Electronic Warfare & The Wesseling Raid
21/22 June 1944

The balance of power in night-fighting depended not only on aircraft but also on radar developments and counter-measures (as it has done ever since). In September 1941 R. V. Jones had warned Bomber Command that the Germans could trigger our IFF sets if these were left on - and so use the received signal to home in on the bombers. He was largely ignored. Worse, during 1942 crews took up the erroneous idea that pulses from their IFF sets could jam German searchlights. Bomber Command encouraged the idea on the grounds of morale. [Bombing 1939-45; Karl Hecks, p139-40]

In June 1942 IFF sets were fitted with a jamming switch which enabled them to transmit continuously, followed by the short-lived SHIVER set incorporating a true jammer.

TRE's MANDREL airborne radar noise jammer countered the German FREYA radars by radiating signals to swamp the normal return echo, thereby obliterating formation size and range information.

TINSEL and its predecessor GASTON provided airborne jamming of German defence R/T, disrupting voice communications between ground control stations and nightfighter crews. TINSEL used a microphone mounted in an engine nacelle, linked to a radio transmitter. A German speaking crewman used the aircraft's normal radio receiver to search for fighter control R/T, then tuned TINSEL's transmitter to broadcast the engine noise on the same frequency.

MONICA, the RAF's tail warning radar, entered service in early 1943. Tail mounted and pointing rearwards, it provided audible bleeps as a warning of an aircraft approaching from the rear. However, a German night fighter could 'hide' among the bleeps generated by other bombers in the stream.

By March 1943 the Germans had examples of MONICA from shot-down aircraft and it became dangerous to use once they equipped their nightfighters to track MONICA emissions. Although partly superseded by FISHPOND, MONICA remained in use until mid 1944. According to Bill Gunston, by that time MONICA had been responsible for more bomber losses than any other single device in the War. [Night Fighters - A Development and Combat History; Bill Gunston, p11]

WINDOW had been tested by both the Germans (DUPPEL) and the British but was not used for fear of being unable to provide countermeasures. The Japanese were the first to use it operationally, in night raids on GUADALCANAL in May 1943 (GIMAN-SHI - 'deceiving paper'), but apparently neither the Germans nor the British were informed about this by their respective allies.

WINDOW was first used operationally by the RAF in the July 23rd raid on HAMBURG. It consisted of foil strips 30cm x 1.5 cm, stiffened by backing paper and lamp blacked so as not to show up in the searchlight beams. Bundles were hand dropped down the flare chutes at one per minute, to burst and drift down, taking two hours or more. RAF losses were down to 1.5% from 6%, and the blinding of the WURZBURG radars was complete.

The earlier radar set fitted to German fighters had been the LICHTENSTEIN, which was efficient but badly jammed by WINDOW and was being homed in on by the SERRATE sets in the Mosquitoes of 100 Group. A new German radar - SN2 - was quickly produced and fitted to night -fighters in the early months of 1944: it was hardly affected by WINDOW and could pick up a bomber at four miles range against LICHTENSTEIN's two miles. Until SN2 was identified, the Mosquito SERRATE sets were not adjusted to the new impulse frequencies, giving a temporary advantage to the defenders.

Again, RV Jones (who Churchill called 'the man who broke the bloody beams') commented “Perhaps we did not stress the importance of SN2 sufficiently. It showed up only rarely in the ENIGMA traffic of February 1944: this may be explained by the fact that at the beginning of that month only 90 out of 480 night fighters were completely fitted with it. But as it was given first to the best night fighting crews, its effect was greater than the simple numerical proportion.”

“And although on 6th March 1944 I had set the establishment of the SN2 wavelength for countermeasures as one of the two most urgent problems, and even though some weeks before we had correctly that this wavelength was 3-4 metres, our listening searches failed to detect it. Proof only came when American camera guns caught the Ju88s and Me110s fitted with SN2’s ponderous aerials - these photos came to us in May 1944. Even then its transmissions were not heard until after a Ju88 fitted with SN2 landed in error and intact at Woodbridge in Suffolk on July 13th 1944.” [Most Secret War - British Scientific Intelligence 1939-45; RV Jones, p392]

This brand new aircraft, a Ju88G-1 of 7/NJG2, proved to be equipped not only with SN2, but also NAXOS-Z and FLENSBURG, a passive homing device tuned to MONICA. [The Avro Lancaster, Francis K Mason, p191-2]

Switch off
According to Gunston (ibid) “British courage, technical expertise and capacity for hard work has never been manifest more abundantly then in the stirring final year of the night battle over Germany. Its cumulative effect on the morale of the Luftwaffe, from Goering down to the lowliest hangar sweeper, was enormous. The entire NJG force gradually came to feel the British were simply cleverer or quicker off the mark and thus were perpetually one jump ahead.”

“But in fact this was not true. For a whole year, every conceivable method had been tried to find out the frequency of LICHTENSTEIN, SN-2 and details of NAXOS-Z and FLENSBURG, without success. No trace could be found of a new nightfighter radar emission (so that a fair conclusion would have been that SN-2 emitted signals similar to those some previous set, which in fact happened to be the advanced forms of FREYA). The other sensors emitted no radiation at all and the numerous nightfighters shot down by Mosquitoes all fell on German soil.”

