The Battle of the Beams was a period early in the
Second World War
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
when bombers of the German Air Force (''
Luftwaffe
The ''Luftwaffe'' () was the aerial-warfare branch of the German ''Wehrmacht'' before and during World War II. Germany's military air arms during World War I, the ''Luftstreitkräfte'' of the Imperial Army and the '' Marine-Fliegerabtei ...
'') used a number of increasingly accurate systems of
radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination.
The basic principles a ...
for night bombing in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
. British scientific intelligence at the
Air Ministry
The Air Ministry was a department of the Government of the United Kingdom with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964. It was under the political authority of the Secretary of State ...
fought back with a variety of their own increasingly effective means, involving
jamming and deception signals. The period ended when the
Wehrmacht
The ''Wehrmacht'' (, ) were the unified armed forces of Nazi Germany from 1935 to 1945. It consisted of the ''Heer'' (army), the ''Kriegsmarine'' (navy) and the ''Luftwaffe'' (air force). The designation "''Wehrmacht''" replaced the previous ...
moved their forces to the East in May 1941, in preparation for the
attack on the Soviet Union.
The idea of "beam" based navigation was developed during the 1930s, initially as a
blind landing
Blind may refer to:
* The state of blindness, being unable to see
* A window blind, a covering for a window
Blind may also refer to:
Arts, entertainment, and media Films
* ''Blind'' (2007 film), a Dutch drama by Tamar van den Dop
* ''Blind' ...
aid. The basic concept is to produce two directional radio signals that are aimed slightly to the left and right of a
runway
According to the International Civil Aviation Organization (ICAO), a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a man-made surface (often asphalt concrete, as ...
's midline. Radio operators in the aircraft listen for these signals and determine which of the two beams they are flying in. This is normally accomplished by sending
Morse code
Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one of ...
signals into the two beams, to identify right and left.
For bombing, the ''Luftwaffe'' built huge versions of the antennas to provide much greater accuracy at long range, named ''Knickebein'' and ''X-Gerät''. These were used during the early stages of "
The Blitz
The Blitz was a German bombing campaign against the United Kingdom in 1940 and 1941, during the Second World War. The term was first used by the British press and originated from the term , the German word meaning 'lightning war'.
The Germa ...
" with great effect, in one case laying a strip of bombs down the centerline of a factory deep in England. Tipped off about the system's operation by pre-war
military intelligence
Military intelligence is a military discipline that uses information collection and analysis approaches to provide guidance and direction to assist commanders in their decisions. This aim is achieved by providing an assessment of data from a ...
, the British responded by sending their own Morse code signals so that the aircraft believed they were always properly centred in the beam while they flew wildly off course. The Germans became convinced the British had somehow learned to bend radio signals.
When the problem became widespread, the Germans introduced a new system that worked on different principles, the ''Y-Gerät''. Having guessed the nature of this system from a passing mention, the British had already deployed countermeasures that rendered the system useless almost as soon as it was used. The Germans eventually abandoned the entire concept of radio navigation over the UK, concluding the British would continue to successfully jam it.
Background
![Lorenz beam](https://upload.wikimedia.org/wikipedia/commons/8/87/Lorenz_beam.svg)
Before the start of the war in 1939,
''Lufthansa'' and the German aircraft industry invested heavily in the development of commercial aviation, and in systems and methods that would improve safety and reliability. Considerable effort went into
blind-landing
In aviation, an instrument approach or instrument approach procedure (IAP) is a series of predetermined maneuvers for the orderly transfer of an aircraft operating under instrument flight rules from the beginning of the initial approach to a landi ...
aids which allowed aircraft to approach an airport at night or in foul weather. The primary system developed for this was the
Lorenz system
The Lorenz system is a system of ordinary differential equations first studied by mathematician and meteorologist Edward Lorenz. It is notable for having chaotic solutions for certain parameter values and initial conditions. In particular, the Lo ...
, developed by
Johannes Plendl
Johannes "Hans" Plendl (6 December 1900 – 10 May 1991), German radar pioneer, was the scientist whose airplane navigation inventions made possible the early German bombing successes in World War II.
