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story:Science in war

scene:The radar war

The radar war
In September 1940 Winston Churchill visited the control room at RAF Northolt to watch the air battle in progress. It was the height of the Battle of Britain. He later wrote,
'All the ascendancy of the Hurricanes and Spitfires would have been fruitless but for this system which had been devised and built before the war. It had been shaped and refined in constant action, and all was now fused together into a most elaborate instrument of war, the like of which existed nowhere in the world.'
Winston Churchill, The Second World War.
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Spitfire Mark I aircraft in echelon. Pre-war RAF training laid stress on accurate formation flying but, as the air war progressed, the RAF learned to fly in looser groups, like the Luftwaffe.
Pilots and gunners of Defiant aircraft from No.264 Squadron relaxing between sorties.
The Chain Home masts at Poling, Sussex; these played a vital role in the Battle of Britain.
The effect of radar
The effect of British early warning radar was twofold. Clearly the major benefit was to enable the defending force to find and attack intruders. The other was to reduce the wastage of aircraft and pilots. Without radar, the fighter force would have been spread thin in 'standing patrols', flying ready at height. As soon as fuel ran low the patrol would have to land, perhaps without seeing an enemy, and fresh aircraft would take off.
This process would have wasted precious high-octane fuel, pilot time, aircraft and engines. Fighter Command in the Battle of Britain could not have sustained such an effort. Without the radar chain 'The Few' would have been too few.
Images with the text:
Battle of Britain, 1941 by Paul Nash. Nash has captured a moment at which the 'aerial ballet' of the battle has been made visible by the condensation trails from the aircraft.
A pilot running to his Spitfire (No.64 Squadron) after hearing the 'scramble' warning, August 1940.
A Messerschmitt Me 109 shot down in an air battle over Ramsgate, August 1940.
The birth of radar
British radar came about as a result of growing concern about air attack and German rearmament. In 1934 the Air Ministry created the Committee for the Scientific Study of Air Defence, which was chaired by Sir Henry Tizard, its most trusted scientific adviser.
Just four weeks later a trial was arranged at Daventry, using an existing transmitter and receiver. An RAF Heyford bomber had been instructed to fly in the vicinity and was clearly detected. Although the aircraft had been only eight miles away, more experiments were financed through Tizard's support and moved to an isolated First World War weapons testing site at Orfordness, Suffolk, in May 1935.
By June 1935, when the Tizard Committee visited, the detection range had been improved to 40 miles. Now the group was outgrowing the Orfordness site and moved to Bawdsey Manor a few miles away on the mouth of the River Deben.
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Sir Henry Tizard trained originally as a chemist, but displayed a unique combination of scientific knowledge, a resolute practical attitude and an understanding of air problems gained in the First World War when he flew and tested fighting aircraft at Farnborough and Martlesham.
Images with the text:
Sir Henry Tizard trained originally as a chemist, but displayed a unique combination of scientific knowledge, a resolute practical attitude and an understanding of air problems gained in the First World War when he flew and tested fighting aircraft at Farnborough and Martlesham.
The receiver used for the first British radar experiment (today in the Science Museum). It was a modified short-wave communications receiver.
Robert Watson Watt, head of the Radio Research Station at Slough, had been asked about the feasibility of developing a beam weapon or 'Death Ray' to damage enemy aircrew or engines. Watson Watt told Tizard's committee that the energy required to produce damage was far beyond anything achievable at the time. However, he believed that detecting an intruder aircraft by transmitting a stream of radio pulses and listening for the 'echo' was now just possible technically.
Oil painting of the first radar trial by artist Roy Huxley. On 26 February 1935 the receiver was taken, in a small van, to try to detect a Handley Page Heyford bomber. The bomber had been directed to fly through short-wave transmissions from the nearby Daventry radio transmitter.
Oil painting of the first radar trial by artist Roy Huxley. On 26 February 1935 the receiver was taken, in a small van, to try to detect a Handley Page Heyford bomber. The bomber had been directed to fly through short-wave transmissions from the nearby Daventry radio transmitter.
