During the early stages of WWII, both the RAF and the German Luftwaffe were working furiously to overcome the difficulty of accurate night time navigation over blacked-out enemy territory. However, the German's stole a march on Britain by developing a novel long range radio system based on a previously shorter technique known as the Lorenz blind landing approach, which they already had in use before the war.

Most German bombers were equipped with Lorenz receivers and antennas which were used to assist in night and bad weather landings. The system operated on a radio frequency of around 30 MHz. In order to extend the range over the hundreds of miles needed to carry out accurate bombing raids a huge beam antenna with a high power transmitter was needed. The Lorenz radio receiver onboard the fighters were modified to increase their sensitivity. Developed by the Telefunken Company, the Germans gave it the codename "Knickebein".

The first Knickebein antennas were erected in Germany at Kleve, near the Dutch border and at Stollberg just South of the Danish border. But with the fall of France, beam stations were also set up much closer to Britain on the Cherbourg peninsular.

Thanks to early enigma decrypts from the code breakers at Bletchley Park, British Technical Intelligence had already received clues that a radio based navigation system was being used to guide the Luftwaffe bombing raids over central Britain. The claims of intricate German radar systems were suspected to be true but unproven until a British science advisor to MI6, Reginald Victor Jones, gathered evidence of their existence and set out to actively look for any information that might reveal the progress made by German scientists. Captured Luftwaffe aircrew and analysis of the electrical equipment found in crashed German bombers helped him to put the pieces together.

The breakthrough came when a crashed Heinkel was recovered revealing a Lorenz receiver that had been adapted with a high sensitivity add-on. Jones then convinced the High Command of the menace and special reconnaissance flights were quickly organised to hunt for beams with a Lorenz signature. One was quickly located with, not just one, but two Lorenz type beams intersecting over Derby-home of Rolls Royce Aero Engines. With the existence of the beams confirmed steps were immediately taken to find a way of neutralising them. A small team, under the direction of a young physicist, Dr Robert Cockburn, was put together in order to devise the necessary jamming equipment.

But in the meantime, the Germans were moving ahead themselves with refining their own equipment and developed a system which used 3 director beams. The added advantage of this was that the third beam acted as a semi-automated bomb release giving a signal at precisely the right moment for the aircraft to release its bombs. This meant the German's were able to carry out night time raids with devastating accuracy.

In November 1940, British radio listening stations began to pick up unusual signals from German bombers. As luck would have it, the frequencies used were within those covered by the Alexandra Palace transmitter. Engineers were bought in to reactivate the transmitter and the signal broadcast from the aircraft was picked up at AP which then re-transmitted the signals back to the beam station (on the same frequency) causing an error in the range estimations. The Alexandra Palace transmissions were sent on the bomber's receiving frequency causing the bomber to immediately re-transpond the signal back, which would be picked up by the beam station and again by the ground based receiver, resulting in a further signal being transmitted by AP and so on and so on. The result was a string of unsolicited returns to the beam station in addition to an occasional "wanted signal". This jamming system was code named "Domino" and first became active in February 1941. On the first few nights the AP transmitter was used at low power simply to confuse the Germans - who assumed that their equipment was faulty. Later, the strength of the signal was increased and it howled round like a badly set PA system - rendering the German system useless.

Then on 3rd May 1941, three German aircraft equipped with a somewhat more refined system were shot down. The transmitter units were salvaged and sent to Farnborough for analysis. The details of the beam steering system were discovered. This opened up a second jamming opportunity, as it was found that simply by transmitting a continuous modulating tone on the beam frequency, the automatic analyser on board the aircraft lost synchronisation and gave completely arbitrary steering instructions. Jammers using this technique were quickly produced and by the middle of that month the German bombers discovered that the skies over Britain had become a much more hostile place for them. A short while later, the bombing abruptly stopped. The Battle of Britain was won and Hitler turned his attention towards Russia.