[7.0] The Battle Of The Beams

v2.0.5 / chapter 7 of 12 / 01 feb 13 / greg goebel / public domain

* The increased use of electronics in warfare led to a wide range of consequences. One was the need to determine what electronics systems the enemy was using, and to develop countermeasures against them. The British were pioneers in this aspect of electronic warfare, unraveling the secrets of German radio navigation systems and then jamming them during the Blitz.

Unknown to the British, the Germans had also developed radar equipment, some of it better than its Allied contemporaries. The British would become aware of German radar and go to great lengths to learn more about it, including carrying off a daring commando raid.

While the Allies and the Germans were developing radar systems, the Japanese were working on their own types of radars, as well as putting captured equipment into production. The Japanese badly lagged Allied radar technology, though for the moment the Allies had no idea that Japan had any radars at all.

Seetakt coastal radar



* In November 1939, a civilian technical expert in the employ of the British Air Ministry named Reginald Victor Jones was given a package. Dr. R.V. Jones was another of the significant players in the Wizard War. He was a tall, athletic Scotsman with a physics doctorate from Balliol College at Oxford, where he had been a protege of Professor Lindemann. Jones had a sharp sense of humor, and the deductive ability of a technical Sherlock Holmes. He had turned down a job offer at Mount Wilson Observatory in California to sign on with the Air Ministry's "Scientific Information Branch (SIB)". When offered the SIB job, he replied: "A man in that position could lose the war. I'll take it."

At the time, he essentially was the SIB, since he was the only RAF official working on technical intelligence, and indeed some claim he all but invented the field. In time, he would become "Assistant Director of Intelligence (Science)", making him the highest ranking civilian on the Air Staff.

His first major assignment was to inspect a set of papers on German technology. The package of papers included seven pages of text in German, along with English translation. They had been passed on from the British embassy in Oslo, Norway, which had been given them anonymously. If taken at face value, the papers seemed to be a treasure chest of information on secret German weapons development efforts. The "Oslo Report" talked about many things, including guided bombs, rocket-propelled aircraft, and particularly radio navigation schemes. The papers had been provided by an anti-Nazi German researcher named Hans Ferdinand Mayer, but his identity did not become known until well after the war, and even then his identity was kept quiet to prevent him from being harassed as a traitor by other Germans. Mayer was imprisoned for a time during the war for speaking his mind too freely. Clearly nobody really suspected he had been giving away secrets as well, since he would have been executed, probably after the Gestapo got bored of torturing him.

Many British officials thought the Oslo Report was a ruse, as it contained implausible statements, such as claiming that 5,000 Junkers Ju-88 bombers were being produced a month. R.V. Jones thought it was for real, since it gave up too much verifiable and valuable technical information. He judged the implausible statements to be merely errors. The Oslo Report mentioned in a vague way what seemed to be German radar and a radio navigation system. The war was quiet at the time, and nothing more came of the leads for the moment. Jones didn't forget about it, however.

* In March 1940, Jones received information obtained from German prisoners and a scrap of paper found in a downed German bomber that hinted at the existence of two German radio-navigation systems. Oddly, from what Jones could make of these two systems, they didn't match anything in the Oslo Report. Some of the German prisoners had mentioned an electronic system named "X-Geraet (X-Device)", but gave no details.

On 5 June 1940, the evacuation of British troops from Dunkirk in France was completed. On that same day, an RAF signals intercept station picked up a coded German radio transmission. The message was passed to the British cipher-breaking establishment at Bletchley Park in the English Midlands. The Germans had developed a machine called "Enigma" to encipher their messages. The Germans believed Enigma messages were absolutely secure, but the British codebreakers had cracked the cipher. The Enigma-encrypted message of 5 June was from Luftwaffe headquarters. The message was passed on to Jones and mentioned three things:

This was the first significant clue on the mystery of the German radio navigation systems. Jones felt increasingly certain that the Germans did in fact have one or more radio navigation systems that could be used for night or foul-weather bombing.

* Jones focused on the possibility of a radio navigation system that involved narrow radio beams sent out from two widely separated locations. The two beams would intersect over a target city, marking it for bombing. Jones further concluded that Knickebein was a receiver installed in a bomber that allowed the aircraft to use such a radio navigation system.

He then performed a careful inspection of a Luftwaffe Heinkel He-111 bomber that had been forced down in Scotland in October 1939. The He-111 was fitted with a "Lorenz" blind-landing set, an electronic landing aid to help bring the aircraft back to ground safely at night or in bad weather.

Lorenz, named for its manufacturer, the Lorenz company, had been initially put into service for Lufthansa in 1934 and was adopted in many other countries. It was an elegantly simple scheme. It sent out a directional signal with an audio tone on a carrier in a range of wavelengths near 10 meters (30 MHz), using an antenna that switched between two transmission lobes, skewed on alternating sides of the antenna's centerline. The switching was performed by a mechanically driven cam that ensured that the signal was activated for short time in one lobe and for a long time in the second.

