Josef Kammhuber

He organised the night fighting units into a chain known to the British as the Kammhuber Line, in which a series of radar stations with overlapping coverage. The stations were layered three deep from Denmark to the middle of France, each covering a zone about 32 km (20 mi) long (north-south) and 20 km (12 mi) wide (east-west). Each control centre was known as a Himmelbett (four-poster bed) zone, consisting of a Freya radar with a range of about 100 km (62 mi), a number of searchlights spread through the cell, and one primary and one backup night fighter assigned to the cell. RAF bombers flying into Germany or France would have to cross the line at some point and the radar would direct a searchlight to illuminate the aircraft. Once this had happened, other manually controlled searchlights would also pick up the aeroplane and the night fighter would be directed to intercept the illuminated bomber. Demands by Bürgermeisters in Germany led to the recall of the searchlights to the major cities.[2]

Slot Zeist, Kammhubers headquarters.[3]

Later versions of the Himmelbett added two Würzburg radars, with a range of about 30 km (19 mi). Unlike the early-warning Freya radar, Würzburgs were accurate (and complex) tracking radars. One would be locked onto the night fighter as soon as it entered the cell. After the Freya picked up a target the second Würzburg would lock onto it, thereby allowing controllers in the Himmelbett center to get continual readings on the positions of both aircraft, controlling them to a visual interception. To aid in this, a number of the night fighters were fitted with a short-range infrared device known as 'Spanner anlage' but these proved almost useless in practice.[4]

Kammhuber (left) and Helmut Lent in a Nazi propaganda photograph, France, 1942

Another tactic that proved effective was to send their own planes to England while the raids were taking off or landing. Radio operators listening to the RAF bomber frequencies were able to recognize the start of a raid and the raiding force of about 30 night fighters would be sent over the RAF airbases to shoot down the bombers as they took off or landed. By the beginning of October the night intruder force had claimed a hundred kills but on October 13, Hitler ordered the force sent to the Mediterranean, despite their success.

British intelligence soon discovered the nature of the Kammhuber Line and started studying ways to defeat it. RAF Bomber Command sent aircraft one at a time to force the defenses to be spread as far apart as possible, meaning that any one aircraft would have to deal with little concentrated flak. The Himmelbett centers were only dealing with perhaps one or two planes at a time, making their job much easier. At the urging of R. V. Jones, Bomber Command planned attacks against a target at a time, sending all of the bombers in a "bomber stream", carefully positioned to fly down the middle of a cell. The Himmelbett centers were faced with hundreds of bombers, countering with only a few aircraft of their own. So successful was this tactic that the success rate of the night fighters dropped almost to zero.

Kammhuber started looking for solutions, and the result was the two-prong concept of Wilde Sau ("wild boar") and Zahme Sau ("tame boar"). In the former, day fighters would be sent up and look for the enemy aircraft from the light of flares dropped from light bombers, searchlights set to a wide beam or illuminating lower clouds, or the fires on the ground below. The Wilde Sau force scored their most notable success during Operation Hydra (the British operation against the V-weapon centre), at Peenemünde on 17 August 1943. De Havilland Mosquito bombers had dropped target marker flares over Berlin and most of the night fighter force was sent there. When it was realized what was really happening, most of these aircraft were too far away and too slow to intercept the raid. However, the Focke-Wulf Fw 190s being flown by the Wilde Sau forces were able to reach them, and about 30 planes entered the third and last wave of the stream and shot down 29 of the 40 Avro Lancaster bombers lost on that raid.[5]

Zahme Sau envisioned freeing the night fighters (now equipped with radar for the final stages of the interception) from the Himmelbett cells and allowing them to attack on their own. This was not all that easy, given the capabilities of the current generation of radars, but newer systems being developed would greatly increase the detection range and angles. In this role the existing cells created as part of the original Kammhuber Line would be used primarily for early warning and vectoring the planes to the stream.[6]

At the same time Kammhuber continued to press for a new dedicated nightfighter design, eventually selecting the Heinkel He 219 Uhu after seeing it demonstrated in 1942. However Milch had decided to cancel the Uhu, and conflict arose between the two. As a result, in 1943 Kammhuber was transferred to Luftflotte 5 in Norway, in command of a handful of outdated planes. After the reorganization of the Luftwaffe in Scandinavia and the dissolution of Luftflotte 5, he became commanding general of the Luftwaffe in Norway (September–October 1944). In 1945 Kammhuber was re-appointed to command of the night fighters, at this point a largely ceremonial position considering the state of the Third Reich at that time.