Secret Weapons (31 page)

They took out patents on this remarkable new device, and in June 1904 the detector was demonstrated at a shipping conference in Rotterdam. The Telemobiloscope used a spark transmitter operating on a wavelength of 15.7–19.7in (40–50cm). The spark gap was submerged in oil to prevent it from burning away and the radio beam was emitted from a reflector shaped like a cone. To prevent a stray signal from some other transmitter from triggering the alarm bell, there was a time delay built into the circuitry so that the bell did not ring when the first signal was detected, but only when a second pulse was registered. This reduced the likelihood of a false alarm. Using this device, ships could be detected by simply aiming the beam in a given direction. Although there was no timing device to detect the delay between sending and receiving the signal (which would have given an immediate indication of the range) Hülsmeyer managed to show how to obtain a rough idea of the distance of the ship. The beam could be moved up and down, and – once you knew the height of the transmitter above the surface of the water – it was easy to work out the range.

Hülsmeyer and Mannheim were delighted with their success and felt that their time had come. Details of the invention were sent to the Naval office and also to commercial shipping companies, but nobody seemed interested. Their hopes were dashed, and the Telemobiloscope remained a mere curiosity. A similar device, which detected radio beams bounced back from the surface of the ground, was invented by R. C. Newhouse at the Bell Laboratories in the United States. This was patented in 1920, and it later gave rise to an altimeter worked by radio (rather than air pressure). The first British patent for what was called radio location was taken out by L. S. Alder for His Majesty’s Signal School in 1928, and the Italian wireless pioneer Guglielmo Marconi – who knew that one could use radio to detect a moving object – demonstrated a device that could detect distant objects in 1933.

This was the year when Hitler swept to power over Germany, and the emergent German Navy began to investigate harnessing the power of radio detection or
Funkmesstechnik
. In the following year, research started in Russia and successfully detected aircraft up to 55 miles (88km) distant. Nothing further happened at the time, though a French vessel in 1935 demonstrated a radio beam as a method of avoiding collisions, and this
Barrage Electronique
system was used early in World War II.

And so, by the mid-1930s, there had been a range of different developments that allowed observers to penetrate fog or to detect ships in the darkness of night. Italian, German, British and American research had all played their part in harnessing the effects first observed by Hertz in the Victorian era. Even before World War I it had been possible to detect an otherwise invisible ship, using marine radar, even though few were interested in the idea. And since the time of World War I the directional use of sound detection had been used to give warning of distant aircraft. A combination of the two – detection funding from a transmitted pulse of sound – gave rise to sonar, which was developed by separate Canadian, British and American researchers starting in 1912.

As war began to loom, increasing efforts were directed to defending Britain from attack. Robert Watson-Watt was a meteorologist who had studied the detection of lightning through the radio interference that was caused by the discharge, and he was approached about stories that were beginning to filter out from Germany. The Nazis, it was said, had a death ray. They could beam a radio transmission and wipe out populations at a considerable distance. Britain needed one too, it was agreed, and Watson-Watt must be the person to approach. It did not take him long to calculate that it was impossible, and he wrote a report to defuse the concern felt in official circuits. At the end, he added a note on a different problem that was ‘less unpromising’ than a death ray. This was the detection of objects by reflected radio waves. A report on that, he said, will be ‘submitted when required’.

Watson-Watt did not invent the idea of detecting objects by reflected radio signals. This had long been established as a way of detecting shipping, where the metallic mass reflected the beam, but what about using this approach on aeroplanes? They were not heavy steel objects, and were often made of cloth and wood, but could they still reflect a radio beam? In February 1935 Watson-Watt wrote a top secret memorandum for the Air Ministry in London. He entitled it
Detection and Location of Aircraft by Radio Methods
. This was a radical new departure, and the Air Ministry asked for a demonstration. Within weeks, an experiment was set up at Litchborough, near the BBC shortwave transmitters at Daventry. Two transmitters were set up so that their signals cancelled each other out. Anything that interfered with the signal would deflect a spot on an oscilloscope screen. Only three people were involved: Watson-Watt and his assistant Arnold Wilkins, with a representative of the Ministry, A. P. Rowe. A Handley Page Heyford bomber was chosen as the first target. The Heyford was a biplane built in 1930, and was the last heavy biplane to be used by the Royal Air Force. Its wing-span was also exactly one-quarter that of the wavelength of the radio beam, which would maximize the chances of generating a positive echo in the signal. Flight-Lieutenant R. S. Blucke was the pilot that day, and he took off from the airfield at Farnborough and climbed slowly to 6,000ft (1,830m).

When he reached Daventry, the team on the ground saw the oscilloscope signal suddenly begin to flicker. The three men watched until the signal returned to normal when the aircraft was 8 miles (13km) distant. The principle was proved – not only heavy steel ships, but even lightweight aircraft, could be detected by the reflections of a radio beam. Within four short years, the system was refined until planes could be detected at a distance of 100 miles (160km) and work began on erecting a series of detector stations. This became the Chain Home network, known as CH for short, and it was fully operational in 1937, long before World War II broke out. This was the first radar system detecting aircraft in the world. When the war began in 1939, many nations were harnessing the same effect: France, Germany, Hungary, Italy, Japan, Netherlands, Russia, Switzerland and the United States were all investigating radar systems of their own.

The true value of radar was recognized during the Battle of Britain in 1940–41, when the system gave advance warning of attacks, and knowing the direction of incoming German aircraft enabled fighters to be dispatched in good time. Reports of planes being detected by the CH stations scattered across the south of England and the Isle of Wight, were sent by telephone to ‘filter rooms’ which brought all the results together. Orders were then issued to the airfields to coordinate a response by British fighters. The Germans failed to grasp the way the CH system worked, and did not investigate how to jam the transmissions.

