Radar and the Air War – Part 7 – by John Heys G3BDQ

A Personal View, by John Heys G3BDQ.

Part 7 – The Nachtjagd     (German Night Fighter Force)

It was springtime in 1943; the Squadron had returned from its assistance to Coastal Command and base in Chivenor, Devon.  It had recently converted from Whitleys to Halifaxes and from December 1942 had resumed bombing operations.  About 95% of the squadron’s personnel (the remainder were kept on essential duties) were assembled for a ‘Special Inspection’ with everyone trying to guess who our visitor would be.  We were in lines and dolled up in our ‘best blue’ uniforms with, a rare treat this, our boots polished!
An elderly gentleman processed down the lines.  He wore an odd mixture of RAF uniform and civilian dress and had a walking stick. It was the doyen founder and ‘father’ of the RAF in 1918, Lord (1st Baron) Hugh Montague Trenchard who remained upright and sprightly despite his seventy years. Bomber Command losses had escalated dramatically through April and May of 1943 with the two months’ losses rising to 487 aircraft.  The old warrior had been dragged out of retirement to visit the active squadrons and perhaps bolster the sagging morale of many crews.

This sudden increase in losses was largely brought about by the increased numbers of aircraft involved in operations over Germany and also a rapid growth in the effectiveness of the Nachtjagd and an improved deployment of the enemy Radar-controlled searchlights and Flak batteries.  The German night fighters did not venture across our coastlines and for a considerable time Bomber Command had no knowledge of the introduction of the AI (Air Interception) devices in the Luftwaffe’s twin-engined Junkers 99, Messerschmitt Bf110E and Heinkel 219s. AI equipment was code-named Lichtenstein BC which had been first used in August 1940 against a force of 44 Wellingtons that were attacking Hamburg.  On this occasion Lichtenstein had achieved its first victory, but it was during 1942 that this new equipment was installed in most of the enemy night fighter aircraft.

The Lichtenstein BC radars were operated by a Bordfunker (Radio Operator) who also worked the radio communications equipment.  In flight the pilot or his Funker referred to the AI radar as ‘Emil-Emil’ to confuse any British radio eavesdroppers whenever they spoke to their ground control stations.

The bulky Lichtenstein beam antennas that protruded at the nose of the fighters were referred to as Hirschgeweih or Stag’s Antlers.

These antennas limited the top speed of the equipped fighters but it was a small price to pay for the effective performance of the radar.

The Lichtenstein BC (Mk. 1) operator had three small CRT tube faces to study.The left hand tube was his long range display and it used a circular time base. The centre screen showed whether the target was above  or below the fighter and the right hand screen showed whether the target was to port of to starboard. The Funker used the display to direct his pilot to a position astern of and slightly below the bomber – a position most likely to allow a successful attack. This fist type of Lichtenstein was eventually rendered almost useless by the jamming caused by ‘Window’, (also called ‘Chaff’) that was dropped in huge quantities by our bombers on and after July 24th 1943; but soon the original radar was replaced by Lichtenstein SN-2 which was unaffected by the metallized paper strips.

The earlier Lichtenstein operated on a wavelength of 61cms which was close to the 53.5cms wavelength of the Wurtzburg ground radars against which Window had been prepared.

In July 1943 Generalfeldmarschall Erhard Milch, the Director-General of Equipment (Air) wrote to Dr Rottgerde of the electronics firm Telefunken and outlined his thoughts on the future development of night fighting. This resulted in the development of the new Mk II Lichtenstein SN-2 which also had a wide angle version designated Lichtenstein C-1 Weitwinkel.

This model had a switched frequency range and could avoid most jamming signals.  It could operate on the frequencies of 72, 81 or 91 MHz instead of the fixed frequency of 54 MHz used on the Mk1 sets. This new Lichtenstein SN-2 employed just two cathode ray tubes, one for bearing and one for height and had a range of up to six kilometres. These new SN-2 sets were fitted into night fighters during September 1943, and by the end of that month 2000 radars had been fitted. The SN-2 antenna system comprised 2 over 2 element yagis on both the port and starboard sides of the aircraft nose (altogether four two element vertically polarised beams).