Early life
Plendl was born in 1900 in Munich, ...
, which was in the process of being widely deployed on large civilian and military aircraft.
The Lorenz system worked by feeding a special three-element antenna system with a
modulated
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...
radio signal. The signal was fed to the centre
dipole
In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways:
*An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system i ...
, which had a slightly longer
reflector element on either side set slightly back. A switch rapidly alternated the opened midpoint connection of each reflector in turn, sending the beam slightly to the left and then slightly to the right of the centreline of the runway. The beams widened as they spread from the antennas, so there was an area directly off the runway approach where the two signals overlapped. The switch was timed so it spent longer on the right side of the antenna than the left.
An aircraft approaching the airport would tune one of their radios to the Lorenz frequency. If the crew was on the left side of the centreline, they would hear a series of short tones followed by long pauses, meaning the aircraft was on the "dot" side of the antenna. Hearing the "dots", they would know that they had to veer to the right to fly down the centreline. If the crew was on the right side of the centerline, they would hear a series of long tones followed by short pauses, meaning the aircraft was on the "dash" side of the antenna. Hearing the "dashes", they would know that they had to veer to the left to fly down the centreline. In the centre, the radio would receive both signals, where the dots filled in the gaps in the dashes and produced a continual signal, the so-called "equisignal". Flying in the known direction of the runway and keeping the equisignal on the radio, Lorenz-equipped crews could guide an aircraft down a straight line with a relatively high degree of accuracy, so much so that pilots could then find the runway visually except in the worst conditions.
Night bombing
During the early 1930s, the concept of a
night bombing
A night bomber is a bomber aircraft intended specifically for carrying out bombing missions at night. The term is now mostly of historical significance. Night bombing began in World War I and was widespread during World War II. A number of moder ...
strategic campaign began to become paramount in military aviation circles. This was due to the ever-increasing performance of
bombers
A bomber is a military combat aircraft designed to attack ground and naval targets by dropping air-to-ground weaponry (such as bombs), launching torpedoes, or deploying air-launched cruise missiles. The first use of bombs dropped from an aircraf ...
, which were beginning to have the capability to strike across Europe with useful bomb loads. These aircraft were slow and lumbering, easy prey for
interceptors
An interceptor aircraft, or simply interceptor, is a type of fighter aircraft designed specifically for the defensive interception role against an attacking enemy aircraft, particularly bombers and reconnaissance aircraft. Aircraft that are c ...
, but this threat could be essentially eliminated by flying at night. A bomber, painted black, could be spotted only at very short ranges. As the bomber's altitude and speed increased, the threat from ground-based defences was greatly reduced. Planners believed that "
the bomber will always get through
"The bomber will always get through" was a phrase used by Stanley Baldwin in a 1932 speech "A Fear for the Future" given to the British Parliament. His speech stated that contemporary bomber aircraft had the performance necessary to conduct a s ...
".
The problem with night bombing is that the same limitations in visibility meant the bomb crew would have a difficult time finding their targets, especially a
blacked-out target at night. Only the largest targets, cities, could be attacked with any probability of success.
To support this mission, the RAF invested heavily in navigation training, equipping their aircraft with various devices, including an
astrodome
The NRG Astrodome, also known as the Houston Astrodome or simply the Astrodome, is the world's first multi-purpose, domed sports stadium, located in Houston, Texas. It was financed and assisted in development by Roy Hofheinz, mayor of Houston ...
for taking a
star fix and giving the navigator room to do his calculations in an illuminated workspace. This system was put to use as soon as the war began and was initially regarded as successful. In reality, the early bombing effort was a complete failure, with the majority of bombs landing miles from their intended targets.
The Luftwaffe did not take such a fatalistic view of air warfare, and continued to research accurate night bombing against smaller targets. Not depending on celestial navigation, they invested their efforts in
radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination.
The basic principles a ...
systems. The Luftwaffe concentrated on developing a bombing direction system based on the Lorenz concept through the 1930s, as it made night navigation relatively easy by simply listening for signals on a radio set, and the necessary radios were already being installed on many aircraft.
