It is always an advantage in battle to know what the enemy is up to. In the past the military relied on observers and spies to supply this information, but during the twentieth century technology began to play a more important role allowing the Allies to identify enemy planes, ships and submarines from a greater distance through the use of radar (Radio Detection and Ranging). Planes were first used in war for reconnaissance (1914-18) but as they became bigger and faster it became clear that planes were the weapons of the future and the threat of bombing of civilian centres grew, in 1932 Stanley Baldwin (the British Prime Minister) said that ‘the bomber will always get through’. To try to combat this scientists and technicians turned to radar.

It was in the 19^th century that Michael Faraday and James Maxwell predicted that radio waves existed. In 1886 Heinrich Hertz conducted experiments which proved this to be the case and the first primitive radar system, in which radio waves were sent out and reflections from distant objects detected, was patented by German engineer Christian Hulsmeyer in 1904. Little was done to develop this use of radio waves until the late 1930’s when the threat of war led to at least eight countries – France, Germany, Italy, Japan, Netherlands, the Soviet Union, the United Kingdom, and the United States—independently developing radar. Britain’s air-defense radar system (known as Chain Home) was in place before the Second World War actually began as the government was aware of the very real threat from the German Luftwaffe, and during the next six years of conflict scientists and engineers found dozens of ways of using the simple and yet highly adaptable radar.

A committee set up by th British government in the 1930’s to consider the problem of air defence originally come up with the idea of using electromagnetic waves to develop a ‘death ray’, thankfully Robert Watson-Watt convinced them that this was a bad idea and to concentrate on an aircraft detection system instead! He recognised the importance of being able to see planes from a distance and follow their course in overcast weather or at night. Rapid progress was made as Watson-Watt used what he called his ‘third best principle’ – the best is usually unattainable and the second best unavailable until too late – this meant that they went with the ‘third best’ option and devised a system which worked with two antennas, one for transmitting and one for receiving, as they still had to develop a single antenna to do both. By 1939 a chain of eighteen radar stations was set up to cover the south and east coast of England. Chain Home, as it was called, used fixed transmitters to send out a broad beam of radio pulses to detect planes which were approaching at 1,500 – 2,000 feet; the stations were positioned on cliffs and high ground to give them a greater detection range and they could ‘see’ planes up to 200 miles away. The system was further developed in 1940 with the introduction of a new ground-based radar which could detect low-flying aircraft and ships. This was called Chain Home Low and differed from Chain Home by using a rotating aerial to transmit a narrow beam, rather like a searchlight. It could detect aircraft flying at 500ft from 110 miles away and display the information on a circular screen similar to modern radar displays. Stations could be set up on cliff tops, but if the coastal area they were protecting was low lying the transmitter and receiver would be mounted on towers 200 feet high.

Women in the WAAF worked in these radar centres. When a signal was received from approaching aircraft it was displayed on a green cathode ray tube. This showed the pulse sent out by the transmitter moving in from the edge of the screen with the target aircraft positioned in the centre. The screen could be calibrated for anything up to 200 miles which enabled the operator to ‘zoom in’ on the approaching craft. The radar operator would move a cursor over the position of the aircraft and the information was automatically sent to a calculating machine along with further information which enabled it to work out the plane’s height as well as position. This information was then sent to the mapping room with a large table on which the planes were positioned, a visual aid which made it easier for non-technical officers to direct the defending planes.

Chain Home was a massive step forward in air defence but it did have its problems. As the stations faced out to the sea contact was lost with enemy aircraft once they crossed the coastline, and Chain Home Low could not help either as it was difficult to distinguish between planes and signals from the ground. So the Observer Corps was given the job of watching the skies with tradition means (binoculars) and plotting enemy aircraft formations. Another problem was that although Chain Home picked up signals from approaching aircraft the signals could be misinterpreted and so inaccurate information about enemy strength and height could be passed to Air Command which meant that British fighter pilots could be put in dangerous situations, but the benefits far outweighed the drawbacks as the pilots no longer needed to conduct continuous air patrols.

The first serious use of radar came during the Battle of Britain when Chain Home was able to intercept approaching German bombers and fighters. It was even possible to ‘see’ the enemy at night with Air Interception (AI) (which allowed fighter planes to fly directly towards enemy bombers at night), Ground Control Interception (GCI) and the Plan Position Indicator (PPI), all thanks to radar; it was also possible for searchlights to use radar to help target planes for the anti-aircraft guns.

There were a number of other developments in the use of radar during the Second World War:

• Proximity fuse – a tiny radar set built into each artillery shell to trigger detonation when the shell was close to its target. By the end of the war 22 million had been produced and were particularly effective when used by anti-aircraft artillery.
• IFF – Identification Friend or Foe, which enabled Allied planes to identify each other using radar signals.
• H2S – an Air Interception system which could display a map of the ground below in an aircraft.
• Gee – a system of navigation which let bombers know their exact position at any time on their journey to Germany. Without Gee the 1,000-bomber raids would never have been possible.
• Oboe – a positioning system which allowed two bases back in England to pinpoint planes when they were directly over their target; Oboe made it possible for precision attacks on munitions factories in the Ruhr and on missile bases on the north coast of Europe.
• ASV – a Coastal Command aircraft carrying an ASV device could use it to pinpoint a U-boat on the surface; in conjunction with a similar device on destroyers and corvettes the Allies were finally able to defeat the German submarine menace which threatened to starve Britain into submission.

We often forget that Germany had its own effective radar systems on their bombers during the first months of the war. They also positioned their “Würzburg” system on the north coast of France to detect approaching aircraft. So why did radar seem to be much more successful for the Allies than the enemy? This can be put down, in part, to the attitude of those in positions of power with the Battle of Britain being a prime example. On 15^th August 1940, at the height of the Battle, Reichsmarschall Göering decided to halt attacks on Chain Home stations; his reasoning was that “It is doubtful whether there is any point in continuing attacks on radar sites, in view of the fact that not one of those attacked so far has been put out of action.” Unlike Göering, however, ACM Dowding recognised just how important radar was and what a benefit it would be if fully integrated into air strategy. The fact that the Germans stopped targeting the radar stations strengthened the British defence and played a critical role in the final victory of the Battle of Britain. As Sir William Douglas commented, “I think we can say that the Battle of Britain might never have been won… if it were not for the radar chain”.