Robert Watson Watt and his team calculated that if a short radio pulse was transmitted towards an aircraft, it should just be possible to detect the weaker reflected echo. However special trnsmitter and receiver equipment needed to be developed. This diagram shows a set operating with a dish antenna and shorter wavelengths than Chain Home, as in German Wurzburg sets.
Map of portion of the east coast of England showing Orfordness and Bawdsey in Suffolk.
Radar at Bawdsey
At Bawdsey the first aerial mast was in action by March 1936 when the laboratory tracked a single aircraft at a range of about 80 miles. In September, Bawdsey took part in the first RAF air exercises using radar. By May 1937 radar was thought to be capable of real operations in war.
In June 1939, shortly after becoming Prime Minister, Winston Churchill visited Bawdsey to see 'this wonderful development'. He wrote: 'I found my visit to Martlesham and Bawdsey under Tizard's guidance profoundly interesting . . . and encouraging.'
These demonstrations, and Tizard's confidence, inspired Britain to take an immense gamble on the system. C. P. Snow noted, 'within a very short time the Tizard Committee were asking for millions of pounds and getting it without the blink of an eye. Two successive secretaries of the Cabinet, Hankey and Bridges, did much more than their official duty in pushing the project through.'
Though radar developments were encouraging, Tizard saw that it was not the complete answer. New techniques for directing fighters, communicating by radio and keeping track of enemy and friendly aircraft, would be needed. This was a revolution in tactics. Indeed Tizard had urged special air interception exercises (the Biggin Hill experiments) from February 1936, even before the radar sets were ready.
Fighters practised interceptions on 'dummy' intruders flying known routes to train controllers and pilots in the new techniques of communication and control.
Bawdsey was the prototype and starting point for the chain of stations that were then built, first to cover the Thames Estuary and eventually ringing the entire coast.
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Bawdsey Manor and the first experimental radar masts in Britain. Bawdsey became the model for all the other Chain Home stations, which ringed most of the coast by 1940.
British radar growth
The radar chain developed between 1935 and 1941. September 1935 coincides with the start of the Bawdsey experiments and September 1940 reflects radar cover at the time of the Battle of Britain.
Hugh Dowding is best known for commanding the RAF fighter force during the Battle of Britain, but he was in charge of research and development during the birth of radar and the creation of a parallel system for fighter communication and control. These were set up with incredible speed, partly because, as defence scientist R. V. Jones recorded, 'there was in the Royal Air Force in 1935 a cadre of officers of exceptional outlook, who were prepared to work with the scientists with the utmost urgency...'
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Map of radar cover between 1935 and 1941.
Hugh Dowding is best known for commanding the RAF fighter force during the Battle of Britain, September 1940
The technical challenge
The initial land-based radar system was developed by Robert Watson Watt's team. It came to be called the 'home chain' or 'Chain Home'.
The Chain Home system ringing the coast was the first integrated air defence system, a distinctive and triumphantly successful British innovation.
It used transmitter and receiver designs adapted from existing communications and broadcast technology and was, in effect, a brilliant improvisation that relied to a quite substantial extent on existing electronics technology. Although it used what broadcasting engineers called 'short wave', the signals were relatively long by later radar standards. This made the large aerials and supporting aerial tower installations necessary.
Radar in Germany
By 1941 it had become important to know whether Germany also possessed a radar system. Analysis of German radio transmissions and photo-reconnaissance signals gradually revealed the existence of two types of set: Freya and Wurzburg. These worked on shorter wavelengths than the British Chain Home system and, in some respects, were technically more advanced. They were not, however, integrated into a national air defence system until later.
One Wurzburg set in France had been spotted from the air at Bruneval, near the coast at Le Havre. In an audacious commando attack, important components were taken from it and brought to Britain (with a captured operator) to allow evaluation of the set and its capabilities.