Lorenz had a range of about , enough for blind-landing but not good enough for bombing raids over the UK. This could be addressed by using more powerful transmitters and highly sensitive receivers. In addition the Lorenz beams were deliberately set wide enough that they could be easily picked up at some distance from the runway centreline, but this meant their accuracy at long ranges was fairly limited. This was not a problem for
blind landing
Blind may refer to:
* The state of blindness, being unable to see
* A window blind, a covering for a window
Blind may also refer to:
Arts, entertainment, and media Films
* ''Blind'' (2007 film), a Dutch drama by Tamar van den Dop
* ''Blind' ...
, where the distance covered by the fan-shaped beams decreased as the aircraft approached the transmitters, but for use in the bombing role this would be reversed, and the system would have maximum inaccuracy over the target.
German systems
''Knickebein''
![Map of Knickebein transmitters](https://upload.wikimedia.org/wikipedia/commons/9/93/Map_of_Knickebein_transmitters.svg)
For bombing use, the modifications to Lorenz were fairly minor. Much larger antennas were needed to provide the required accuracy. This was achieved by using aerials with many more elements, but it retained the simple switching of two of the reflector elements to alter the beam directions very marginally. The beam angles were so dramatically reduced that it was only a few tens of yards wide over the target. It was the shape of the aerials that gave the system its code name, ''Knickebein'', which means "crooked leg", although the word is also the name of a magical raven in
Germanic mythology
Germanic mythology consists of the body of myths native to the Germanic peoples, including Norse mythology, Anglo-Saxon mythology, and Continental Germanic mythology. It was a key element of Germanic paganism.
Origins
As the Germanic language ...
. For the required range, transmitted power was increased considerably. The ''Knickebein'' receivers were disguised as a standard blind landing receiver system, consisting apparently of the EBL-1 and the EBL-2 receivers.
The beam from a single transmitter would guide the bombers towards the target, but could not tell them when they were over it. To add this ranging feature, a second transmitter similar to the first was set up so its beam crossed the guidance beam at the point where the bombs should be dropped. The aerials could be rotated to make the beams from two transmitters cross over the target. The bombers would fly into the beam of one and ride it until they started hearing the tones from the other (on a second receiver). When the steady "on course" sound was heard from the second beam, they dropped their bombs.
![Knickebein antenna](https://upload.wikimedia.org/wikipedia/commons/4/41/Knickebein_antenna.svg)
The first of these new ''Knickebein'' transmitters was set up in 1939 on
Stollberg hill in
Nordfriesland
Nordfriesland (; da, Nordfrisland; frr, Nordfraschlönj ), also known as North Frisia, is the northernmost district of Germany, part of the state of Schleswig-Holstein. It includes almost all of traditional North Frisia (with the exception o ...
near the border with
Denmark
)
, song = ( en, "King Christian stood by the lofty mast")
, song_type = National and royal anthem
, image_map = EU-Denmark.svg
, map_caption =
, subdivision_type = Sovereign state
, subdivision_name = Danish Realm, Kingdom of Denmark
...
; at
Kleve (Cleves) near the Dutch border, almost the most westerly point in Germany, and at
Lörrach
Lörrach () is a town in southwest Germany, in the valley of the Wiese, close to the French and the Swiss borders. It is the capital of the district of Lörrach in Baden-Württemberg. It is the home of a number of large employers, including the ...
near the border with France and Switzerland in south-western Germany. Following the fall of France in June 1940, additional transmitters were installed on the French coast. Stations were also constructed in Norway and the Netherlands.
Knickebein was used in the early stages of the German night-bombing offensive and proved to be fairly effective, but the tactics for using the system in a widespread bombing effort were not yet developed, so much of the early German night bombing offensive was limited to area bombing.
The search for the beams
Efforts in Britain to block the ''Knickebein'' system required time to implement. British intelligence at the Air Ministry, led by
R. V. Jones
Reginald Victor Jones , FRSE, LLD (29 September 1911 – 17 December 1997) was a British physicist and scientific military intelligence expert who played an important role in the defence of Britain in by solving scientific and technical p ...