The signal from the first lobe would be received as a series of Morse code "dots", while the signal from the second lobe would be received as a series of "dashes". If an aircraft was on the centerline between the two lobes, the receiver would effectively get a continuous tone, with the dots filling in the dashes. If the aircraft drifted off the centerline in the direction of the first lobe, dots would gradually emerge from the continuous tone, and if it drifted off in the other direction, dashes would emerge.

Lorenz had been in common use since the mid-1930s and nobody thought it anything out of the ordinary. Having been designed as an airport approach aid, it wasn't useful for long-range air navigation, with an error of about 8 kilometers at a distance of 100 kilometers. On reexamination, the Lorenz set on the He-111 proved to be unusually sensitive, and it appeared that it was being used as a long-range radio navigation device. Armed with this clue, British interrogators managed to pry information from a captured Luftwaffe airman that confirmed that suspicion.

Knickebein did use two transmitters, both essentially refined versions of Lorenz with much greater accuracy, a few hundred meters at the maximum range of the system, which was limited by the line of sight. Like Lorenz, Knickebein operated around 10 meters (30 MHz), which allowed enhanced Lorenz receivers as discovered by the British to track the beams.

The two transmitters were set up at separate locations, with both focused on the target. A bomber would fly up one beam staying on track by listening for dots or dashes emerging from the continuous tone, and drop bombs when the second beam was detected, which was apparently transmitted on a different frequency within the operating band. The system, which had been initially demonstrated in 1937, was actually known to the Germans officially as "X-Leitstrahlbake (Direction Beacon)", and had been given the nickname "Knickebein" due to the bent appearance of the primary transmitting antenna.

* On 21 June, much to his surprise, Jones was called to a meeting of Churchill's cabinet at 10 Downing Street. The invitation was at the suggestion of Lord Cherwell, Jones' mentor at Balliol College. The meeting concerned the possibility that the Luftwaffe did in fact have radio navigation systems. Churchill was extremely worried that such systems would allow the Germans to perform accurate attacks at night, overstraining Britain's air defenses.

Not everyone at the meeting believed that such radio navigation systems were possible, and the group had been arguing the matter before Jones arrived. When Churchill asked Jones a question, Jones tactfully offered to outline what he knew about German radio navigation systems. Churchill agreed, and Jones spent twenty minutes describing the intelligence he had received, and his deductions. Jones told the group that he did believe that the Luftwaffe had radio navigation systems, and suggested that they could be disrupted. Churchill was impressed by Jones, always liked the idea of fighting back, and gave him the authority to investigate further.

* First, Jones needed to obtain solid proof of his suspicions. Three Avro Anson utility aircraft were fitted with American Halicrafters S-27 wideband radio receivers, used by radio amateurs, with operators tuning the receivers to possible Knickebein transmission frequencies. Although the receivers found nothing of interest at first, greatly worrying Jones, one of the Ansons finally picked up a Knickebein transmission, and the flight crew flew down the beam of the signal until they received the second signal at the intersection point of the two beams.

With this proof in hand, Jones went to the TRE to devise countermeasures, working with the TRE's Robert Cockburn, a former master of a municipal college. Electrodiathermy sets, used in hospitals to electrically cauterize wounds were pressed into service as "broadband jammers", throwing out radio noise over a wide range of frequencies to disrupt Knickebein transmissions. RAF Lorenz transmitters were also modified to produce false Knickebein signals in hopes of confusing Luftwaffe bombers.

By September 1940, when the Luftwaffe turned to night raids, countermeasures against Knickebein had been refined. The British were operating more powerful anti-Knickebein transmitters that degraded Knickebein signals by injecting them with Morse code patterns. Since the beams were codenamed "Headaches", the transmitters were named "Aspirins".

Knickebein had been neutralized. Without direction, German bombers sometimes got lost in the dark, and at least one crashed because the pilot became completely disoriented, losing control of his aircraft and causing his crew to bail out before the bomber slammed into the ground. Cockburn and his team at the TRE had achieved their success in the jamming business, and would continue successfully in the trade for the rest of the war.



* Jones knew from his intelligence that Knickebein wasn't the only German air navigation system. In mid-August, an RAF signals intercept station picked up a Luftwaffe transmission outside the normal range of Luftwaffe radio traffic frequencies. The signal resembled that used by Knickebein, and Jones suspected it was for X-Geraet, the second radio navigation system German prisoners had mentioned.

Radio direction finders located transmitting stations at Cherbourg and the Pas des Calais in France, and within a few weeks British intelligence had linked the signals to a single Luftwaffe bomber unit, Kampfgruppe 100 (KG-100). KG-100 appeared to be operating independently of other bomber units, and their attacks also appeared to be unusually accurate. British army radar transmitters were quickly modified to jam the "X-beams", as they were known. Following the earlier designation of "Aspirins", the new jammers were called "Bromides".