A British Breakthrough

At 1530 hrs on the 9th May 1943 a JU88 took off from its base at Kristansand in Norway, ostensibly to make a test flight. Its pilot Oberleutnant Heinrich Schmitt, his Funker Overfledwebel Paul Rosenberger and a flight mechanic Oberfeldwebel Erich Kantwill had already planned a flight to the British Isles. A fake SOS was sent back to their base saying that an engine was on fire and that they were ditching into the sea. They flew on in their Lichtenstein equipped JU88 R-1 and landed at RAF Station Dyce near Aberdeen. This event delivered a complete and working German AI radar into our hands and it was a Godsend to the British scientists leading to the development of an airborne device code-named ‘Serrate’ that could detect Lichtenstein signals at a range of up to 80 kilometres when directly facing the nose of the enemy aircraft. This would allow a Beaufighter aircraft to home on to enemy fighters.

The new SN-2 Lichtenstein radars used a display different from that used on the earlier Mk1 sets. It used just two CRT displays and was immune to Window by the employment of a clever circuit that could, by checking for the Doppler effect, distinguish between the echoes from a British  bomber and the multiple returns from the myriad strips of window. The earlier Lichtenstein  radars could pick up an aircraft from two to three kilometres away whereas the new SN-2 could detect and home on to targets at a distance of six kilometres.

Initially the German air defences used a system that they called Zahme Sau (tame boar) to attack the British bomber streams.  The ‘tame boars’ were the night fighters who operated under the control of ground based instructions. There were different sectors over Germany and the Low Countries each having a control centre which received intelligence from the ground radars and then directed individual fighter aircraft to targets that were often helplessly caught in searchlight beams.  As the bomber stream progressed towards its target it entered new defence ‘boxes’ and different night fighter groups. A growing problem faced by the night fighters was the jamming of the radio instructions coming from their ground control. Several Nachtjagd aces pressed for changes to this ‘box’ system and the tactic adopted became know as Wilde Sau (wild boar) which gave free rein to the fighter pilots who could then just use their SN-2 radars to find and hunt down unfortunate individual British bombers. This new technique proved successful and it was continued right up to the end of the war. The worst month of operations over occupied territory for the RAF was June 1944 when 293 bombers were reported missing. Such a high loss rate could not have been sustained, for the missing aircraft could not have been replaced during the following month.

The ‘Killer Music’.

The Luftwaffe had some brilliant night fighter pilots, and clearly their top Ace was Heinz Wolfgang Schaufer who was officially credited with 121 victories. Each of his ‘kills’ is fully documented and amongst them were two Halifaxes from No. 77 my own squadron.
Until after the War the RAF did not know why the Nachtjagd  had been so effective.  But examination of the remaining German aircraft in the days just after the cessation of hostilities revealed a secret weapon.  This was know as Shrage Musik by the enemy pilots, two words which mean ‘Slanting Music.’ It was a weapon which employed rearward sloping cannon or machine gun barrels positioned on top of the fighter fuselage and just to the rear of the cockpit. The Lancaster and Halifax bombers shared a blind spot below and just forward of centre of the aircraft.  An SN-2 Lichtenstein equipped German fighter was able to come up from the rear to a position beneath its target, and it was soon learned by the Luftwaffe pilots that the ideal placing was just below the wing roots of the bombers. Here the petrol tanks in the wings were located and a short blast of cannon or machine gun fire aimed there would result in an almost instantaneous explosion and fire or perhaps a few seconds of fire before the wing was blown off.  Many crews often died without knowing the reason for the catastrophe.

Severe fuel shortages in 1945 kept most of the Nachjagd force grounded and RAF bomber losses rapidly fell. Through April and May of that year only 54 aircraft were lost to enemy action. We were fortunate that the new German Jet fighters were few in number at that time and that Allied night and daylight bombing had seriously limited supplies of aviation fuel to the German fighter squadrons.

John Heys (G3BDQ) – Vital Spark January 2008.

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