Night Level-Bombing Navigation Tactics
Knickebein (crooked leg)
The Knickebein was a navigation device developed from the Lorenz system
to help German bombers locate their targets at night. Thus, in order
to learn how the Knickebein worked, it should be helpful to discuss the
mechanism of the Lorenz system.
The Lorenz system had been in use in military and civil aircraft in several
countries since the mid-1930s to enable pilots to land at airfields at
night and in bad weather. It was essentially a system whereby two
direction-beam aerials were placed so that they radiated two wide beams of
a radio signal which overlapped along the center line of the airfield runway.
The aerials were automatically alternately switched to the transmitter so
that one radiated only morse dots and the other dashes. The spacing of the
dots and dashes was such that where the beams overlapped, the dots and
dashes joined to give a continuous note, known as the equi-signal, was very
narrow indeed and quite accurate enough for a pilot with a suitable receiver
to land on the exact center line of the runway. The frequencies used
internationally for this purpose were between 28 and 35mHz. The Lorenz
technique was simple but it called for a high standard of flying on the part
of the pilot, who had to be very proficient in the difficult art of
instrument-flying, that is flying without reference to a visual horizon.
Initially, while about fifteen to twenty miles away, the aircraft Lorenz
receiver would be tuned to the appropriate frequency; then the pilot, if his
aircraft was to the left of the airfield runway, would hear morse dots in
his earphones; he would then steer his aircraft to the right until the dots
became a steady note -- the equi-signal. At that point he would have to turn
left; if he did not turn far enough, the steady note would turn into dashes;
too much, and he would be flying into the dot zone again. Thus by making
small alterations left or right of his course, as indicated by the dots or
dashes, he would be able to keep in the equi-signal and thus be aligned with
the unseen runway. As he got nearer, the beam got narrower and more accurate
until, at touchdown, it was less than the width of the runway. The accuracy
of the system was such that a skilled beam pilot could detect a shift of a
hundredth of the equi-signal width.
The range of the Lorenz system was only 30 miles, but the Germans managed to
increase the range to 300 miles. The bombers, of course, would have to be
flying away from the beams rather than approaching, and this would mean it
would get less accurate with increasing range since the equi-signal zone
would get wider and wider. Therefore a second intersecting beam was sent
over the target to notify the bombardiers to drop the load. The most
pessimistic estimates of the accuracy of Knickebein beams would still enable
a large factory complex to be effectively attacked.
|Click on one of the thumbnails below to view the full picture.
||The aerials of the Knickebein transmitter at Cleves. About 100 feet high,
the structure was rotated round a circular track.
||A small later Knickebein transmitter in northern France, photographed by a British Agent.
||A captured EBL2 receiver. The five high-gain pentode valves gave the set unusual
sensitivity. This was the clue to its true function -- the reception of the Knickebein beams.
||A still from a Luftwaffe instructional film on the radio installation in a Ju 88.
||On the reverse side, the Lorenz sets, EBL1 and EBL2.
||A typical radio installation in a night bomber (Ju 88).
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