Battle of the Beams

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The Battle of the Beams was a period early in WW2 when bombers of the German Air Force (Luftwaffe) used a number of increasingly accurate systems of radio navigation for night bombing in the United Kingdom. British scientific intelligence at the Air Ministry fought back with a variety of their own increasingly effective means, involving jamming and distortion of the radio waves. The period ended when the Wehrmacht moved their forces to the East in May 1941, in preparation for the attack on the Soviet Union.

Prior to the war, Lufthansa and the German aircraft industry invested heavily in the development of commercial aviation, and systems and methods that would improve safety and reliability. Considerable effort went into blind landing aids which allowed aircraft to approach an airport at night or in bad weather. The primary system developed for this role was the Lorenz system, developed by Johannes Plendl, which was in the process of being widely deployed on large civilian and military aircraft.

In WW2, the Lorenz beam principle was used by the German Luftwaffe as the basis of a number of blind bombing aids, notably Knickebein ('crooked leg') and the X-Gerät ('X-Apparatus'), in their bombing offensive against English cities during the winter of 1940/41. Knickebein was very similar to LFF, modifying it only slightly to be more highly directional and work over much longer distance. Using the same frequencies allowed their bombers to use the already-installed LFF receivers, although a second receiver was needed in order to pinpoint a single location.

The X-Gerät involved cross-beams of the same characteristics but on different frequencies, which would both enable the pilot to calculate his speed (from the elapsed time between crossing the Fore Cross Signal and crossing the Main Cross Signal), and indicate when he should drop his payload. The calculation was performed by a mechanical computer. Lorenz modified this system to create the Viktoria/Hawaii lateral guidance system for the V-2 rocket.

When the British discovered the existence of the 'Knickebein' system, they rapidly jammed it, however, the 'X-Gerät' was not successfully jammed until later. A later innovation by the Germans was the 'Baedeker' or 'Taub' modification, which used supersonic modulation. This was so quickly jammed that the Germans practically gave up on the use of beam-bombing systems, with the exception of the 'FuGe 25A', which operated for a short time towards the end of Operation Steinbock, known as the "Baby Blitz".

A further operational drawback of the system was that bombers had to follow a fixed course between the beam transmitter station and the target; once the beam had been detected, defensive measures were made more effective by knowledge of the course.

https://en.wikipedia.org/wiki/Battle_of_the_Beams .

https://en.wikipedia.org/wiki/Lorenz_beam .