FIRESTORMS FROM THUNDERSTORMS

See Also: RADIO Guglielmo Marconi; THE SECOND WORLD WAR; WEATHER Lightning

During the First World War thunderstorms were a potentially fatal menace to airborne Royal Flying Corps personnel. Finding a means of being able both to identify the location of such storms and to plot their movement became a priority research field for the staff of the Royal Aircraft Factory at Farnborough. By the end of the conflict, it was possible to identify thunderstorms at a distance of several hundred miles. One of the scientists who worked upon the problem was Robert Watson-Watt. During the early 1920s cathode ray oscilloscopes became available. He was able to demonstrate that they could be used to produce a superior thunderstorm detection system.

In 1933 the Nazis seized control of the German state. In Britain the Air Ministry responded to this development by deciding to improve United Kingdom's defences against aerial bombing.¹ Watson-Watt, who by then was based at the National Physical Laboratory, was asked to investigate whether enemy bombers could be destroyed by a high-energy radio ray. He delegated the task to his assistant Arnold Wilkins, who soon proved that such a weapon was not viable.

During their discussions about the matter, the junior colleague mentioned something that his boss had not heard of before. This was that some Post Office research engineers had noticed that, when an aircraft flew in proximity to a V.H.F. transmitter, the device's signals would oscillate. Watson-Watt appreciated that this phenomenon had the potential to create a system that could detect the location of planes at a distance. He realised that it might be possible to create such a technology by utilising the techniques that Edward Appleton had developed in 1924 in order to prove the existence of the upper atmosphere's Heaviside layer.²

In early 1935 Watson-Watt submitted a report to the Tizard Defence Committee about the potential for creating a radio location system. A fortnight later a secret field trial was conducted. This indicated that the technology had the potential that the boffin had stated that it might have.

By the end of summer 1936 the Air Ministry had established the Bawdsey Research Station near Felixstowe. Watson-Watt was appointed to be the facility's superintendent. He had not only had the basic idea for radio location but he also proved to be able to recruit scientists and engineers who were capable of realising the system. He won a series of bureaucratic struggles that secured the material wherewithal to develop it. Tizard was supportive of his efforts. The latter appreciated that it was not only possible to create the technology but that there was also a need to put in place procedures within the Royal Air Force that would enable its operational effectiveness to be optimised. He was active in ensuring that they were created.

In 1938 the first series of radio location stations started operating along England s East Coast. However, the system was utilising the 50m wavelength. This meant that it was unable to detect aircraft after dark. Tizard appreciated that it might be possible to decrease the wavelength. This would both improve the technology's operational capacity and reduce the size of individual units. He pursued the matter assiduously.

In summer 1938 Watson-Watt was promoted to a position within the Air Ministry s central bureaucracy. This was fortunate. His temperament was suited to contending with external elements in an adversarial manner. However, he was not always adept at managing interpersonal relationships with his colleagues. His successor as superintendent, Albert Rowe, possessed the latter skills. He fostered a workplace culture in which subordinates felt free to raise with their supervisors any matter that they felt that they should.³

Mark Oliphant was an Australian-born nuclear physicist who had worked under Lord Rutherford at the University of Cambridge's Cavendish Laboratory. He had moved to Birmingham University. In the late summer of 1939 he was taken to see the radio location stations. He appreciated that microwave radiation technology had the potential to improve the system's operation. He assigned the research students Harry Boot, J.T. Randall, and James Sayers to the task of developing a magnetron-based microwave generator. By early 1940 Boot and Randall had built a cavity magnetron that made possible a radio location system that operated on a 10 cm wavelength. This not only improved the accuracy of radio location beams but also made possible the manufacture of transmitters that were light enough to be carried on board aircraft.⁴

Lorenz LEF was an airfield system that enabled aircraft to be landed when they were being flown blind at night or in bad weather. It had been developed by C. Lorenz A.G., a Berlin-based electronics company.⁵ In 1937 its technology had been adapted to create a beam radar bombing direction system. This had been enhanced further to become Knickebein ( crooked leg ), which enabled planes to fly out along a ray of energy that was transmitted from the continent. When it intersected with a second beam the aircrew knew they should drop their bombs. The Luftwaffe regarded the broad-area illumination approach to radar as being primitive .⁶

Hans Mayer was the Director of Siemens's research laboratory in Berlin. In his position, he was privy to a wide-range of information about the ways in which the Nazi regime was seeking to have electronics applied to the development of military technology. Covertly, he compiled a dossier about what he knew. In November 1939 a copy of it was delivered anonymously to the British Embassy in Oslo.

