After serious losses to the Luftwaffe during the daytime bombing of Great Britain, Hitler ordered the transition to the night war. This marked the beginning of a new phase in the air battle for Britain, which Churchill called "the war of the magicians." In particular, he noted the means that the British used to neutralize the radio navigation aids of German aircraft. Churchill wrote:
“It was a secret war, whose battles, whether victories or defeats, remained unknown to the public, and even now it is only faintly understood by those who do not belong to a narrow scientific circle of technical specialists. If British science weren't better than German science, and if these strange, sinister means were used in the battle for survival, we could almost certainly be defeated, crushed and destroyed."
Luftwaffe night bombers used to raid England
For a better understanding of how this secret war between Germany and Great Britain was prepared, it is necessary to go back several years and see how the Germans developed radio navigation systems. The first was the Lorenz company, which back in 1930 developed a system designed to land aircraft in poor visibility and at night. The novelty was named Lorenzbake. It was the first course glide system based on the principle of beam navigation. The main element of Lorenzbake was a radio transmitter operating at 33, 33 MHz and located at the end of the runway. The receiving equipment installed on the aircraft detected a ground signal at a distance of up to 30 km from the airfield. The principle was quite simple - if the plane was to the left of the GDP, then a number of Morse code dots could be heard in the pilot's headphones, and if to the right, then a series of dashes. As soon as the car was on the right course, a continuous signal sounded in the headphones. In addition, the Lorenzbake system provided for two radio beacon transmitters, which were installed at a distance of 300 and 3000 m from the start of the runway. They broadcast the signals vertically upward, which allowed the pilot, when flying over them, to estimate the distance to the airfield and start descending. Over time, visual indicators appeared on the dashboard of German aircraft, allowing the pilot to get rid of the constant listening to the radio broadcast. The system was so successful that it found application in civil aviation, and later spread to many European airports, including the UK. Lorenzbake began to be transferred to the military track in 1933, when the idea came to use radio navigation developments to increase the accuracy of night bombings.
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The principle of guidance of Luftwaffe bombers at Coventry
This is how the famous X-Gerate system was born, which consisted of several Lorenz emitters, of which one emitted the main radio navigation beam, and the others crossed it at certain points in front of the bombing point. The aircraft were even equipped with equipment for automatically dropping deadly cargo over the point of the airstrike. For the pre-war period, X-Gerate allowed aircraft to bombard the night with incredible precision. Already during the war, German bombers on their way to Coventry from Vonnes, France, crossed several radio navigation beams called Rhein, Oder and Elba. Their intersections with the main guide beam, named after the Weser River, were pre-mapped to the navigator, allowing accurate positioning over England at night. After 5 km of flight after crossing the last "checkpoint" Elbe, the German armada approached the target and automatically dropped its cargo on the center of the peacefully sleeping city. Recall that the British government knew about the course of this action in advance from Enigma's decryptions, but in order to preserve ultra-secrecy, it did not take any measures to save Coventry. Such accuracy of guidance of German bombers became possible after the occupation of France and Belgium by the Nazis, on whose coasts the emitters were placed. Their relative position allowed the navigation beams to be crossed over Britain at almost right angles, which increased accuracy.
The fact that Germany was intensively working on an electronic system based on radio beams was learned in Britain back in 1938, when a secret folder was handed over to the British naval attaché in Oslo. Sources claim that it was passed on by a "prudent scientist" who did not want to give Germany priority in such a perfect weaponry. In this folder, in addition to information about X-Gerate, there was information about the nature of work in Peenemünde, magnetic mines, jet bombs and a bunch of high-tech stuff. In Britain, at first, they were taken aback by such a stream of classified data and did not particularly trust the contents of the folder - there was a high probability that the Germans slipped misinformation. The point was put by Churchill, who said: "If these facts correspond to reality, then this is a mortal danger." As a result, a committee of scientists was created in Britain, who began to introduce the achievements of applied electronics into the military sphere. It is from this committee that all means of electronic suppression of German navigation will be born. But Hitler's scientists did not sit idly by either - they perfectly understood that the X-Gerate had a number of shortcomings. First of all, night bombers had to fly for a long time along the leading radio beam in a straight line, which inevitably led to frequent attacks by British fighters. In addition, the system was quite complicated for pilots and operators, which made them waste precious time on training bomber crews.
Radio intelligence Avro Anson
The British first encountered Germany's electronic radio navigation system on June 21, 1940, when the Avro Anson pilot, on a standard radio reconnaissance patrol, heard something new in his headphones. It was a sequence of very clear and distinct Morse code dots, behind which he soon heard a continuous beep. After a few tens of seconds, the pilot already heard the dash sequence. This is how the German bomber guidance radio beam on the cities of England was crossed. In response, British scientists have proposed a countermeasure based on the continuous emission of noise in the X-Gerate radio range. It is noteworthy that the medical apparatus for thermocoagulation, which were equipped with London hospitals, was perfectly suited for this unusual purpose. The device created electrical discharges that prevented enemy aircraft from receiving navigation signals. The second option was a microphone located near the rotating screw, which made it possible to broadcast such noise at X-Gerate frequencies (200-900 kHz). The most advanced system was Meacon, the transmitter and receiver of which were located in the south of England at a distance of 6 km from each other. The receiver was responsible for intercepting the signal from the X-Gerate, transmitting it to the transmitter, which immediately relayed it with a high signal amplification. As a result, the German planes caught two signals at once - one of their own, which was constantly weakening, and the second strong, but false. The automatic system, of course, was guided by a more powerful course beam, which led it in a completely different direction. Many German "bombers" dumped their cargo into an open field, and after using up the supply of kerosene, they were forced to land on British airfields.
Ju-88a-5, which the British landed at night with the entire crew at their airfield
Modern scale model of the Knickebein emitter
The response of the German military machine to such British tricks was the Knickebein (Crooked Leg) system, which got its name from the specific shape of the radiator antenna. The actual difference from Knickebein's X-Gerate was that only two transmitters were used, which only crossed at the bombing point. The advantage of the “crooked leg” was greater accuracy, since the sector of the continuous signal was only 3 degrees. X-Gerate and Knickebein were obviously used in parallel by the Germans for a long time.
Knickebein FuG-28a Signal Receiver
Bombing at night with Knickebein could be done with an error of no more than 1 km. But the British, through intelligence channels, as well as materials from a downed bomber, were able to quickly respond and created their own Aspirin. At the very beginning of the Knickebein system, specialized Avro Anson aircraft roamed the British sky in search of narrow beam from Knickebein and, as soon as they were recorded, relay stations entered the business. They selectively re-emitted a dot or dash at a higher power, which deviated the route of the bombers from the original and again took them to the fields. Also, the British learned to fix the point of intersection of the beams of the radio navigation system of the Germans and quickly raised fighters into the air to intercept. All this set of measures allowed the British to withstand the second part of the Luftwaffe operation, associated with the night bombing of England. But the electronic warfare did not end there, but only became more sophisticated.