, became aware of the system when the
Royal Aircraft Establishment
The Royal Aircraft Establishment (RAE) was a British research establishment, known by several different names during its history, that eventually came under the aegis of the Ministry of Defence (United Kingdom), UK Ministry of Defence (MoD), bef ...
analysed a downed German bomber's Lorenz system and observed it was far more sensitive than required for a mere landing aid. Secretly recorded transcripts from German prisoner of war pilots indicated this may have been a bomb aiming aid.
Winston Churchill
Sir Winston Leonard Spencer Churchill (30 November 187424 January 1965) was a British statesman, soldier, and writer who served as Prime Minister of the United Kingdom twice, from 1940 to 1945 Winston Churchill in the Second World War, dur ...
had also been given
Ultra
adopted by British military intelligence in June 1941 for wartime signals intelligence obtained by breaking high-level encrypted enemy radio and teleprinter communications at the Government Code and Cypher School (GC&CS) at Bletchley Park. '' ...
intelligence from decrypted
Enigma
Enigma may refer to:
*Riddle, someone or something that is mysterious or puzzling
Biology
*ENIGMA, a class of gene in the LIM domain
Computing and technology
* Enigma (company), a New York-based data-technology startup
* Enigma machine, a family ...
messages that mentioned 'bombing beams'.
When Jones mentioned the possibility of bombing beams to Churchill, he ordered further investigation. The British codenamed the system Headache. Many in the Air Ministry did not believe that the system was in use.
Frederick Lindemann
Frederick Alexander Lindemann, 1st Viscount Cherwell, ( ; 5 April 18863 July 1957) was a British physicist who was prime scientific adviser to Winston Churchill in World War II.
Lindemann was a brilliant intellectual, who cut through bureauc ...
, leading scientific adviser to the government, argued that any such system would not be able to follow the curvature of the Earth, although
T. S. Eckersley of the Marconi company had said it could.
Eckersley's assertion was eventually demonstrated after Churchill ordered a flight to try to detect the beams. The RAF lacked equipment capable of detecting 30–33 MHz Lorenz signals, so they purchased an American
Hallicrafters
The Hallicrafters Company manufactured, marketed, and sold radio equipment, and to a lesser extent televisions and phonographs, beginning in 1932. The company was founded by William J. Halligan and based in Chicago, Illinois, United States.
In ...
S-27
amateur radio
Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communic ...
receiver from a shop in Lisle Street, London. The receiver was fitted into an
Avro Anson
The Avro Anson is a British twin-engined, multi-role aircraft built by the aircraft manufacturer Avro. Large numbers of the type served in a variety of roles for the Royal Air Force (RAF), Fleet Air Arm (FAA), Royal Canadian Air Force (RCAF) a ...
and operated by a member of the
Y Service
The "Y" service was a network of British signals intelligence collection sites, the Y-stations. The service was established during the First World War and used again during the Second World War. The sites were operated by a range of agencies inc ...
. The flight was nearly cancelled when Eckersley withdrew his assertion that the beams would bend round the earth. Jones saved the flight by pointing out that Churchill himself had ordered it, and he would make sure that the Prime Minister would learn who cancelled it.
The crew were not told specifics, and were simply ordered to search for radio signals around 30 MHz having Lorenz characteristics and, if they found any, to determine their bearing. The flight took off and eventually flew into the beam from Kleve, on 31.5 MHz. It subsequently located the cross beam from Stollberg (its origin was unknown prior to this flight). The radio operator and navigator were able to plot the path of the beams and discovered that they intersected above the
Rolls-Royce
Rolls-Royce (always hyphenated) may refer to:
* Rolls-Royce Limited, a British manufacturer of cars and later aero engines, founded in 1906, now defunct
Automobiles
* Rolls-Royce Motor Cars, the current car manufacturing company incorporated in ...
engine factory at
Derby
Derby ( ) is a city and unitary authority area in Derbyshire, England. It lies on the banks of the River Derwent in the south of Derbyshire, which is in the East Midlands Region. It was traditionally the county town of Derbyshire. Derby gai ...
