in Physics. Watson-Watt's distinct contribution was the pulse-echo timing method and, notably, coining the term "ionosphere" itself.

"Inventor of radar" is a simplification that belongs to a separate article. Many nations and earlier figures — including Heinrich Hertz and Christian Hülsmeyer — contributed to the broader story of radio detection, and Watson-Watt himself credited close colleagues. This article deliberately confines itself to his atmospheric science and treats radar only as its destination.

Some dates differ slightly between sources. A few accounts give his Meteorological Office start as 1916 rather than 1915; some sources emphasise the 1924 move to Slough, others the 1927 administrative merger into the Radio Research Station — both events are correct and simply refer to different milestones.

His earliest "lightning" publication date is sometimes conflated. One history dates a paper on lightning-generated radio waves to 1922 (the Nature note "The Origin of Atmospherics"), while his major early research paper, "Directional Observations of Atmospherics, 1916–1920," is dated 1923. Both are genuine and distinct publications.

The Daventry detection range varies between sources, with figures from roughly 8 to 13 miles appearing in different accounts; the National Library of Scotland gives about 13 miles, later extended to some 75 miles with a stronger transmitter.

The speeding-ticket year and exact wording vary slightly between retellings. Most sources date the episode to 1956 in Canada with a $12.50 fine; the quotation is reported with minor variations, though the "Rough Justice" poem is consistently attributed to him.

The cathode-ray idea (1916) preceded working hardware (c. 1923). Watson-Watt proposed the display concept years before reliable tubes existed, so credit for the concept and for its practical realisation should be kept separate.

Some claims about his ancestry circulate in popular accounts but are not part of the verified scientific record, and this article does not repeat them; it confines itself to his documented education, mentorship under William Peddie, and his published atmospheric radio research.