In October, KG-100 began to drop incendiary bombs. Lord Cherwell and Jones concluded the unit was being used for "pathfinding", marking targets for attacks by other Luftwaffe units. More information was obtained from a KG-100 He-111 that had splashed down in the shallows off the coast of southwest England. Two damp X-beam receivers were recovered from the wreck.

On the night of 14 November 1940, the Luftwaffe launched a massive attack on the city of Coventry, a center of weapons production in the English midlands. KG-100 was to act as pathfinder, using X-Geraet for navigation. KG-100 bombers took off from their base at Vannes in France, and flew over the transmitter at Cherbourg, which was codenamed WESER and was pointed at Coventry. A bomber would then ride the WESER beam, using a needle indicator to detect deviations from course. As a bomber approached the target, it intercepted a beam from a transmitter in the Pas de Calais, codenamed RHEIN. 30 kilometers (18.6 miles) short of the target, the bomber intercepted a second beam from the same transmitter, codenamed ODIN. The bombardier set a timer. 15 kilometers (9.3 miles) in front of the target, the bomber intersected a third beam named ELBE. The bombardier hit the timer again, calibrating it so that it would automatically release the bombs when it counted down to zero.

Using X-Geraet, KG-100 pathfinders successfully marked Coventry as a target with their incendiaries. British X-Geraet jammer stations were slightly off frequency and failed to confuse the pathfinders. Three main Luftwaffe bomber streams KG-100 followed, and dumped their bombloads on the city. Damage to Coventry was widespread, with many civilians killed or injured.

On 19 November, the Luftwaffe attacked Birmingham. The British jammers were on frequency and German bombing accuracy was poor. The Luftwaffe enjoyed some success in December against British cities not protected by jammers, but by January 1941, the British had plugged all the holes. X-Geraet had been defeated. Unfortunately, London continued to suffer, since it was much too big and easy a target.

X-Geraet was actually just a straightforward derivative of Knickebein. The Knickebein antenna was big, clumsy, hard to move around and site, so the Germans had developed a modified system with a smaller, much more convenient antenna. However, although the smaller antenna did give a nice tight beam, it actually generated 14 individual beams of equal strength, which was why a bomber had to pass through multiple "checkpoints" before dropping its bombs. X-Geraet operated around 5 meters (60 MHz), not 10 meters (30 MHz) like Knickebein, and as mentioned the receiver converted the signal deviations into a needle movement.



* Jones had believed since the beginning of the countermeasures effort that the Luftwaffe had a third radio navigation system, since the sketchy details of the system described in the Oslo Report didn't seem to match either Knickebein or X-Geraet. Jones had received reports that the Germans were setting up new transmitting antennas of some sort near Cherbourg and Brest. They were codenamed "Wotan" by the Germans, and Jones felt the name was a clue: in Nordic mythology, Wotan had only one eye.

That sounded more like the system described in the Oslo Report. In November 1940, the British intercepted an Enigma-encrypted message to a known beam transmitting station that gave a single set of coordinates for a target, which matched those of a British Army training center in Dorset. This established that the Germans had a navigation system that only needed one beam. RAF electronic intelligence centers located a suspicious transmission between 7.14 and 6.25 meters (42 and 48 MHz). Examination of the signals on an oscilloscope finally showed what the Germans were doing.

The German navigation system provided a complicated signal that, like X-Geraet, a Luftwaffe bomber with the proper equipment could use to stay on path to the target. However, the navigation system also transmitted a second signal, which the bomber's equipment reradiated on a slightly different frequency. The phase difference between the original and reradiated signal increased as the bomber flew away from the transmitter, giving an indication of range. When the bomber was over the target, the flightcrew were told by radio to drop their bombs. The Germans called the system "Y-Geraet (Y-Device)", or "Wotan 2". "Wotan 1" had actually been X-Geraet, which meant that Jones had come to the right conclusion for the wrong reasons. Y-Geraet had been developed from X-Geraet to eliminate the clumsy requirement for a second transmitter and get rid of the complications imposed by the multiple signal lobes of the earlier system.

National television broadcasting had begun in Britain just before the war, and the BBC had a large TV transmitting station in London. This transmitting station was used to pick up the Y-Geraet transmissions and, in conjunction with supporting ground stations, shoot them back on the same frequency at high power. This jamming system was in place by the end of February 1941 and confused the Luftwaffe considerably. Y-Geraet was jammed the very first time it was used in combat, and British listening stations overheard angry remarks from Luftwaffe crews back to their ground controllers. More sophisticated jammers would be developed in a few months.