In London the material became known as the Oslo Report. The remarkable breadth of its information prompted a degree of scepticism in most of the people who saw it. That such a revelatory leak should have occurred at such a time seemed to be too good to be true. As a result, it was regarded with wary indifference. However, at the start of the war Reginald Jones, a Royal Aircraft Establishment scientist, had been appointed to work in the Air Ministry's Intelligence Section. He had the technical expertise to realise the veracity of much of what Mayer had sent. At his urging, the Ministry started to treat the dossier's contents as being genuine.

The R.A.F. suffered heavy losses during the Air Battle of Heligoland Bight (18 December 1939). Therefore, the service s command opted to conduct its subsequent bombing raids only during the night. Gee was a short-range blind landing system that utilised two signals that were sent out by two airfield transmission stations.⁷ Instructions were issued that, like Lorenz LEF, the technology should be adapted so that it could furnish a long-distance, hyperbolic navigation system. By the summer of 1940 it was able to be used by aircraft that were flying at a range of up to 300 miles from its transmitters. However, the further away the planes were from them the higher they had to be if they were to avail themselves of the signals.

Jones deduced the technological origins of Knickebein. He calculated the frequency range that it was utilising. In June 1940 his computation was found to have been correct. Therefore, a series of transmission stations were established in southern and eastern England. These were able to bend the signal that the continental system was issuing. As a result, the Luftwaffe's raids began to inflict less damage than they had caused previously.

On 13 August Berlin launched Operation Eagle Attack. The fighter-protected bomber formations sought to strike at R.A.F. Fighter Command's facilities. The Luftwaffe's Intelligence Section was aware that the British had developed a radar system. However, since it did not appear to use beam technology, the mental rigidity of the Section's staff prevented them from giving the factor any weight. Consequently, the German air force's losses mounted to levels where the Operation's sustainability was put into question. In early September the Luftwaffe switched its focus from attacking airfields to bombing towns and cities. The following month it ended the campaign.

X-Ger t was a purpose-designed beam radar system. Its flaws were exposed after a set was recovered from a crashed Heinkel in November. Once the equipment had been analysed, the technology was undermined by the transmission of false beams. These prompted the German bombers to drop their cargoes prematurely.

The Oboe radio navigation system started to be introduced at the end of 1941. It was more accurate than Gee had been. It enabled bombing to become more exact both at night and in total cloud cover. However, it could only be used to direct a single aircraft. Therefore, it was employed to guide pathfinder bombers that would attack an objective. The resulting fires were used by a following formation to identify the target site. Oboe could not be jammed by the Germans with the same ease that they had been able to block Gee. However, it sent aircraft along a curved flight path - the boomerang - that the Luftwaffe could plot. Therefore, Oboe-directed aircraft were vulnerable to being intercepted.

A team of technicians that was led by Philip Dee noticed that different types of terrain returned radar signals in different ways. At the start of 1942 a Telecommunications Research Establishment research group that was led by Bernard Lovell started to develop an airborne ground-scanning radar system. At its core was the cavity magnetron.

The origins of the system's H2S name are uncertain. Lord Cherwell was Churchill's principal scientific adviser. The peer regarded the valve as being too important for one to be allowed to fall into German hands. Therefore, he tried to ensure that the apparatus was based upon klystron, which was a far less effective device. There is a story that upon one occasion he referred to the prospect of the magnetron-based equipment's development as being rotten . The Lovell group technicians were aware that the smell of hydrogen sulphide (H2S) was akin to that of putrid eggs. Therefore, they may have co-opted the formula as a moniker for the project. In July 1942 Churchill stated that an H2S should be installed in an aircraft within four months. Therefore, the baron was forced to give way.

Berlin allowed resources to be devoted to electronically countering the Allies use of radar. The German technicians had an immense advantage. Allied aircraft flew over the European mainland, whereas the Luftwaffe's planes could no longer operate effectively over Britain. Therefore, when the former were shot down their wreckage could be examined. German electronic engineers were able to keep abreast of the progress of Allied radar technology. As a consequence, they were able to create a series of systems that exploited its shortcomings. The first H2S set was installed in an R.A.F. aircraft at the start of 1943. Within a week the Germans had recovered an intact one from the remains of a Stirling pathfinder bomber.

