Description
The first version of the Line consisted of a series of radar stations with overlapping coverage, layered three deep from Denmark to the middle of France, each covering a zone about 32 km long (north-south) and 20 km wide (east-west). Each control centre was known as a Himmelbett (canopy bed) zone, consisting of a Freya radar with a range of about 100 km, a "master searchlight" directed by the radar, and a number of manually directed searchlights spread through the cell. Each cell was also assigned one primary and one backup night fighter. The fighter used was usually a Dornier Do 17Z-10, Junkers Ju 88C or Messerschmitt Bf 110. This technique of Ground-controlled interception (GCI) was preceded by the use of single-engined non radar-equipped BF 109s guided to the attacking bombers by the illumination of searchlights, termed; Helle Nachtjagd - illuminated night fighting.
RAF bombers flying into Germany or France had to cross the line at some point, at which time the Freya radar operators directed the master searchlight to illuminate the plane. Once this had happened other manually controlled searchlights also picked up the plane, and the night fighters were directed to intercept the illuminated bomber. Demands by the Bürgermeisters in Germany led to the recall of the searchlights to the major cities, which undermined this system.
Later versions of the Himmelbett added two Würzburg radars, with a range of about 30 km. Unlike the early-warning Freya, Würzburg's were accurate (and complex) tracking radars. One was locked onto the night fighter as soon as it entered the cell and as soon as the Freya picked up a target the second Würzburg locked onto it. All position reports were sent to the Himmelbett control centre thereby allowing controllers in the Himmelbett centre to get continual readings of the positions of both planes.
A Jägerleitoffizier directed the German night-fighter to a visual interception with the RAF bomber using radio. Operations were manually coordinated using an "Auswertetisch" (the precursor of a "Seeburg" table). To aid interception a number of the night fighters were fitted with a short-range infrared device known as Spanner but these proved almost useless. Later the short-range Lichtenstein radar was added to the aircraft, allowing them to detect aircraft once the operators had directed them into the area, making searchlights largely redundant. The battle stations were known as "Kammhuber's opera houses" and procedures developed in 1942 were used until the end of the war.
Read more about this topic: Kammhuber Line
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