By May, with the withdrawal of the Luftwaffe for the attack on the Soviet Union, the Blitz and the "Battle of the Beams", as it would be called, were over. Although the British were spared bombing raids for the moment, their electronic wizards were not idle. The Germans had set up air navigation transmitters beacons in France, Germany, and Norway. The British set up fake beacons, or "me-cons", to confuse German aviators, with considerable success. They managed to con one Ju-88 and one Do-217 bomber to land on RAF airbases in England by mistake.



* By this time, the British were becoming aware of German radar technology as well. Early in the war, the British high command had believed the Germans knew little or nothing about radar, but at the outbreak of the conflict the Germans had a set of effective longwave radars, and in fact some of their gear was the best in its class at the time. Like the Americans, the Germans started out focusing on short wavelengths, but were forced by realities to move to longer wavelengths.

One of the most prominent figure in German radar development was Dr. Rudolf Kuenhold. In the early 1930s, Kuenhold had worked for the German Navy's Signals Research Division. He had helped develop German sonar, and felt the same principles could be used with radio beams. Kuenhold and an assistant developed this idea in collaboration with a firm named "Gesselschaft fuer Elektroakustiche und Mechanische Apparte (GEMA)".

The German researchers put together a continuous wave radar system, and in March 1934 they used it to detect a battleship in Kiel harbor. By May 1935, they were working with pulsed radar, a few months behind the Americans and the British, and obtained funding from the Kriegsmarine, the German Navy. The Germans called the technology "FunkMessGeraet (Radio Measuring Device)", a name as bland and misleading as the British term "RDF".

German progress on radar actually outpaced that of the British, at least at first. Kuenhold focused on short wavelengths while other German researchers felt, correctly, that longer wavelengths would be easier to deal with and more effective, at least for the time being. The result was two lines of development, one focused on short wavelengths for naval use, and the other focused on long wavelengths for early warning.

* The short wavelength naval radar became the "Seetakt" series. Prototype models operated around 50 cm (600 MHz), but this proved troublesome. The first fully operational model, installed on the pocket battleship GRAF SPEE in January 1938, operated around 60 cm (500 MHz), but later production operated over the range of 82 to 77 centimeters (368 to 390 MHz). Pulse width was 3 microseconds, peak power was 8 kW, and the PRF was 500 Hz. Maximum range against a ship-sized target at sea was up to 220 kilometers (100 miles) on a good day, though more typically about half that.

About 200 Seetakts were built. They were installed on warships and also used, in fact in greater numbers, for coastal defense. There was an attempt to fit Seetakt to U-boats, but it didn't prove practical. The Kriegsmarine had Seetakt in operation on their surface vessels months before the British or the Americans had an operational radar on any of their warships. However, this progressiveness was only due to the initiative of a few officers who didn't make policy, and otherwise the Kriegsmarine's radar effort suffered from the same problem that would afflict Germany's technical efforts all through World War II: little or scatterbrained direction from the top.

The Kriegsmarine regarded radar as a low priority and were conservative in their specifications, insisting on reliability and simplicity at the expense of capability. They wanted Seetakt to be used primarily for ranging, with detection of vessels and obstacles in night and foul weather as a secondary objective. Precision fire-control was not an objective, at least initially.

There were related problems at the bottom. GEMA didn't have experience at building electronic systems for the harsh shipboard environment and had to suffer through a painful learning curve. The low priority of their work also meant that they had to deal with poorly trained crewmen, a problem compounded by the fact that demands for secrecy kept detailed documentation, such as circuit diagrams, out of the hands of users for some time. The effort was generally left to fumble on its own.

* One of the other aspects of this indifferent attitude was that the Kriegsmarine hadn't wanted to use the long wavelength early warning radar on board ships, believing for some reason that it should be reserved for land use. First tests of what would become GEMA's "Freya" early warning radar were conducted in early 1937, with initial delivery of an operational radar to the Kriegsmarine in 1938.

Freya operated in the band from 2.5 to 2.3 meters (120 to 130 MHz), with a pulse width of 3 microseconds, a peak power output of 15 to 20 kW, and a PRF of 500 Hz. It had a maximum range of only 160 kilometers (100 miles) and could not accurately determine altitude, making it inferior to Chain Home in those respects, but it was a fully steerable and mobile system. Over a thousand would be built in all during the war.

Freya radar

Another element that hobbled German military technology development was interservice rivalry. This existed -- always has and always will -- in the military services of other nations, but the Kriegsmarine kept their work a complete secret from the rival service branches. Hermann Goering didn't find out about the Kriegsmarine's work until July 1938, and he was outraged that he hadn't been informed of it. He was more or less told that what the Kriegsmarine did was none of the Luftwaffe's concern, and that if the Luftwaffe wanted radars they could get them themselves. As it turned out, Wolfgang Martini quickly got in touch with GEMA to obtain Freyas for the Luftwaffe, though the Kriegsmarine did everything they could to interfere and would continue to try to block Luftwaffe access to GEMA through most of the rest of the war.

