Electronic Warfare (Measure-Counter Measure)

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.

In 1937 a British research scientist, R.V. Jones, first noticed that a strip of aluminium foil drifting through the air produces a blip on radar screens. 2,000 of these strips, 11/2 ft high and 1 inch wide, shows up on radar screens very similar to a British heavy bomber. In the summer of 1941 a RAF Wellington bomber fitted with special radio aerials (antenna whips) found it received a lot of attention by German gunners even when it was flying among other planes. It was deduced that the radio aerials created a larger radar echo of the bomber than would be the case otherwise, thereby drawing more enemy fire. During the next air raid this bomber participated in, against Benghazi in Libya, the crew dropped packets of aluminium strips 18 inches long and 1.5 inches wide (the size of the special aerials) but no change was observed. One more time the aluminium strips were used but with no useful results the whole idea was abandoned.

A year later and after many experiments it was found that a bundle of 240 aluminium strips produced a radar echo similar to a RAF Blenheim bomber. Ten such bundles released over a mile made it nearly impossible for radar to pick out the real bomber‘s echo. First used operationally in a series of four major raids by bomber Command against Hamburg July 24 – August 2, 1943. On the first night alone 92 million strips of Window were released (about 40 tons) from 746 RAF bombers. The German radar operators were totally confused because the Window cloud showed up on their screens as thousands of aircraft. Accurate pinpointing of the invading bombers was therefore impossible so that, on that night, the German night defences were rendered completely ineffective. The new weapon spelled the end of the Himmelbett system because, with both the flak and night fighter arms denied radar back-up they had to rely upon random pick-ups by the similarly handicapped searchlights successfully confusing the German defenses. From this point forward Window was used on every air raid and in many of the numerous spoofing raids to deceive the German defenses.

Window was aluminium foil stiffened with a black paper backing and cut into strips 30 cm long and 1.5 cm in width. The silvery side was coated with lampblack, a fine soot collected from incompletely burned creosote or kerosene, so the clouds of Window would not show up in the glare of search lights. At first window was released from the aircraft by any convenient opening but soon each Lancaster was fitted with a louvered box structure on the lower starboard side of the nose. From here Window was released by the Flight Engineer or the bombs Aimer.

The AAF called window “chaff” because of the way it resembled wheat chaff in the wind. First use by 8th Air Force was in December of 1943 and for the 15th Air Force March of 1944.

By 1944 every AAF bomber in the lead wing carried 144 packages of chaff. These were dropped at four second intervals, so each plane could lay a chaff lane or “corridor” 20 miles long.

Mandrel

The Germans’ Freya early warning radars were reinforced by the introduction of the Wassermann (Aquarius) and Mammut (Mammoth) long distance radars which could plot bombers above the radar ‘horizon’ as far north as Norfolk and Suffolk, but these could be jammed by the British airborne Mandrel device.

To counter Freya, the British used equipment called ‘Moonshine’. Carried by Boulton Paul Defiant aircraft of the Special Duties Flight (later No. 515 Squadron RAF), a single set retransmitted a portion of the Freya signal amplifying the apparent return. Eight planes with ‘Moonshine’ could mimic a force of 100 bombers

Bombers could also detect when they were being monitored by the German Würzburg gun-laying radar with a device called Boozer.

Measure Counter-Measure