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The Filter Room at Fighter Command headquarters at Bentley Priory, Stanmore, from where the Battle of Britain was fought. The 'sector clock' was used in conjunction with coloured markers on the map board to show how recent were the displayed aircraft positions.
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Women's Auxiliary Air Force (WAAF) personnel were vital in the filtering and plotting rooms, moving markers with 'croupiers' rakes' to show the positions of German and British aircraft and the emerging pattern of the battle.
Women's Auxiliary Air Force (WAAF) radar operator observing aircraft traces on the cathode-ray tube.
The 'blip' on the cathode-ray tube of the indicator unit shows an echo reflected from an aircraft.
Reconnaissance photograph of the Wurzburg set at Bruneval, near Le Havre, in 1942. The discovery of this set prompted the commando raid.
A Telefunken valve, part of the haul of Wurzburg parts brought back from the Bruneval Raid in February 1942.
Miniaturising radar
The Chain Home system was accurate to about three miles: close enough for a fighter pilot to spot his quarry in clear weather. But as the German attack turned from the daylight attacks of the Battle of Britain to night bombing of London and other cities, much more accurate radar direction was required: at night fighter pilots needed to be guided to about 300 metres from the intruder. The suggestion was to build on-board radar sets.
It seemed ambitious, even to the electronics boffins, to expect radar, then reliant on high aerial towers and room-sized transmitter and receiver sets, to be miniaturised. Yet by the winter of 1940-41, air-interception sets (A. I.) had been fitted to night fighters. Sir Bernard Lovell, recalling those days, suggested that the fantastic speed of development (sometimes only months from laboratory trial to combat aircraft) was possible then because no one ever asked how much it would cost.
The question, he recalled, was always 'Can you do it and when can we have it?' However there is no doubt that this rapid development was also made possible because the radar work acquired exceptional people who were totally committed to its success. One recalled it as 'the most thrilling, the most challenging education. . . . I see it now as the outstanding experience of my life'.
To make on-board aircraft radar work well, high power and short wavelengths (high frequencies) were needed. Contemporary electronic valves were not up to the task of generating these. The key to success was the magnetron, devised at Birmingham University in February 1940 by John Randall and Henry Boot.
Radar against submarines
One almost unexpected benefit of the airborne radar programme was the discovery that these sets could be used to detect ships, even surfaced U-boats. At one point it had seemed that the sinking of merchant shipping could lead to a British defeat, but in the first half of 1943 radar-equipped aircraft of Coastal Command were starting to destroy surfaced U-boats with lethal efficiency. The total amount of merchant shipping being sunk fell from 700,000 tons for March to under 100,000 tons by August.
Aiming bombs with radar
Another discovery by the radar teams was that airborne radar was effective in showing up cities and buildings from above, even through heavy cloud. From early 1943 radar bombsights, codenamed H2S, were being fitted into British night bombers, contributing to the almost total destruction of Hamburg in July.
Images with the text:
The original magnetron. This was one of the inventions taken to the USA by the Tizard Mission in September 1940. The powerful American electronics industry soon began quantity production of airborne radar for British and US forces.
German U-boat under attack from the air with depth charges. At first it was thought that 'scatter' (echo returns from the sea) would defeat submarine detection by radar, but surfaced U-boats proved to give a detectable signal and successful attacks against U-boats increased. To counter losses, U-boats were fitted with a radar detector to warn of searching RAF aircraft. A change to newer, shorter wavelength sets defeated this countermeasure.
The rotating aerial scanner and cathode-ray-tube indicator for H2S Mk Iic.
Cathode-ray-tube indicator and controls of the H2S system installed in a bomber aircraft.
Hamburg after the firestorm. In one of the most terrible attacks in modern warfare, Hamburg was almost totally destroyed by three raids on 24, 27 and 29 July 1943. The RAF Bomber Command force was led by 'pathfinder' aircraft equipped with H2S radar target-finding sets.
Today the once top-secret magnetron is a key component of every domestic microwave oven, heating and cooking food by radio energy.

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