* While Kuenhold and his colleagues at GEMA were working on what would become Seetakt and Freya, an independent radar effort was underway at the German electronics giant Telefunken, under the direction of Dr. Wilhelm Runge, the company's lab director. Kuenhold had actually discussed radar technology with Runge late in 1933, but Runge regarded the whole idea as science fiction, and was rude about it to Kuenhold. Kuenhold didn't forget the snub, ensuring that the two radar development groups had little or no contact with each other in the future.

Runge performed some simple experiments with continuous-wave radar in 1935 and determined that the concept wasn't as much science fiction as he had thought. By 1936, he was demonstrating a pulsed radar with a single, duplexed antenna. Improvements in transmitter power led to the demonstration of a practical gun-laying radar to the German Army in July 1939.

The Telefunken radar operated in the range of 54 to 53 cm (553 to 566 MHz), an extremely short wavelength for the time, with a pulse length of 2 microseconds, a peak power of 7 to 11 kW, and a PRF of 3,750 Hz. Range was about 29 kilometers (18 miles). Runge liked to give his projects geographical names, and the radar was given the name "Wuerzburg" by the simple measure of sticking a pin into a map haphazardly and hitting the city of that name.

The initial "Wuerzburg A" model used a steerable paraboloid dish antenna to focus on targets. The next production model, the "Wuerzburg C", added lobe switching for greater accuracy, and the definitive "Wuerzburg D", introduced in 1941, featured conical scanning, using a offset receiver feed that spun at 25 Hz, called a "Quirl". Even the Wuerzburg A was very accurate, and the Army was highly impressed. While the Lorenz company had also been working on a gun-laying radar, the military chose the Telefunken design and had it put in production. The Wuerzburg went into service in 1940 and over 3,000 of all variants were built.

* By the end of 1939, GEMA had produced only four Seetakt and eight Freya sets. The poor reliability of the Kriegsmarine's Seetakts had limited their usefulness, though the ADMIRAL GRAF SPEE had made good use of the radar during its cruise around the Atlantic.

The GRAF SPEE got into a fight with three British cruisers on 13 December 1939, and though the British were badly mauled, the German raider had to seek shelter in the harbor of Montevideo, Uruguay. The raider's captain was misled by a British radio signals deception effort into thinking that a powerful Royal Navy force was waiting for him. Since the ship would be interned if it remained in harbor much longer, he took the vessel out to sea the next day, scuttled her, returned to his hotel room in Montevideo, and put a bullet in his head. The British inspected the wreck and wrote up a report about Seetakt. Nobody seems to have paid it much mind, except for R.V. Jones, who found it extremely interesting.

The Freyas back in Germany were operating independently and on a more or less experimental basis, complementing the existing network of ground observers. The ground observer network was Germany's answer to the British ROC and featured groups of observation posts reporting to district command posts. Even the modest integration of the radars into this network paid off handsomely. On 18 December 1939, two Freyas picked up a formation of 18 RAF Wellington bombers on a daylight raid, and helped direct fighter defenses to the intruders via radio. Only half the bombers returned to Britain. The bomber might always get through -- but getting back home again in one piece was another question.

German radars had become arguably the most sophisticated of their generation, with the Freya much more the shape of things to come than the British Chain Home, and the Wuerzburg clearly superior to any other gun-laying radar before the SCR-584. However, characteristically, while the Germans had been technically clever, they were slow to match the insight of the British in setting up the well-organized filter room system.

Radar had so far been not much more than a toy to most of the German brass, but the 18 December incident made a strong impression on the Luftwaffe, and by the beginning of spring 1940, they had set up a chain of 11 Freyas to protect Germany's western frontier. They still were being used as part of the ground observer network, which featured nothing as well thought-out as the British filter room scheme, but ideas were floating around for improvements.

After Hitler's conquest of Western Europe in the spring of 1940, Freya stations popped up along the Atlantic coast. As British night raids began to ramp up, Goering decided to improve the defensive system. Colonel Josef Kammhuber was assigned to the task, and began to assemble a more effective air defense network, described in detail later.



* Although British military brass was slow to become aware of German radar, R.V. Jones had not been so complacent. The Oslo Report had mentioned radar, and in July 1940 Jones was given a cryptic scrap of intelligence that mentioned a "Freya" warning system for air defense.

Jones knew Freya was a Norse goddess, and looked her up in a book on mythology. Freya was a fertility goddess, something like a Nordic Venus, which helped Jones not at all, but then he found that she had a necklace that was guarded by the watchman Heimdall, who could see to the horizon in day or night. That hinted at radar to Jones. By the way, this illustrates why modern secret military projects are assigned names chosen at random as a standard practice.

Jones even received intelligence on the possible location of Freya stations, but air reconnaissance of the sites through the summer and early fall of 1940 turned up nothing. British signals intelligence had in fact picked up Freya emissions, but they were confused with emissions from British gear and disregarded.

