Engineer of the Week No.106: Joan Elizabeth Strothers (Lady Curran) (26 February 1916 – 10 February 1999)
On our annual Remembrance Day, when we remember those who died in war, today we also remember Joan Curran, a woman whose invention helped to end the 2nd World War.
Joan Strothers was a Welsh physicist-engineer who was the inventor of the UK form of the WW2 anti-radar measure known as ‘chaff’ or ‘window’.
Born and educated in Swansea, where her father was an optician, Joan won a scholarship in 1934 to study physics at Newnham College, Cambridge. Although she gained an honours degree (1937) this was still 10 years before Cambridge actually awarded any degrees to women. She then won a government grant to study for a PhD in Philip Dee’s group at the Cavendish Laboratory at Cambridge, where she excelled at practical experimental work. The Second World War intervened and the PhD was abandoned in favour of the wartime needs. Dee took the group initially to the Royal Aircraft Establishment at Farnborough, only for their section to be immediately evacuated to the physics department at the University of Exeter. Joan was in a group with her future husband (Sam Curran) led by John Coles and working on the development of the proximity fuse. They were put into Leeson House (now a field studies centre) in Langton Matravers, Purbeck, which had become a top-secret radar research centre. Their successful design of a proximity fuse, was manufactured in the USA in time to become crucial in the fight against the V2 bombs later in the war.
In 1940 Joan and Sam married and were both transferred to the Telecommunications Research Establishment (TRE) near Swanage, where Joan was assigned to the radar countermeasures group. It was here that Joan devised the technique that was codenamed Window (or Chaff), which consisted of strips of metal to fool the enemy radar. She tried various types of radar reflectors, including wires and sheets, before settling on strips of tin foil 1 to 2 centimetres wide and 25 centimetres long that could be scattered from bombers. This was first tried out during bombing raids on Hamburg, resulting in a much lower loss of Allied planes than usual. Another use was to imitate the radar reflections that would be detected from a phantom invasion force of ships in the Straits of Dover so as to distract the Axis forces as to where the D-Day landings really were.
In his obituary of their mutual boss, Philip Dee, Sam said of this period: “When my wife (formerly Joan E. Strothers) was working at TRE on radar intelligence and countermeasures she carried out personally very early in 1942 the first experiment on ‘Window’ and this proved to be an experiment of truly major importance. I remember that at home she cut up a large amount of metal foil with her household scissors and then she organized the dropping of the thin metal foil strips from an aircraft sent up from Christchurch aerodrome. She had arranged that observation at the radar detection stations on the ground should be done. The effects on the radar screens were truly amazing and it looked as if a large fleet of aircraft was present. This first demonstration of ‘Window’ was cearly of outstanding importance to the whole of radar science.”
Some WW2 historians believe that Joan Curran made an greater contribution to the Allies’ victory than her husband’s work did. Chaff is still in use today by the world’s armed forces, and its use military exercises often causes confusing images on weather forecasters’ radar.
In 1944 both Joan and Sam were sent to the University of California, Berkeley, to work under the direction of Ernest Lawrence on the separation of isotopes of uranium as an important part of the Manhattan project (the development of the atomic bomb), following from their work (and joint publications) on nuclear physics at the Cavendish Laboratories. While they were in the USA Joan had the first of their children and her work in applied physics ended. After the war her husband worked first at the University of Glasgow and then became the first principal of the University of Strathclyde. Joan’s first child was severely disabled and she spent the rest of her life campaigning for the needs of the disabled, leading to her joining the local health board, special needs housing association and also established the Lady Curran Endowment fund for overseas students.
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