, at that time the only factory producing the
Merlin
Merlin ( cy, Myrddin, kw, Marzhin, br, Merzhin) is a mythical figure prominently featured in the legend of King Arthur and best known as a mage, with several other main roles. His usual depiction, based on an amalgamation of historic and le ...
engine. It was subsequently realised that the argument over whether the beams would bend round the earth was entirely academic, as the transmitters were more or less in line-of-sight to high altitude bombers.
British sceptics started regarding the system as proof that the German pilots were not as good as their own, who they believed could do without such systems. The
Butt Report
The Butt Report, released on 18 August 1941, was a report prepared during World War II, revealing the widespread failure of RAF Bomber Command aircraft to hit their targets.
At the start of the war, Bomber Command had no real means of determini ...
proved this to be wrong;
aerial reconnaissance
Aerial reconnaissance is reconnaissance for a military or strategic purpose that is conducted using reconnaissance aircraft. The role of reconnaissance can fulfil a variety of requirements including artillery spotting, the collection of ima ...
returned photographs of the RAF bombing raids, showing that they were rarely, if ever, anywhere near their targets.
Countermeasure
Efforts to block the ''Knickebein'' headache were codenamed "Aspirin". Initially, modified medical
diathermy
Diathermy is electrically induced heat or the use of high-frequency electromagnetic currents as a form of physical therapy and in surgical procedures. The earliest observations on the reactions of high-frequency electromagnetic currents upon the ...
sets transmitted interference. Later, local radio transmitters broadcast an extra "dot signal" at low power on nights where raids were expected. The German practice of turning on the beams long before the bombers reached the target area aided the British efforts. Avro Ansons fitted with receivers would be flown around the country in an attempt to capture the beams' location; a successful capture would then be reported to nearby broadcasters.
The low-power "dot signal" was initially transmitted essentially at random, so German navigators would hear two dots. This meant there were many equi-signal areas, and no easy way to distinguish them except by comparing them with a known location. The British transmitters were later modified to send their dots at the same time as the German transmitters, making it impossible to tell which signal was which. In this case the navigators would receive the equi-signal over a wide area, and navigation along the bombline became impossible, with the aircraft drifting into the "dash area" and no way to correct for it.
Thus the beam was seemingly "bent" away from the target. Eventually, the beams could be inclined by a controlled amount which enabled the British to fool the Germans into dropping their bombs where they wanted them. A side effect was that as the German crews had been trained to navigate solely by the beams, many crews failed to find either the true equi-signal or Germany again. Some Luftwaffe bombers even landed at RAF bases, believing they were back in the ''Reich''.
''X-Gerät''
![X-Gerät v3](https://upload.wikimedia.org/wikipedia/commons/b/b1/X-Ger%C3%A4t_v3.svg)
As good as ''Knickebein'' was, it was never intended to be used in the long-range role. Plendl had been working for some time to produce a much more accurate version of the same basic concept, which was eventually delivered as ''X-Gerät'' (X-Apparatus). ''X-Gerät'' used a series of beams to locate the target, each beam named after a river. The main beam, ''Weser'', was similar in concept to the one used in ''Knickebein'' but operated at a much higher frequency. Due to the nature of radio propagation, this allowed its two beams to be pointed much more accurately than ''Knickebein'' from a similarly sized antenna; the equi-signal area was only about wide at a distance of from the antenna. The beams were so narrow that bombers could not find them without help, so a low-power wide-beam version of ''Knickebein'' was set up at the same station to act as a guide. The main ''Weser'' antenna was set up just to the west of
Cherbourg
Cherbourg (; , , ), nrf, Chèrbourg, ) is a former commune and subprefecture located at the northern end of the Cotentin peninsula in the northwestern French department of Manche. It was merged into the commune of Cherbourg-Octeville on 28 Feb ...
in France.