The Luftwaffe began to pull ahead in the electronic battle between the two sides. The Naxos radar detector system used a cavity magnetron and could identify the H2S signal. This meant that German interceptors were able to locate bombers while flying blind. By the autumn of 1943 this advantage was being compounded by the fact that the number of the service's aircraft that were operating over Germany had increased markedly.⁸

Gee and Oboe's need for line-of-sight transmitters meant that they were limited in terms of the distance at which their technology could operate. Therefore, the eastern location of Berlin had meant that the R.A.F. had not been able to strike at the city with any degree of accuracy. The introduction of the H2S Mk III ground-scanning radar system enabled navigators to find the capital in all weather conditions.

Over the period November 1943-March 1944 Bomber Command launched sixteen mass formation bombing raids against the city. During these, over a thousand bombers were lost and almost 1700 were damaged. The Berlin campaign did not break the morale of the capital's residents. Nor did it have any serious impact upon the production levels of the military manufacturing that was being carried out there.⁹

The Flensburg radar system was introduced by the Luftwaffe during the spring of 1944. Its passive radar receiver technology enabled the service's interceptors to locate R.A.F. bombers that were using Monica tail warning radar technology. The latter had been in use for two years.

Ten Wehrmacht artillery pieces covered the D-Day landing sites. On 5 June the Oboe system was used to direct a thousand bomber raid against the guns. Nine of them were put out of action.

A little over a month later, the Allies received a major, unanticipated boon. R.A.F. Woodbridge was an emergency landing field that was located in Suffolk. On 13 July a twin-engine Junker 88 set down there. The plane's three crew members climbed out of the craft and were met by a landing party. Both sides were shocked by what they encountered. The German airmen were relatively inexperienced and had misread their compass by 180 . They had believed that they were touching down at an airfield in Central Europe. The men were taken into custody and the technology in their fighter was analysed by Allied radar experts.

It was soon appreciated how Flensburg had been able to tune into Monica sets. It was discovered not only that the Luftwaffe system could detect a Lancaster at over a hundred miles distance but that it could identify precisely how many bombers there were in a mass formation. The Woodbridge Junker revealed to the Allied commanders how deeply complacent they had been in their excessive reliance upon active emitting radar technology.

A series of new practices were soon introduced for Allied air crews. Of these, the most important one was not switching on their sets until their aircraft were close to their targets. The Flensburg approach of targeting a system that was being used was turned on itself. This rendered the hunter into prey for the Allied night fighters that escorted the bombing parties.

In early-and-mid 1944 Bomber Command had been losing 250 aircraft a month. By the end of the year, following the introduction of the post-Woodbridge countermeasures, the attrition rate had fallen to a fifth of that level.

In May 1945 the Oboe system was used to facilitate humanitarian missions. It guided food drops to starving Dutch civilians.

Despite the large improvements in aerial navigation, at the end of the war only half of the bombs that the Allies were dropping were landing within five miles of their objectives. Germany's principal cities had been devastated because they were large targets that had been attacked frequently rather than because of the precision with which they had been assaulted.

Location: Adastral House, 1 Kingsway, WC2B 6AN. The Air Ministry left the building in 1952. (blue, red)

The National Physical Laboratory, Hampton Road, Teddington, TW11 0LW.

¹. During the First World War, the Germans had used zeppelins to drop bombs on a number of British cities.

². In 1901 Guglielmo Marconi had been able to send a radio signal from Newfoundland. This prompted postulation amongst physicists as to how such had been possible. Oliver Heaviside and Arthur Kennelly had contended that the signal might have bounced off a layer of ionised gases in the upper atmosphere.

³. In 1940 the Bawdsey Research Station metamorphosed into the Telecommunications Research Establishment. Two years later it relocated to Malvern.

⁴. E.G. Bowen, a former Ph.D. student of Edward Appleton's at King s College, oversaw the creation of effective aircraft-born radio location systems.

⁵. C. Lorenz had become a subsidiary of International Telephone & Telegraph (I.T.T.) of the U.S. in 1930.

⁶. Generally, the German approach to radar was more practical than the Allied one was. The former ensured that their systems could be operated effectively by unskilled individuals. In contrast to this, the latter opted for a technocentric user-approach that meant that people had to undergo extensive training.

⁷. Gee had been developed by the Telecommunications Research Establishment at R.A.F. Bawdsey.

⁸. In part, this was because many of them were being redeployed from the Russian Front. This aided the Soviet Army.

⁹. One lasting impact of the campaign was that Brandenburg acquired a population of raccoons. The animals ancestors escaped after the fur farm in which they were being kept was damaged during a raid. (A separate one exists in Hesse. It was established as the result of an authorised release that took place in 1934.)

David Backhouse 2024