The story of RADAR Development

An H2S radar set being operated in a Lancaster 'Pathfinder' in 1943


Alan Blumlein and Radar Development

EMI and Alan Blumlein were not directly responsible for the invention of Radio Direction Finding (RDF) or Radar (RAdio Detection And Ranging), as it would eventually be known. They did however, play an increasingly important role in the development and application of certain elements that were used in the original form of the invention, as well as the improvement and refinement of H2S, one the most widely used forms of the device. Blumlein's association with the assembly and testing of what became the most effective of all the radar systems used during the Second World War, would ultimately cost him his life.

The origins of Radar - 'Sound Mirrors'

Following the air raids on London during the First World War, it became obvious to the Air Ministry that any future conflict would undoubtedly include the use of enemy bombers flying over British cities. In November 1932, a speech was given in the House of Commons by Stanley Baldwin, in which he concluded that in any future war, expenditure on deterrents against attacking aircraft was a waste of time as "...the bomber will always get through".

Though a widely held opinion at the time, thankfully it was not the belief of a few, determined men who felt sure that some technology, perhaps unknown at that time, could be brought to bear on the problem. During the First War, several forms of sound detector had been used to locate enemy gun positions. These small dish-shaped detectors were now considered as possible detectors for aircraft and were to be scaled up accordingly. Experiments were carried out in great secrecy along the cliff-tops near Dover with a variety of concrete sound reflector mirrors that had been invented by Dr. William Tucker. Through the late 1920s and into the early 1930s a series of massive, long-range aircraft detector systems, were constructed along the coast from Romney Marshes, near Hythe towards Dungeness.

These 'Sound Mirrors'  at Hythe, near Dungeness were built in the early 1930s as aircraft early warning listening devices. They are massive, the wall in the background is over 200 feet long

The 'sound mirror' above is a 200-foot long wall

Built of reinforced concrete, these enormous 'ears' would, it was hoped, be large enough to pick up the noise from an approaching, but still distant aircraft, and focus the sound by means of a probe placed at the centre of the dish to a central listening position. This probe was nothing more elaborate than a collecting horn for the amplified sound collected by the huge dish. From this, it was expected, a bearing could be determined.

This 'Sound Mirror' dish is over 40 feet in diameter and was built in the early 1930s when aircraft travelled no faster than 200 miles an hour

This is one of the smaller 'sound mirrors', but is still over 40 feet in diameter

The massive dish itself was nothing more than a huge amplifier, with the operator listening at the base of a periscope tube, down which two sound tubes fed directly into a stethoscope-like apparatus. The listener would then wait for the approaching aircraft, take a bearing and pass the information on to headquarters nearby. When two or more bearings were taken from several sound detectors along the coast, the direction of the aircraft could be calculated.

Rear view of the same 'Sound Mirror'. These giant concrete monoliths are considered as important today as Stonehenge or Westminster Abbey and are protected as such

There was however, an unforeseen problem with the system. Not only did it pick up the sound of an approaching aircraft, there was nothing to stop the dish from picking up and amplifying the sound of everything else on Romney Marshes. This included sheep grazing, passing cars and seagulls flying overhead.

In summer, the 200-foot wall of one of the mirrors was often used as a giant wind-break by picnickers; during one demonstration set-up for the Air Ministry, their officials were almost deafened by the sounds coming from a horse-drawn milk float.

The origins of Radar -

The Tizard Committee & Robert Watson-Watt

By the early 1930s, the British government, among many others, were busy putting together teams of scientists to look into the possibilities of producing 'death rays' which could potentially be used against attacking aircraft. As far fetched as it may seem now, the possibility of 'death rays' that could incinerate an aircraft and its pilot as they flew overhead, were taken very seriously and had to be investigated.

The Director of Scientific Research in the Air Ministry had enough concern about the possibility of attack from the air and the consequences thereof, that he set up a committee to "...consider how far recent advances in scientific and technical knowledge can be used to strengthen the present methods of defence against hostile aircraft"

Henry T. Tizard, Chairman of the Aeronautical Research Committee, would chair this new committee, which was to be called the Scientific Survey of Air Defence. Tizard turned to Robert Alexander Watson-Watt, Superintendent of the Radio Research Station, part of the National Physical Laboratory (NPL) at Datchet, near Slough, in Berkshire for advice.