The "cross" signal in ''X-Gerät'' used a series of three very narrow single beams, ''Rhine'', ''Oder'' and ''Elbe''. They were carefully aimed to define a precise bomb release trajectory. First a bomb release point along ''Weser'' was determined, by calculating the ''range'' or distance the bombs would travel between release and impact, and picking a point at that range to target. The ''Elbe'' beam intersected ''Weser'' before the release point. The ''Oder'' beam intersected ''Weser'' before the release point, or before ''Elbe''. ''Rhine'' did not require the same precision and was approximately before the release point. The beams' width added a small error to the intersection coordinates, on the order of tens to hundreds of meters.
As the bomber followed the ''Weser'' beam and reached ''Rhine'', the radio operator heard a brief signal and set up his equipment. This consisted of a special stop-clock with two hands. When the ''Oder'' signal was received the clock automatically started and the two hands simultaneously swept up from zero. When the ''Elbe'' signal was received, one hand stopped and the other reversed, sweeping back towards zero. The stopped hand indicated an accurate measurement of travel time from ''Oder'' to ''Elbe''. Since the ''Oder'' to ''Elbe'' distance equalled the ''Elbe'' to release point distance, a bomber flying at constant speed arrived at the release point as the moving hand reached zero, when the bombs were automatically released.
''X-Gerät'' operated at a much higher frequency than ''Knickebein'' (around 60 MHz) and thus required the use of new radio equipment. There was not enough equipment to fit all bombers, so the experimental unit
''Kampfgruppe'' 100 (''KGr'' 100) was given the task of using their ''X-Gerät'' equipment to guide other aircraft to the target. To do this, ''KGr'' 100 aircraft would attack as a small group first, dropping flares which other aircraft would then see and bomb visually. This is the first use of the
pathfinder
Pathfinder may refer to:
Businesses
* Pathfinder Energy Services, a division of Smith International
* Pathfinder Press, a publisher of socialist literature
Computing and information science
* Path Finder, a Macintosh file browser
* Pathfinder ( ...
concept that the RAF improved to great effect against the Germans some three years later.
The system was first tested on 20 December 1939 when a bomber from KGr 100 flown by
Oberleutnant
() is the highest lieutenant officer rank in the German-speaking armed forces of Germany (Bundeswehr), the Austrian Armed Forces, and the Swiss Armed Forces.
Austria
Germany
In the German Army, it dates from the early 19th century. Trans ...
Hermann Schmidt flew over London at 7,000m (23,000 ft).
[Hooton 1999, p. 199.]
''X-Gerät'' was used effectively in a series of raids known to the Germans as Moonlight Sonata, against
Coventry
Coventry ( or ) is a City status in the United Kingdom, city in the West Midlands (county), West Midlands, England. It is on the River Sherbourne. Coventry has been a large settlement for centuries, although it was not founded and given its ...
,
Wolverhampton
Wolverhampton () is a city, metropolitan borough and administrative centre in the West Midlands, England. The population size has increased by 5.7%, from around 249,500 in 2011 to 263,700 in 2021. People from the city are called "Wulfrunian ...
and
Birmingham
Birmingham ( ) is a city and metropolitan borough in the metropolitan county of West Midlands in England. It is the second-largest city in the United Kingdom with a population of 1.145 million in the city proper, 2.92 million in the West ...
. In the raid on Birmingham only ''KGr'' 100 was used and British post-raid analysis showed that the vast majority of the bombs dropped were placed within of the mid-line of the ''Weser'' beam, spread along it for a few hundred yards. This was the sort of accuracy that even daytime bombing could rarely achieve. The
raid on Coventry with full support from other units dropping on their flares almost destroyed the city centre.
Countermeasure
''X-Gerät'' proved more difficult to stop than ''Knickebein''. Initial defences against the system were deployed in a similar fashion to ''Knickebein'' in an attempt to disrupt the Coventry raid but proved to be a failure. Although Jones had correctly guessed the beam layout (and acknowledges it was only a guess), the modulation frequency had been measured incorrectly as 1,500 Hz, but was in fact 2,000 Hz. At the time it was believed that this would not make any difference, as the tones were close enough that an operator would have a hard time distinguishing them in a noisy aircraft.