Radar was not always a success. We have already seen, good radar reflections from incoming Japanese warplanes were detected prior to the attack on Pearl Harbor – but radar was relatively new, as were the observers, and so the all-important advance warning was fatally disregarded. Radar detectors were subsequently erected by the Germans on the coast of northern Europe, facing England. In February 1942, one of their Würzburg radar stations was detected by British reconnaissance near Bruneval in Normandy and close-up photographs were taken in a daring daylight raid. The British realized that the obvious answer would be to raid the radar establishment and bring the important components back to England. The idea was quickly approved, and R. V. Jones was the first to volunteer to go along and act as the technical specialist – but the authorities decided against sending anyone with specialist knowledge. If captured, they would be aware of details that the Germans could perhaps extract.

The plan was for this audacious raid to be carried out by ‘C’ Company of the 2nd Battalion, 1st Parachute Brigade commanded by Major John Frost. Their specialist would be radar operator Flight-Sergeant C. W. H. Cox. None of the men was told anything about the raid until the last minute, and training went on with scale models of the enemy terrain and with trials on the beaches of southern England.

On the night of 27 February 1942 the teams were dropped by parachute from Whitley aircraft flying at just 600ft (180m). The beach was secured, and teams rushed to the villa where they found a single German soldier guarding the equipment. German troops from a nearby pillbox were firing into the site as the British troops disassembled the Würzburg radar aerial, removing the important components which were all packed and taken quickly to the beach. There were problems making radio contact with the Navy, who were supposed to be ready to collect the men and their spoils, but had encountered a German warship and had to take evasive action. The German pillbox had been silenced and red flares were shot into the sky – at which point the Navy appeared in rough seas to retrieve the teams. Under enemy fire six landing craft arrived to collect their precious cargo. The ship was escorted back to Portsmouth Harbour by Royal Navy destroyers with RAF Spitfires flying overhead; the patriotic song
Rule Britannia
was played at high volume from loudspeakers. The raid was entirely successful. The airborne troops suffered only a few casualties, and the pieces of the radar they brought back, along with a German radar technician, allowed British scientists to understand German advances in radar and to create counter-measures to neutralize those advances.

Brave members of the French resistance continued to supply information to Britain and it was soon discovered that all German radar stations operated on a small number of frequencies, and they could easily be jammed. When a huge and devastating Allied bombing raid on Hamburg was planned for July 1943, fragments of metallic strips were dropped – once again, exactly one-quarter as long as the wavelength of the German radar beams, to maximize reflections – and the signals from the radar stations were completely obliterated. This chaff was known as ‘window’ by the Royal Air Force and had been independently discovered in Germany, where it was known as Düppel. It is a sign of the confused strategic planning by the Nazis that, having pioneered the use of reflecting chaff, the Germans did nothing to prepare themselves for its use by the Allies.

The Germans lacked the ability and knowledge to manufacture radar systems in which the radio beams could be tuned to a desired frequency, and this capability gave the British superiority in this vital area of defensive warfare. The early radar trials in Britain used a frequency of about 10MHz and the Chain Home stations began at 20MHz and later extended their range up to 70MHz – but the tracking radars operated at 200–800MHz. In 1940 the Americans began to use a cavity magnetron transmitter which went from the megahertz range up to gigahertz frequencies. It was small enough to fit into aircraft, and the H2S radar which was used by United States Air Force bombers had a frequency of 3GHz. It could show the details of the ground beneath the aircraft with unprecedented accuracy – but it was decided never to use it over Germany. Allied intelligence had reported that the Germans believed 800MHz was the highest frequency that radar could use, and it was feared that – if an American plane was shot down, and the secret of its radar was discovered by the Germans – the balance of power could radically change.

In the event, this proved to be a groundless fear. In the spring of 1943 an American bomber was brought down near Rotterdam, Netherlands, and the onboard H2S radar and the intact magnetron fell into German hands. They set out at once to reconstruct their own version, code named Rotterdamgerät, but the first examples were manufactured only when the war was nearing its end.

Installations of British radar detectors on Royal Navy ships allowed them easily to detect German submarines on the surface of the sea, and so the Germans worked on methods of preventing their U-boats from generating an echo, so they could thus escape detection. They soon found that a mixture of rubber and carbon painted onto a submarine’s superstructure greatly diminished the strength of its radar signature, and they tested it in a dry dock until they had perfected the ideal recipe. Surprisingly, the British warships continued to detect the submarines as though nothing had happened. The reason was simple – when wet with seawater, the protective layer no longer worked and radar detection could function as normal.

We must not dismiss the German idea out of hand, however: this was the origin of what we now know as ‘stealth technology’. Once again, a development from World War II underpins a crucial aspect of present-day warfare.

Radar in Britain had a decisive effect on the conduct and duration of the war. Following enemy aircraft and ships that were otherwise invisible was of crucial importance. The Chain Home network was even shown to be able to detect V-2 rockets long before they reached the British coast and, although nothing could be done to prevent their arrival, this is historically significant as the first ballistic missile radar detection system in the world. These systems are now everywhere. It is also important to note that Hungarian scientists used their own radar to bounce signals off the moon in 1944. This was the first time it was ever achieved, and they accurately measured the distance of the moon from the earth for the first time in history.

Radar was firmly established and had become refined by the end of World War II. During the Vietnam War of 1955–75, anti-radiation missiles were developed which would home onto the beam emitted by a radar transmitter and destroy the installation, thus using the radar against itself. As devices became increasingly compact, radar speed detectors entered service with the police force. And so we can look back at the stimulus that World War II gave to the development of radar – and can bear in mind that the same principle had been used to detect shipping before World War I began. Radar has enjoyed a lengthy history. It can now entrap you on a highway, it is an integral part of global transportation, and it promises to have an illustrious future.