Robert Alexander Watson-Watt - the inventor of Radar Arnold F Wilkins who, with Watson-Watt produced the first working Radar system

Robert Alexander Watson-Watt and Arnold F Wilkins

Tizard and Wimperis put the question to him: 'Could such a death ray be constructed and used against aircraft?' Watson-Watt put this question of whether a death ray could be built or not to one of the members of his staff at NPL, Arnold F. Wilkins who was charged with calculating how much energy would be required to damage an aircraft, or its crew, and if such a ray was possible could it have already been produced?

Wilkins investigated the possibility of such a ray and concluded that while in theory it was possible, the power required to make it effective would be so prohibitively high that he considered it quite impossible that such a device could be built. Arnold Wilkins reported his findings back to Robert Watson-Watt and the two men concluded that in effect this was what they had expected. Watson-Watt reported back on 4 February 1935, to Tizard and Wimperis that there was no possibility of a high energy ray harming the aircraft or the aircrew.

Once this had been circulated to the members of the committee, A. P. Rowe (as Secretary of the Committee) approached Watson-Watt on 6 February 1935, to see if he could help them with their inquiries further. Robert Watson-Watt then asked Arnold Wilkins how he felt they might be able, if at all, to help the Air Ministry with their task.

As it happens, some years before this, some British Post Office engineers had noticed that an aircraft, flying through an experimental high frequency beam, had caused the beam to 'flutter' a noticeable degree. The matter had been reported in a Post Office report which, while it had not received wide circulation, had come to the attention of Arnold Wilkins who had been working at the time with Watson-Watt at the Radio Research Station.

Wilkins remembered this report and thought that it might be used as the basis of a system for detecting aircraft. Watson-Watt was sufficiently interested to ask him to calculate the possibility of using this and, after some work, Wilkins came back with the conclusion that it was quite possible to develop some form of aircraft detection system given the right equipment. It seemed that the probability of an aircraft, re-radiating a radio signal aimed at it back to the source, was very high.

Robert Watson-Watt drew up a document of the results of Arnold Wilkins' work to report back to Tizard, Wimperis and Rowe on Tuesday, 12 February 1935. The report was entitled 'The Detection and Location of Aircraft by Radio Means', and in it Watson-Watt wrote his now famous memorandum that "Although it was impossible to destroy aircraft by means of radio waves, it should be possible to detect them by radio energy bouncing back from the aircraft's body"

At a meeting on Wednesday, 13 February 1935, Air Vice Marshall Dowding was at first rather unimpressed with the calculations which, after all only showed the vague possibility of such a detection system working. However, he felt that if a practical demonstration could be arranged, and the mathematics that Arnold Wilkins had concluded in the report proved in principle, it might sway his conclusions. It was decided to carry out a series of tests.

Earliest Experiments - 1935

The initial demonstration was to take place on Tuesday, 26 February 1935, just 13 days after the meeting at Farnborough, which indicates the urgency with which The Air Ministry was treating the matter. The RAF loaned a Handley Page Heyford bomber (K6902) for the experiment to act as a 'target' to be tracked.

This is a Handley-Page Heyford Bomber which was used as a 'target' for the first Radar tests carried out in February 1935. The Heyford was a lumbering giant, considered obselete even before it went into service with the RAF as the last biplane bomber. For the purposes or the Radar experiments however, it proved ideal as it had a top speed of just 142mph, and therefore provided a stable, slow flying target

The Heyford was a slow and lumbering aircraft which, having first flown in 1930, was already some years out of date by 1935. As an aircraft design it was remarkable for few reasons, perhaps the most obvious of which was it was only capable of a maximum speed of 142 mph; it was also the last heavy bomber of the biplane design to serve with the RAF. For the purposes of the test however, with a wing span of 75 feet, it did provide quite a large object to 'aim at' in the sky.