“In January 1944, monitoring of German R/T showed that they were tracking bomber streams at ranges of up to 350km, far beyond normal ground radar range. Despite the likelihood that our IFF sets were being triggered, no action was taken.” [Bombing 1939-45; Karl Hecks, p254]

“Prospects were extremely discouraging (Gunston, ibid). Then before dawn on July 13th 1944, a single aircraft orbited RAF Woodbridge, Suffolk; got a green and landed. The crew bus ambled out to collect what was expected to be the pilot and observer from a Mosquito. Instead it collected three men in Luftwaffe gear. Having set the reciprocal course by mistake, they had brought one of the latest Ju 88G nightfighters.”

“In a matter of hours Bomber Command had set in motion actions which were to remove the last advantages enjoyed by the German nightfighters. It learned all about SN-2, checked that it was unaffected by standard WINDOW, but found that its vision was seriously impaired by a special long concertina form WINDOW that Bomber Command had used during the invasion to simulate a non -existent fleet of surface ships.”

“Design was begun on a crash basis on SERRATE IV, to home on to the German radar - and PIPECRACK to jam it. Another cunning device PERFECTOS harping still further on the cigar theme, was carried by the intruder Mosquitoes to interrogate the latest Luftwaffe IFF sets and give the bearing and range of the replies! But perhaps the most urgently needed result of all came us soon as the Ju 88's almost empty tanks were refilled.”

“Wing Commander Derek Jackson, one of the Scientific Officers engaged on the development of radar and radio countermeasures, undertook test flights at Farnborough with the Ju88 G which had landed at Woodbridge.” [The Avro Lancaster, Francis K Mason, p191-2]

“He began by trying the passive homer (FLENSBURG) against the MONICA radar of a single Lancaster and found it gave clear bearings out to a range of at least 130 miles.”

“He then tried it against five Lancasters flying in a loose gaggle and found that he could home the big nightfighter immediately on to any one of the five. Still Bomber Command argued, so at the end of August 1944 he managed the final evaluation against a 'bomber stream' of 71 Lancasters orbiting between Cambridge and Gloucester. Far from being smothered or confused, the FLENSBURG continued to give crystal clear indication of the exact positions of the nearest bombers.”

“Clearly, this one aid alone could guide a night fighter crew straight to any bomber using its tail warning radar. At once Bert Harris ordered the MONICA sets not to be switched on and to have their frequency changed at the earliest opportunity. At last the RAF bombers stopped telling the dreaded nightfighters where they were.”

In Mason's account, Harris ordered every MONICA set to be removed from Lancasters and taken out of service immediately. Nor was the purpose of NAXOS-Z lost on the British scientists. The use of H2S, AIRBORNE CIGAR, MANDREL and TINSEL was expressly forbidden until aircraft had reached enemy airspace. Even IFF was henceforth only to be used in the direst emergency.

Of course MONICA was not an entirely misguided device (Gunston, ibid), any more than was H2S. Both did achieve their objective of providing information for the bomber crew and in a very small minority of cases - especially those in which the fighter used forward firing armament and thus closed from dead astern - the bomber crew detected the fighter's presence in time to do something about it.

By far the best thing was to cork-screw: to open the throttle wide and fly a very large horizontal corkscrew path that kept the bomber something like 500 feet away from the original straight and level trajectory. It was a strenuous, sick-making manoeuvre, best performed without bombs (though from 1942 onwards it was extremely rare for an RAF bomber to jettison its load short of a target unless a nightfighter had shown itself to be skilled and aggressive).

“In daytime a corkscrew would not seriously inconvenience an experienced fighter pilot, but at night it was a different matter. The greatest Luftwaffe experte of all, Major Heinz-Wolfgang Schnaufer, gained three of his 121 confirmed night victories with SCHR4GE MUSIK cannon when he was actually formatting with a corkscrewing bomber; but he also had some fruitless encounters because of this manoeuvre and once followed a corkscrewing Lancaster for 45 minutes without being able to get it in his sights (he vowed he would never again waste time in this way; there would always be other, easier pickings).”

“All the formidable developments that the Germans made could be largely countered by switching off H2S and MONICA, keeping a sharp lookout and having the guts to corkscrew better than the average Luftwaffe fighter. The night battle over Germany was one of increasingly clever technology, but courage and skill still played a large part and the element of sheer chance also assumed frighteningly large proportions.”

“Heavies would carefully fly low, or high, to escape the worst of the flak - and be hit by a shell incorrectly fused. They would turn every 15 seconds or so when running through the most intense radar directed flak - and run into a badly aimed shot. They would keep their eyes peeled for a night fighter but be physically unable to keep lookout below, where the fighter was most likely to be. Others would keep such a jittery lookout that when they saw another Lancaster or Halifax loom close, they shot it down. Others lost out through collisions or from a rain of friendly bombs from above. Over 55,000 aircrew failed to return.”

“Yet it was far from being a one sided battle. From mid 1943, no Luftwaffe nightfighter pilot ever felt safe in his own night sky and far more were killed in crashes (often caused by fear of the omnipotent Mosquito) than in combat. Many were shot down by their own flak and once PERFECTOS had made them switch off their IFF, this happened frequently.”
“In the end, along with the rest of the Luftwaffe, the remnants of the once proud and formidable nightfighter wings just ground to a halt. Their airfields were blasted, their organisation was in chaos and worst of all, aviation fuel had become an almost non-existent commodity. This was because of the destruction of the German oil refineries, synthetic oil processing plant and storage tanks by the bombers that got through.”

last updated 26 May 2005