The Oslo Report had also mentioned a second radar that operated at 50 cm (600 MHz). While Jones was closing in on Freya, he received an Enigma decrypt that stated an otherwise undescribed "Wuerzburg" was being sent to Rumania, a German ally. Jones suspected that Wuerzburg was the 50 cm (600 MHz) radar, but for the moment the German radars remained hidden in shadows.

* In the meantime, one of Jones' people, Derek Garrard, did some detective work of his own. The Straits of Dover were a chokepoint where any shipping traffic passing through would find it very difficult to avoid being detected by radar, even if they hugged their respective "friendly" shores. The British had CHL stations at Dover to spot German shipping, and so if the Germans had radars they likely had set them up on the opposite shore, at Calais, to spot British shipping. Garrard took a set of Halicrafters S-27 radio receivers, put them in his car, drove to Dover with a tech crew, and set them up. The receivers quickly picked up Seetakt emissions.

Either because of security barriers or simple fumbling, the Royal Navy wasn't informed of the German radars at Calais. In November, some weeks after Garrard's discovery, the Royal Navy began to suspect the Germans had radar in the area after German shore batteries in the Calais area had directed accurate fire on a British convoy at night.

His Majesty's Signal School got a call asking them to investigate, and a Marconi radio engineer named N.E. Davis quickly arrived at Dover with a wideband radio receiver. Davis also found the Seetakt emissions, but went further and wired up jammers to blind the Seetakts. By February 1941, there were six improvised jammers set up in the Dover area. They would be quickly replaced by production jammer sets, with the designation "Navy Type 91". When Wuerzburgs were detected in the Calais area, the frequency range of the Type 91s was extended to deal with them as well.

That kicked off the radar countermeasures war. To avoid further embarrassing duplications of effort, the British formed an interservice organization to coordinate signals intelligence efforts. The group was given the bland name of "Noise Investigation Bureau" to conceal its purpose, with the name reflecting a bit of dry British humor as well.

* By this time, R.V. Jones was closing in on Freya. The RAF's "Photographic Reconnaissance Unit (PRU)" was operating camera-equipped Supermarine Spitfire fighters, stripped of armament to reduce weight and increase speed, on fast dashes over occupied Europe to keep an eye on German activities.

In January 1941, a PRU Spitfire took pictures of some type of installation with two squarish objects that could be antennas, each about six meters (20 feet) wide. The aircraft had taken several pictures of the objects on its camera pass, and consecutive pictures seemed to show one of them was rotating. Ground-based signals collection had detected what Jones believed to be a Freya in the area, and he requested additional reconnaissance overflights of the target. Due to the complications of war he was not able to get new pictures of the site until 23 February. Fortunately, the new images were very clear. Jones was certain he was looking at radar system, and the brass found his evidence convincing as well.

The RAF then fitted a flight of Vickers Wellington bombers in Number 109 Squadron with wideband receivers to perform signals intelligence over Europe. The aircraft were called "ferrets", which has since become the general name for a signals intelligence platform. They picked up more of the 2.4 meter (125 MHz) Freya emissions, and in May 1941 found the 50 cm (600 MHz) signals from Wuerzburg.

By the fall, the ferrets had located 27 Freyas and 9 Wuerzburgs, though the exact location of the Wuerzburgs and their appearance remained unknown. It did seem to be a very capable set, with a narrow beam and high accuracy, and in fact, as mentioned, at the time it was the best radar in its class anywhere. R.V. Jones was determined to learn more.

* While the British were trying to come to grips with German radars, the Germans were trying to come to grips with theirs. In early 1942, the Germans set up jammers on Sicily to blind the radars used for the defense of the island of Malta, but R.V. Jones outsmarted them. He told the operators on Malta to go on using the radars as if they were perfectly effective, and local expertise managed to come up with some ways of "looking through" the jamming. The Germans decided the jamming didn't work at all and gave up on it.

The Germans won a few as well. In early 1942, Hitler summarily ordered the Kriegsmarine to move the battlecruisers SCHARNHORST and GNEISENAU and the cruiser PRINZ EUGEN, from their port at Brest, France, on the Bay of Biscay, to ports where they could protect Norway from a possible Allied invasion. The admirals thought the Royal Navy would certainly send all three vessels to the bottom, but naval planning staffs managed to come up with a detailed plan that gave the warships a very good chance of survival as they dashed north through the English Channel.

Since the vessels could be detected by British CHL radars as they passed through the Dover Straits, one of the items in the plan was to jam the radars. Wolfgang Martini, now in overall command of the German signals establishment, set up 1.5 meter (200 MHz) jammers on the other side of the straits and had the operators turn up the power slowly, day by day, until their output power was adequate to hide the ships. A British Army officer in the area realized the Germans were up to something and told his superiors. They ignored him, and he went to R.V. Jones, who promptly sent TRE engineers down to Dover to figure out what was going on.