The mystery was eventually revealed after an ''X-Gerät''-equipped
Heinkel He 111
The Heinkel He 111 is a German airliner and bomber designed by Siegfried and Walter Günter at Heinkel Flugzeugwerke in 1934. Through development, it was described as a "wolf in sheep's clothing". Due to restrictions placed on Germany after th ...
crashed on 6 November 1940 on the English coast at
West Bay, Bridport. Although the aircraft sank during the recovery operation, the waterlogged ''X-Gerät'' equipment was recovered. On examination, it was learned that a new instrument was being used that automatically decoded the dots and dashes and moved a pointer on a display in the cockpit in front of the pilot. This device was fitted with a very sharp filter which was sensitive only at 2,000 Hz, and not to the early British 1,500 Hz counter-signals. While the jammers were modified accordingly, this came too late for the raid on Coventry on 14 November; but the modified jammers were able to successfully disrupt a raid on Birmingham on 19 November.
''X-Gerät'' was eventually defeated in another manner, by way of a "false ''Elbe''" which was set up to cross the 'Weser' guide beam at a mere after the ''Oder'' beam — much earlier than the expected . Since the final stages of the release were automatic, the clock would reverse prematurely and drop the bombs kilometres short of the target. Setting up this false beam proved very difficult as the Germans, learning from their mistakes with ''Knickebein'', did not switch the ''X-Gerät'' beams on until as late as possible, making it much more difficult to arrange the "false ''Elbe''" in time.
''Y-Gerät''
As the British slowly gained the upper hand in the Battle of the Beams, they started considering what the next German system would entail. Since Germany's current approaches had been rendered useless, an entirely new system would have to be developed. Jones believed that if they could defeat this system quickly, the Germans might give up on the entire concept.
British monitors soon started receiving intelligence from
Enigma decrypts referring to a new device known as ''Y-Gerät'', which was also sometimes referred to as ''Wotan''. Jones had already concluded the Germans used code names that were too descriptive, so he asked a specialist in the German language and literature at
Bletchley Park
Bletchley Park is an English country house and estate in Bletchley, Milton Keynes ( Buckinghamshire) that became the principal centre of Allied code-breaking during the Second World War. The mansion was constructed during the years following ...
about the word ''Wotan''. The specialist realised ''Wotan'' referred to
Wōden
Odin (; from non, Óðinn, ) is a widely revered god in Germanic paganism. Norse mythology, the source of most surviving information about him, associates him with wisdom, healing, death, royalty, the gallows, knowledge, war, battle, victory, ...
, a one-eyed god, and might refer to a single-beam navigation system. Jones agreed, and knew that a system with one beam would have to include a distance-measurement system. He concluded that it might work on the basis described by the anti-Nazi German mathematician and physicist
Hans Mayer
Hans Mayer (19 March 1907 in Cologne – 19 May 2001 in Tübingen; pseudonym: ''Martin Seiler'') was a German literary scholar. Mayer was also a jurist and social researcher and was internationally recognized as a critic, author and musicologist ...
, who while visiting Norway had provided a large amount of information in what is now known as the
Oslo Report The Oslo Report was one of the most spectacular leaks in the history of military intelligence. Written by German mathematician and physicist Hans Ferdinand Mayer on 1 and 2 November 1939 during a business trip to Oslo, Norway, it described several G ...
.
''Y-Gerät'' used a single narrow beam pointed over the target, similar to earlier beam systems, transmitting a modulated radio signal. The system used a transponder (
FuG 28a) that received the signal from the beam and immediately re-transmitted it to the ground station. The ground station listened for the return signal and compared the phase of its modulation to the transmitted signal, which accurately determined the transit time of the signal, and hence the distance to the aircraft. Coupled with the direction of the beam (adjusted for a maximum return signal), the bomber's position could be established with considerable accuracy. The bombers did not have to track the beam, instead the ground controllers could calculate it and then give radio instructions to the pilot to correct the flight path.
Jones later learned that his guess on the operating principle based on the name Wotan was entirely by luck. Later documents showed that the original X-Gerät was known as Wotan I, and the Y-Gerät as Wotan II. Had he known the name was also associated with X-Gerät it was unlikely he would have concluded the system used a single beam.
