X procedure

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The X-procedure (code name "Wotan I") is the name of a German radio beacon system, which from 1934 under the direction of Johannes Plendl from the German Research Institute for Aviation (DVL), Rechlin branch - from 1936 part of the testing center of the Luftwaffe (E -stelle) - developed and introduced in 1938 after testing was completed. It was used at the beginning of the Second World War during the Battle of Britain for the guidance of Luftwaffe bombers . A square 300 meters wide could be hit at a distance of 350 km. The system used four beacons on frequenciesfrom 66 to 77 MHz ( wavelength : 4.5 to 3.9 meters).

Guide rays of the X-method (target)

It was based on a landing approach system (" Lorenzbake ") developed by the Berlin company C. Lorenz for civil air traffic from 1932, with which airports could be approached precisely when visibility was limited. This original method worked with a guide beam of 5 °, corresponding to 8 km width at 100 km distance, so too imprecise for attacks. Plendl improved the accuracy of this system by using higher frequencies around 70 MHz (compared to 30 to 38 MHz in the Lorenz Landing System), larger antennas with a smaller beam angle of 0.1 ° and significantly higher transmission powers . For this purpose, the transmitters "Berta I" (50 W) and "Berta II" (500 W) were developed at Telefunken . In contrast to the Lorenz landing system, the machines now flew away from the transmitter on the beacon ("Weser"). The beacon transmitter transmitted with two antennas, which were slightly inclined towards each other, so that two directional lobes resulted. The antenna radiating to the left sent Morse code ( Morse code "e"), the antenna radiating to the right Morse code (Morse code "t"). In the overlap area of ​​the signals the pilot heard a continuous tone and the machine was thus on the correct course. Initially, the signal had to be listened to through headphones, but a later version converted it and displayed the deviation on an instrument.

In front of the target, three signal beams crossed the beacon. From the first signal about 30 km beforehand ("Rhine"), the pilot had to keep exactly the center of the beacon and the speed. The bombardier now waited for the second signal around 10 km from the target (“Oder”), at which he had to start a special “X-clock”. He had to press this again when he crossed the third signal 5 km before the destination ("Elbe"). This determined the speed over the ground and the watch automatically triggered the bombing after a certain period of time, which, depending on the speed, was less than a minute.

The target area could be reached with high accuracy with the X-procedure, 50% of the bombs landed after a flight distance of 300 km in a target circle of ± 300 m. After the end of the trial in 1937, 100 on-board radios and 20 ground stations were ordered. These few devices were concentrated in special Combat Group 100 bombers . This “ boy scout ” concept was copied and perfected only a few years later by the RAF .

At that time, the German Air Force was the only one in the world that could fly a precision attack at night or in poor visibility. At the same time, the British Royal Air Force (RAF) was still working with an astronomical navigation method as in seafaring.

X systems were used in the initial phase of the German offensive during night attacks, including at the company Mondscheinsonate on 14/15. November 1940 against Coventry . For the night air raids on England, two X-transmitting stations were initially aimed at a city to be bombed, and more were added later. Sending stations have been set up at the following locations (selection):

The X procedure was deciphered in England, mainly by Reginald Victor Jones , and was successfully disrupted as early as 1940 by radio stations transmitting the point Morse signal, which led to irritation and, as a result, to trajectories outside the actual beacon. However, these “Domino” jammers were accidentally set to the wrong frequency before the major attack on Coventry.

After the war, the inventor on the German side, Johannes Plendl , and the defender on the British side, Reginald Victor Jones , got together and became good friends.

See also

literature

  • B. Johnson: Top Secret - Science and Technology in World War II. Weltbild-Verlag, Augsburg 1999, ISBN 389350818X .
  • RV Jones: Most Secret War: British Scientific Intelligence 1939-1945. First published 1978 Hamish Hamilton. Coronet paperback edition 1979 ISBN 0-340-24169-1 .
  • Fritz Trenkle : The German radio control procedures until 1945. Dr. Alfred Hüthig, Heidelberg 1987, ISBN 3-7785-1647-7 .
  • Joachim Beckh: Lightning and Anchor. Volume 2: Information technology, history & background. ISBN 3833429976 .

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