They were too late. The German operation began after dark on the evening of 11 February 1942. The warships maintained complete radio silence, not even using their Seetakt radar sets, with navigation fixes to be provided in principle by shore stations. The next day the TRE staffers could do nothing but watch the German warships move up the channel. The warships were heavily protected by a screen of escort vessels and fighter cover, and the British attacks were uncoordinated, ineffective, and in some cases suicidal. One flight of Fairey Swordfish biplane torpedo-bombers was completely wiped out.

Although the SCHARNHORST and the GNEISENAU both hit mines, they made it to port. Churchill was enraged at the escape of the two warships under the nose of the powerful Royal Navy, and there was a public outcry. In reality, the three warships had removed themselves to the edges of the game board, reducing the Royal Navy's worries in home waters, but the failure to sink the German vessels was still a humiliation.



* In the months leading up to the Channel Dash, R.V. Jones had been ramping up his hunt for Wuerzburg. Jones requested intensive aerial reconnaissance of known Freya sites in hopes they would turn up a Wuerzburg as well. On 22 November 1941, a PRU Spitfire had taken a picture of a radar site at Bruneval, a village on the French coast near Le Havre, that revealed a suspicious, indistinct object sited at the end of a path leading from the station.

Word of the mysterious object reached a daring RAF reconnaissance pilot, Flight Lieutenant Tony Hill, who decided to investigate personally. He overflew the site in his Spitfire on 5 December. The pictures revealed a neat radar dish about 3 meters (10 feet) in diameter. Jones decided it had to be Wuerzburg. Further reconnaissance missions over other locations revealed more Wuerzburgs, plus a new radar that other intelligence tagged as "Wuerzburg-Riese (Giant Wuerzburg)", of which more is said later.

* Jones suspected that Wuerzburg was critical to German air defenses and that the British needed to learn about it in detail. The German radar site at Bruneval was near the sea and had a convenient beach, raising the possibility that it could be seized in a raid. Jones hesitated to recommend such a risky plan but became convinced that it was justified. Churchill was enthusiastic about raids, both to bolster British morale and to keep the Germans off-balance, so a request went upstairs to Lord Louis Mountbatten, Chief of Combined Operations.

Mountbatten like the idea very much, and so a plan was devised to send in a team of paratroopers to photograph the radar in detail and carry off whatever components they could. A technical specialist was trained to make the jump with them and inspect the radar. The group would be picked up off the beach by a small naval task force. The operation was codenamed BITING.

On 27 February 1942, the raiding party -- consisting of 120 Scotsmen under Major John Frost and an RAF technician, Flight Sergeant Charles Cox -- was dropped on Bruneval from twelve Armstrong-Whitworth Whitley bombers. Nothing went very much according to plan, but the raiders improvised competently and the raid was a success, with the paratroopers returning with vital Wuerzburg components, and a technician as a prisoner. Two British were killed and four taken prisoner, all four of the prisoners surviving the war. Five Germans were killed and two taken prisoner, including the technician.

British examination of the Wuerzburg components showed that it operated over a very narrow band, and had no provisions for dealing with countermeasures. It was much better built than British radars, with a modular design that made hunting down faults relatively simple. On the other hand, the German technician proved to be much more poorly trained than his British counterparts.

BITING was the first operation of the newly-minted British paratrooper force, and a significant boost to British public morale at a time when the war was not going well for the Allies. It did much to make up for the failure to stop the Channel Dash two weeks earlier. Even the Germans, who generally had a low opinion of British troops, were impressed with the skill and dash of the raiders, and it remains the stuff of action movies.

Ironically, the success of BITING made the brass worry that the Germans might pull the same stunt on the TRE at Swanage, and so intelligence about German paratroops across the Channel quickly forced the mad relocation of the TRE to Malvern. The Germans, who were notoriously hard to trick the same way twice, also promptly fortified their radar stations. A raid to seize Freya components on 17 August 1942, during the hideously botched "practice invasion" on the French port of Dieppe, ran into stiff German defenses and went home empty-handed. In compensation, the fortified radar stations were easy to spot and, if necessary, target.



* While the British were coming to grips with German radar, the Japanese were developing their own radar systems completely out of sight of Allied intelligence.

The main reason the Japanese effort remained unknown was because it lagged so far behind Allied and German efforts. Ironically, the Japanese had good technical minds, and had even developed an effective cavity magnetron in 1939, well before the British. However, the country's militaristic leadership was focused on "bushido", the "warrior ethic", and did not give technical development high priority, tending to think that discipline, aggressiveness, and suicidal courage would always carry the day -- with the end result that sometimes the role of sensibility and cleverness in the mix was under-appreciated. Limited resources also played a role.