Countermeasure
![AlexandraPalace](https://upload.wikimedia.org/wikipedia/commons/3/38/AlexandraPalace.jpg)
The British were ready for this system even before it was used. By chance, the Germans had chosen the operating frequency of the ''Wotan'' system badly. It operated at 45 MHz, which happened to be the frequency of the powerful-but-dormant
BBC #REDIRECT BBC #REDIRECT BBC #REDIRECT BBC
Here i going to introduce about the best teacher of my life b BALAJI sir. He is the precious gift that I got befor 2yrs . How has helped and thought all the concept and made my success in the 10th board ex ...
television transmitter at
Alexandra Palace
Alexandra Palace is a Grade II listed entertainment and sports venue in London, situated between Wood Green and Muswell Hill in the London Borough of Haringey. It is built on the site of Tottenham Wood and the later Tottenham Wood Farm. Origi ...
. All Jones had to do was arrange for the return signal to be received from the aircraft and then sent to Alexandra Palace for re-transmission. The combination of the two signals modified the phase shift, and thus the apparent transit delay. Initially, the signal was re-transmitted at low power, not powerful enough for the Germans to realise what was happening, but enough to spoil the accuracy of the system. Over subsequent nights, the transmitter power was gradually increased.
As ''Y-Gerät''s use went on, the aircrew accused the ground station of sending bad signals and the ground station alleged the aircraft had loose connections. The whole scheme appealed to Jones as he was a natural practical joker, and remarked that he was able to play one of the largest practical jokes with virtually any national resource that he required. The gradually increasing power conditioned the Germans such they did not realise that the system was being interfered with, but believed that it suffered several inherent defects. Eventually, as the power was increased enough, the whole ''Y-Gerät'' system started to ring with all the feedback.
The Luftwaffe, finally realising that the British had been deploying countermeasures from the very first day that the system was used operationally, completely lost faith in electronic navigation aids as the British had predicted, and did not deploy any further system against Great Britain, although by this time Hitler's attention was turning towards Eastern Europe.
See also
*
Belfast Blitz
The Belfast Blitz consisted of four German air raids on strategic targets in the city of Belfast in Northern Ireland, in April and May 1941 during World War II, causing high casualties. The first was on the night of 78 April 1941, a small attack ...
*
Chain Home
Chain Home, or CH for short, was the codename for the ring of coastal Early Warning radar stations built by the Royal Air Force (RAF) before and during the Second World War to detect and track aircraft. Initially known as RDF, and given the off ...
*
GEE, the early war RAF navigation system for night bombing
*
Kammhuber Line
The Kammhuber Line was the Allied name given to the German night air defense system established in July 1940 by Colonel Josef Kammhuber. It consisted of a series of control sectors equipped with radars and searchlights and an associated night f ...
*
List of World War II electronic warfare equipment
A ''list'' is any set of items in a row. List or lists may also refer to:
People
* List (surname)
Organizations
* List College, an undergraduate division of the Jewish Theological Seminary of America
* SC Germania List, German rugby union ...
*
Oboe
The oboe ( ) is a type of double reed woodwind instrument. Oboes are usually made of wood, but may also be made of synthetic materials, such as plastic, resin, or hybrid composites. The most common oboe plays in the treble or soprano range.
A ...
, the December 1941-launched successor to GEE for RAF night bomber raids.
Notes
Footnotes
References
*
*
*
*
* (Expanded from Episode 1 of
The Secret War (TV series)
''The Secret War'' was a seven-part television series that was produced by the BBC in conjunction with the Imperial War Museum (IWM) that documented secret technical developments during the Second World War. It first aired during 1977 and was pre ...
BBC 1977)
*
*
*
External links
Site (in German) listing locations of radio beam transmitters as well as radar early-warning stations (interesting photos and extensive list of references)
{{Use dmy dates, date=August 2019
Alexandra Palace
the Beams
Electronic countermeasures
Electronic warfare
History of telecommunications in Germany
Military history of the United Kingdom during World War II
Radio navigation
Science and technology during World War II
The Blitz
the Beams
the Beams