The test was to be carried out in a field outside the little town of Weedon, near Daventry. The Heyford was instructed to fly on a path between Weedon and the BBC transmitter at Daventry. The detection equipment used consisted of a rather large receiver which was fitted with one of the early oscilloscopes, all of which had come from the laboratory at National Physical Laboratory, and tuned to the 49-meter wavelength that the BBC transmitter worked on.

The equipment was loaded into the back of a small van and driven on the evening of Monday, 25 February 1935, to the field, where Arnold Wilkins and an assistant prepared, in the cold and the dark, for the test the next day.

The pilot of the Heyford, Flight Lieutenant R. S. Blucke, took off from Farnborough the next morning, and climbed to 6,000 feet and started to fly the course on his flight plan.

In the van Arnold Wilkins and his assistant tuned their radio receiver to the frequency of the BBC transmitter at Daventry. As the Heyford bomber flew overhead, the steady signal of the transmitter which was being received and displayed on the oscilloscope, began to move up and down, indicating that a measurable amount of radio energy was being reflected from the aircraft above.

The Air Ministry men in the van watched as the signal indicated the aircraft in their vicinity, they were able to track it for nearly five minutes (which corresponded to a range of approximately eight miles). The experiment was a complete success and had proved conclusively that detection of aircraft with radio means was possible.

From that first test, an initial sum of 10,000 was granted to continue the work, staff were drawn from the people at the Radio Research Station and these included Watson-Watt and Wilkins of course. Radio Detection Finding (RDF) as it was known, was immediately shrouded in the highest level of secrecy - Radar, had been discovered.

From 'Chain Home' to H2S

Following the success of the initial February 1935 demonstration, the team of early RDF developers had now moved to the remote site of Orfordness, on the Suffolk coastline, 90 miles Northeast of London. Here they began the erection of the first experimental radar system. In mid-June 1935, they had succeeded in detecting radar echoes from a flying boat at a range of 17 miles, and by September the range for the detection of aircraft had increased to 40 miles. By the end of 1935, they had increased the range so that they could detect aircraft as far away as 80 miles.

In March 1936, the Orfordness group were moved to Bawdsey Manor a little further down on the Suffolk coast. By this time plans were being put into action to construct enormous radar chain of detection aerials all around the eastern coastline of England and Scotland. The first of these were built between June 1936, and June 1937, and became part of the system that would eventually become known as the Air Ministry Experimental Stations, Type One, or 'Chain Home' (CH).

The revolutionary 'Chain Home' or CH chain of Radar transmission and reception towers were built around the English coastline just in time. They proved invaluable to the operations defence systems during the Battle of Britain in the summer of 1940.

Chain Home consisted of a series of enormous towers, 300 feet high which started to appear all along the coastline of Eastern Britain. It was the Chain Home system which was used to such dramatic effect during the Battle of Britain in 1940, to guide RAF Fighter pilots towards incoming German bombers.

Later in the war, a radar system was required to aid Bomber Command to find and identify targets in Germany. This was the system which became known as H2S. H2S produced a map-like image of the ground below, allowing quick identification of an area and even specific targets.

An actual H2S Radar image of Frankfurt taken aboard a Lancaster 'Pathfinder' during a raid in Februar y 1943 This shows how H2S Radar 'mapped' out the ground below and any features such as towns and rivers showed up on the screen

Alan Blumlein was head of the EMI team which was responsible for developing electronic circuitry for the H2S radar programme. It was while working on H2S that Blumlein and several of his colleagues were killed during a demonstration flight in a Halifax bomber.

Despite the loss of Alan Blumlein and other key members of the H2S development team, the project was completed. H2S went on to become one of the most important radar developments of the Second World War, allowing accurate bombing of enemy targets with a precision never before achievable.

It has often been said that the atomic bomb ended World War Two, but radar won it.

If that is the case, then H2S was the most important of those radar systems which won the Second World War, and it was Alan Blumlein's input to the development of H2S that was critical.

On Tuesday, 10 September 2002, a memorial was unveiled by Sir Bernard Lovell,
dedicated to the RAF Aircrew, Scientists, Engineers and Civiliam Personnel
who lost their lives in the furtherance of Radar Research between 1941-1957.

Details of this memorial can be found using the link below:

Defford Memorial Unveiling 2002

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