Battle Stations II
Radar
'Radar' is an acronym for 'radio direction and ranging', coined by the Americans in 1942. Previously, the system had been known by a variety of names: in Britain, it was 'RDF' (radio direction finding); in Germany, 'DT'; and in the United States, 'Derax'.
The principle by which radar works is really quite simple. A pulse of radio energy is sent out towards a target. When it strikes this, some of the energy that is reflected back can be detected. The speed of the pulse is known, and the time between sending it and receiving the reflected energy can be measured. As a result, the distance to the target – the range – can be accurately determined.
The mechanism behind radar was discovered and developed independently in Britain, the United States, France and Germany in the mid-1930s. Differing strategic requirements meant that the pace and direction of radar development in these countries varied markedly.
The British fear of devastating bombing attacks in any future war added urgency to their development of this new technology. In 1934, the Air Ministry asked Robert Watson-Watt to examine the feasibility of developing a 'death ray' using ultra-high-frequency radiation. This impractical request led to the detection of aircraft at long range via a cathode ray tube (CRT) display, which made it possible to plot position, altitude and course. By fitting friendly aircraft with a discrete pulse repeater, it was also possible for an operator to identify friend and foe (IFF). The first successful radar experiment in Britain was made in February 1935.
In contrast, the Germans concentrated on using radar to provide accurate gunfire control for warships. The French treated it as a navigational aid. And while the Americans realised radar's value as an early-warning device, they gave it a low priority.
On the outbreak of war in September 1939, only Britain had a practical radar defensive system. The 'Chain Home' network of radar stations was established along the coastline from Land's End in the south-west to Newcastle upon Tyne in the north-east.
These two stations represented the extremities of an integrated system that fed information – bearings, height, numbers of aircraft – back to RAF Fighter Command headquarters at Bentley Priory. After this data was cross-checked, orders were issued to the relevant group and sector fighter stations to scramble aircraft to meet the incoming threat. Without radar, victory in the Battle of Britain in 1940 would have been impossible.
The demands of war accelerated the creation of new applications of radar technology. The RAF's night fighters were fitted with airborne radar, as were the Luftwaffe's equivalents as RAF Bomber Command's strategic bombing campaign against Germany gathered pace. From late 1941, Bomber Command used an increasingly sophisticated array of active and passive radar to find their targets at night. The radar control of anti-aircraft guns was also introduced by both sides, although the Germany technology was hampered by Hitler's insistence on promoting only offensive weapon design.
From 1941, ship and airborne radar also became a crucial Allied weapon against German U-boats in the Battle of the Atlantic, particularly after centimetric radar, with its greater resistance to jamming, replaced lower wavelength sets. The key to centimetric radar was the cavity magnetron, developed by the British in 1940.
This, in turn, gave impetus to the US radar programme. It was an important factor in the victory achieved in the Pacific, a theatre dominated by long-range air, surface and submarine naval warfare. The Japanese had not developed a radar capability.
