Nightfighting in World War Two
By Lee Brimmicombe-Wood Part 7-1. Confound and Destroy III: The Bomber Support Campaign THE STORY SO FAR: The RAF deploys a trio of countermeasures systems against the Germans. Mandrel jams the early warning radars; Tinsel jams communications and Window knocks out both Würzburg tracking radars and nightfighter radar. But every one of these measures is swiftly countered by the Germans.
Bomber Command's attack on Hamburg was a watershed in the radio war between the Allied bombers and the Reich defenders. From August 1943 to the end of the war, a see-saw struggle between the RAF and Luftwaffe was fought across the radio spectrum. Sometimes the RAF would have the ascendancy, only to see a superiority whittled away thanks to some new German countermeasure.
Sometimes the Germans turned the RAF's radio capabilities to their own advantage. One example of this radio ju-jitsu began with the introduction of an RAF system named 'Monica'. This was a tail warning radar that told the crew if a nightfighter was approaching from astern. Bomber crews did not entirely trust Monica, because in the densely-packed bomber stream it was prone to give false warnings. But they would have been even less impressed if they'd known the Germans had fitted a black box designated FuG 227 Flensburg
to their fighters. This homed in on the Monica pulses and was able to lead fighters directly to the bombers. Another German homing system was the FuG 350 Naxos-Z
which had been developed in response to the news that the British had deployed a microwave bombing and navigation radar named 'H2S' aboard their Pathfinder aircraft. The Naxos-Z
gave a bearing to H2S and though it was not accurate enough to pick out actual aircraft, it was good enough to direct fighters at the bomber stream. Flensburg
exploited the Achilles' Heel of RAF Bomber Command. Bomber streams, running all sorts of jammers and radar devices at full power, were penetrating German airspace broadcasting their whereabouts to the enemy. This made deceiving the Reich air defences all the more difficult. Indeed, it was to take the RAF another year to master the art of emissions control. PHOTO: In the nightfighting business wisps of antennae give away much about an aircraft and its function. This Me110G of Stab/NJG 4 mounts the standard FuG 202 Lichtenstein AI radar in its nose. But more interesting is the fixed Yagi antenna bent outwards from the wingtip. This is the receiver for the FuG 227 Flensburg. This would have been used as a contact aircraft, flying close enough to the bomber stream to track its emissions and broadcast a radio commentary on its course to nearby nightfighters. Later in the war, aircraft such as this would sport a plastic cockpit blister for the Naxos-Z's U-shaped rotating aerial.
The RAF were not without their own passive homing devices. Most notable of these was 'Serrate', which could detect the 490 MHz Lichtenstein
Air Intercept (AI) radar aboard German nightfighters. No. 141 Squadron under the legendary 'Bob' Braham trialled the device starting in June 1943. 141's intruder fighters were to claim 23 Luftwaffe nightfighters shot down, with nine falling to Braham's own guns. Despite this initial success, Serrate could not detect the metre-wave Lichtenstein SN-2
radar. As the Germans launched a crash program to equip themselves with SN-2 to proof their fighters against Window jamming (see Part 6), the number of Serrate contacts fell until by the Spring of 1944 they had almost disappeared.
The Germans successfully managed to keep SN-2 a secret from the British for a good many months. When an Me110G-4 equipped with SN-2 force-landed in Switzerland in April 1944 Hitler was prepared to order an SS commando raid, led by Otto Skorzeny, to parachute into the neutral country and destroy the machine. In the event, an international incident was forestalled by agreeing to sell the Swiss a squadron of Me109 fighters for a bargain price in exchange for blowing up the nightfighter and its radar. No sooner had Göring filed the cheque for the deal in his top pocket than the Swiss authorities discovered that the Nazis, in bad faith, had palmed them off with a dozen worn-out, almost unflyable fighters. However, the Swiss were to have the last laugh, winning substantial compensation in a court case brought against Messerschmitt and Daimler in 1951.
As a result of forthright action such as the Swiss deal, the SN-2 remained a mystery to the Allies until, by a remarkable stroke of luck, a Ju88 nightfighter landed at RAF Woodbridge in Suffolk on 13 July 1944. Its inexperienced pilot had flown a reciprocal compass course in error, heading west instead of east. The shocked crew were taken prisoner by an even more surprised Flight Sergeant armed only with a flare pistol and their aircraft taken into custody. The captured nightfighter had two systems previously unknown to British intelligence: SN-2 and Flensburg
. Tests done with Flensburg
soon proved how it could be used to home on the Monica radars of individual bombers. A horrified 'Bomber' Harris immediately ordered all Monica sets removed from bombers. When the boffins came to study the SN-2 they realized it worked on a frequency of 85 MHz (a wavelength around 3.2 metres), so standard 25 cm Window foil strips would not work against it. However, a long concertina strip around 160 cm long had been developed to fool sea search radars during the D-Day invasion and could be adapted for use against SN-2. Within ten days of the Ju88's capture, the new 'Type M' Window was being used to blind the SN-2 radars of the nightfighters. PHOTO: This Me110G-4 mounts the huge 'stag-antler' antennae of the metre-wave Lichtenstein SN-2. However, the small aerial cluster in the centre of the nose gives away that this aircraft is equipped with the SN-2b radar. These early SN-2 sets had a very large minimum range, and so a second radar set from a Lichtenstein C-1 was installed to cover this dead zone. The resulting installation was draggy and caused a loss of aircraft performance. Worse still, the Funker (or radar operator) was forced to use two separate radar sets simultaneously. The later SN-2c had a short enough minimum range that it could drop the C-1 set.
'Trade' for the RAF's intruders soon began to pick up again with the arrival of the Mark IV Serrate, which was tuned to the SN-2 frequencies, and a gadget named 'Perfectos' that sneakily activated the Identification Friend Foe (IFF) radio beacons aboard German fighters and obtained a bearing on them. RAF intruders, which began to upgrade from the Beaufighter to the superlative Mosquito, began to put the thumbscrews on the Luftwaffe nightfighter force. They also revived Monica, using it as bait to reel in unwary Germans who relied on the Flensburg
Such was the cat-and-mouse game of what was increasingly referred to in RAF circles as 'bomber support'--a combination of Radio Countermeasures, spoof operations and intruder escort missions designed to get the bombers through. Back at the end of 1943 it had become clear that bomber support was becoming so complex that a specialist organization was required for this work, and so RAF 100 Group (Bomber Support) was born, under the command of Edward Addison, who had been instrumental in the 'Battle of the Beams' jamming effort against the German Blitz. It was to begin its work in earnest in the summer and autumn of 1944.
100 Group was built from a variety of Fighter Command and Bomber Command units, including 'Ferret' electronic listeners, jamming squadrons and intruder fighters. One of their main tactics was to put up a Mandrel screen to blank out the early warning radars, running racetrack orbits over friendly territory to conceal aircraft movements behind the jamming. They also became adept at flying Window spoofs, using a small number of aircraft dropping carpets of Window to fake a bomber stream some 500 aircraft strong.