Substantially compounding such problems was the interservice rivalry between the Imperial Japanese Army (IJA) and Imperial Japanese Navy (IJN), which was even worse than German interservice rivalries, approaching a lunatic comedy at times, squabbling like "dogs and monkeys" as the Japanese saying has it. The IJA was modeled on the Kaiser's army, while the IJN was modeled on the British Royal Navy, and to an extent both organizations retained the mindsets of their "parents". The fact that the military dominated the civilian government, instead of the other way around, left no higher power to straighten out the feud, or to create any higher-level research organization like the US OSRD.

The Japanese had tinkered with aircraft interference detection schemes in the late 1930s, developing a system that detected aircraft flying through a beam sent from a transmitter and receiver separated by up to hundreds of kilometers, operating at 7.5 to 3.75 meters (40 to 80 MHz). This system could only detect that an aircraft was flying through the beam somewhere, providing little or no other information, but was actually deployed beginning in the 1940:1941 timeframe as the "IJA Type A". About a hundred stations were set up, apparently mostly in China.

The Japanese were slow to get started on pulsed radar. In early 1941, Japanese technical experts paid a visit to Germany to trade information with their Axis ally. Characteristically, the IJA and IJN each sent their own team, with no real coordination of their travel plans or their meetings with their hosts. When they got to Germany, it didn't turn out to be another Tizard mission. The Germans and Japanese were careful about what they told each other. The Japanese were allowed to inspect a Wuerzburg for a short time, but although they saw a Freya, the Germans wouldn't talk to them about it. On their own part, the Japanese didn't mention their cavity magnetron. It appears the Germans thought the Japanese had little to teach them, and the Japanese might have believed the same thing themselves, since the Germans seemed so obviously far ahead of them. There was no point in bargaining over the cavity magnetron if it was almost certainly nothing new to the Germans. Whatever the case, the failure to communicate was a benefit to the Allied cause.

* The Japanese returned home that summer. In the meantime, the IJN had become alarmed over evidence of Allied naval radars, and when the experts returned the Navy began an effort to develop radars of their own. The experts quickly threw together a pulse-radar prototype, operating at 4.2 meters (71.4 MHz), and had a 3 meter (100 MHz) fixed-site warning radar set designated "IJN Mark I Model 1" in production in the fall of 1941. Pulse width was long, from 10 to 30 microseconds, peak power was 5 kW, and maximum range was about 145 kilometers (90 miles). PRF was apparently variable, in the range of 530 to 1,250 Hz. About 80 were built.

Incidentally, the designation scheme is a bit confusing, and an interesting minor example of the way that Easterners and Westerners tend to think sideways relative to each other. The mark number actually specified the class of radar, with a "Mark I" being a land-based set, "Mark II" a shipboard set, "Mark IV" being a fire-control radar, and "Mark VI" being an airborne radar. The model number actually specified the type sequence of a radar within its class.

The IJN Mark I Model 1 was a crude set, but the speed with which it was developed was impressive, another demonstration that if the Japanese were slow in radars it wasn't for lack of talent. They went from this set to a shipboard air and surface search set, the "IJN Mark II Model 1". Like the IJN Mark I Model 1, the pulse width was from 10 to 30 microseconds, peak power was 5 kW, and the PRF was similar, 500 to 1,100 Hz. The major difference was that the Mark II Model 1 operated around 1.5 meters (200 MHz). Maximum range for an aerial target was about 145 kilometers (90 miles), and roughly a fifth of that for a large naval target.

About 80 IJN Mark II Model 1s were built. Unfortunately, as was often the case with early shipboard sets built by other combatants, the Mark II Model 1 wasn't reliable enough to put up with harsh sea conditions, and feedback from Imperial Navy crews was very negative.

* The IJA was pursuing its own, of course almost completely independent, radar development effort in parallel. They had limited success, building a few preliminary types that proved totally unsuitable for field use, but then coming up with a 4 meter (71.4 MHz) warning-radar set designated the "IJA Tachi 6". It was a floodlight system, comparable to Chain Home in many ways, featuring an omnidirectional or wide angle transmitter with three or four moveable, steerable receiver antennas. The Tachi 6 had a pulse width of 25 to 35 microseconds, a peak power of 10 to 50 kW, a PRF that could be switched from 500 to 1,000 Hz, and a maximum range of 300 kilometers (185 miles). About 350 were built, first going into operational service in 1942.

The IJA radar designation scheme is also a bit confusing. "Tachi" is a hybrid word, with the "Ta" standing for the "Tama Institute", the IJA organization that did the technical work, and "chi" derived from the Japanese word for "Earth", and so the word means "Tama Institute ground-based radar".

Similarly, "Tase" meant a shipboard radar and "Taki" meant an aircraft-based radar, though the IJA would never actually field a Tase radar. That might seem logical, since a shipboard radar was clearly the province of the IJN, but it is interesting to note that the IJA actually built their own submarines during the war as supply vessels for isolated island outposts, a particularly vivid example of the way the two services worked at cross purposes.