There were three main German radio navigation systems. Known as X-Gerät, Knickebein and Y-Gerät, all used the same basic principle, which was first implemented for the Lorenz blind-landing system. In this system, two radio beams, next to each other but with a slight offset, were transmitted. One beam had just dots, the other just dashes. In the overlap between these two beams, the two signals combined and a steady note was formed. All the pilot had to do was fly down the overlap region, guided by the audio signal. If he was too far to one side or the other, then the signal would switch to dots or dashes, and he would know to turn back towards the centre of the beam. The Lorenz system was widely used, with the Luftwaffe, RAF and many airlines all using it.

X-Gerät was the first of the three German systems to enter use. It used six Lorenz-type beams. Three were used to mark the correct flight-path to the target. These had varying widths, and were transmitted at different frequencies. The other three intersected with these beams at three different points, and were used for accurate bombing. To use X-Gerät, an attacking aircraft would fly along the approach beams. It would encounter the first cross-beam at 50 km from the target, which served as a warning to the crew that they were approaching the target. When it crossed the second beam, 20 km from the target, the navigator started a special clock, like a stopwatch with two independent hands. The third beam was 5 km from the target. When this beam was crossed, the navigator stopped the first hand on the clock, and started the second hand moving. This rotated three times faster than the first hand. As a result, the two hands would intersect when the aircraft was over the target. When the hands intersected, the bombs were automatically dropped by an electrical system. X-Gerät was highly accurate, but it needed specialised equipment -as well as the clock and associated bomb-dropping system, it used a radio frequency that wasn't used by any other Luftwaffe radio system. Only one Luftwaffe unit, KG-100, would be equipped with it in 1940.

Knickebein was a simpler system, using two beams. One was an approach beam, the other a cross-beam. The cross-beam intersected the approach beam over the target. It used the same frequencies as the Lorenz system, so there was no need for special equipment. It was also simple enough that any Luftwaffe bomber crew could use it without additional training. However, it was also a lot less accurate than X-Gerät, as the accuracy was essentially that of the width of the cross-beam. At 180 miles from the transmitter, the width of this beam was a mile. Both Knickebein and X-Gerät were in operation when the war began.

The British began to piece together the existence of these systems from early 1940. The first clue came from the wreck of a German bomber which crashed in Scotland in October 1939. British technicians had noted that the aircraft's Lorenz receiver was unusually sensitive, but no significance was attached to this at the time. Audio recordings from bugged rooms in POW camps in late 1939 and early 1940 gave references to X-Gerät, but with little information about what it actually was. At the time, there was some speculation that it might be an airborne radar. In March 1940, a German bomber was downed. In the wreck, the crew's instructions on navigational aids were found. These included a reference to Knickebein. Later that month, more bugged conversations between POWs told the British that Knickebein was similar to X-Gerät. in May, a German airman's diary was found in a shot-down bomber, which referred to training on Knickebein. Then, on the 5th June, Bletchley Park decrypted a Luftwaffe Enigma signal that stated: "Knickebein at Kleve is confirmed at point 53° 21' N, 1°W." The coordinates corresponded to a site in Nottinghamshire, and so the decrypt prompted a search for a hidden radio beacon. When this search turned up nothing, British minds, especially that of Dr R. V. Jones, a scientist working for the Air Ministry, began to turn to radio-navigation beams. On the 14th June, this suspicion was given weight by the interrogation of another prisoner. This prisoner gave a fairly full description of Knickebein. Combined with more papers captured from downed bombers, which gave the location of two of the Knickebein transmitters, this provided the impetus for a search for the German beams.

This search was carried out by Avro Anson aircraft from the Blind Approach Development Unit. This had developed British techniques for using radio-navigation for blind landings, and so had most experience with flying Lorenz beams. The BADU pilots were accompanied by radio operators from the Y-Service, Britain's chain of radio intercept stations. While they were searching, the RAF's photo-reconnaissance units began to search for the transmitters. They couldn't reach one of the established transmitters, at Bredstadt, while sorties to the other one, at Kleve, encountered heavy cloud. They did, however, manage to find and photograph a transmitter under construction at Beaumont-Hague in northern France. On the 21st June, an Avro Anson took off from RAF Wyton. South of the town of Spalding in Lincolnshire, it located a Knickebein beam. Shortly afterwards, it found the second beam, near Beeston in Nottinghamshire. The two beams were aimed at the Rolls Royce factory in Derby, but were not located over it.

The following day, the RAF began to implement countermeasures. No. 80 Wing was set up, under the command of Wing Commander Edward Addison. Headquartered in a disused garage in Garston (near Watford), its job was to find and employ countermeasures to the German systems. Dr Robert Cockburn of the Telecommunications Research Establishment was tasked with creating tailor-made jammers for Knickebein. While these were being produced, Addison acquired a number of diathermy sets from hospitals (these used radio waves to cauterise wounds). These were modified to produce radio noise at the Knickebein frequencies, and installed in a number of police stations near likely targets. The duty constables at these stations were instructed to switch them on when instructed by 80 Wing. These were soon accompanied by modified RAF Lorenz transmitters, which, it was hoped, would bend or confuse the beams, though it soon proved that these transmitters were too weak to be effective. 80 Wing also took control over other ECM efforts (such as the use of Meacons to disrupt the German network of navigational beacons). The first specialised Knickebein jammers, nicknamed 'Aspirins', came into service in the autumn of 1940. Soon afterwards, the Germans stopped using Knickebein. The jamming was not especially effective, but it wore on the morale of German bomber crews. It showed that the British knew the beams were there, and might be concentrating night fighters and AA guns along them. Luftwaffe crews began to refuse to fly along the beams, and efforts were eventually abandoned.

As Knickebein dropped out of use, X-Gerät began to see more use. The X-Gerät signals were soon picked up by the Y Service, allowing them to pinpoint a number of the transmitters. The British also gained intelligence from analysis of bomb damage of attacked targets. Targets that were close to the approach-beam transmitter near Cherbourg were attacked with great accuracy; attacks on more distant targets were less accurate. A final, and vital source of intelligence, were Enigma decrypts. KG-100 was based at Vannes, which was not connected to the Luftwaffe's telephone network until 1941. The only way to communicate with the transmitter stations was by radio. These messages gave the British a good understanding of the mechanics and frequencies used by X-Gerät. To jam it, Cockburn modified an Army gunlaying radar to produce a jamming system codenamed 'Bromide'. These were soon being churned out, but they were flawed: they produced their Lorenz signals at 1500 Hz, as Knickebein used, rather than the 2000 Hz of X-Gerät. The filters in the X-Gerät receivers tuned out the signal. This flaw enabled KG-100 to lead the devastating attack on Coventry on 14th November 1940 despite the presence of a number of Bromide jammers. The British were informed of the flaw when they examined the wreck of a bomber which had been led astray by one of the Meacons and crashed off the Somerset coast on the 6th November - examination of the wreck was delayed slightly by inter-service rivalry between the RN, RAF and Army. With the frequency corrected, and more jammers entering service, X-Gerät began to lose its effectiveness. Its effectiveness had also been limited by the flaws in the Luftwaffe's pathfinding doctrine, which made it difficult to tell the difference between fires started by the pathfinders and those started by bombers dropping in the wrong place.