Electronic Weapons: Old, Reliable and Still Blinding

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March 9, 2018: In late 2017 Israel tested a new missile defense system for its Saar class corvettes. The new system uses a number of defensive systems based on software and sensors that rapidly identify and then deploys one or more countermeasures (flares, chaff or jamming signals). One of these countermeasures was quite visible when tested. This was the chaff filled rockets that rapidly put a cloud of radar blocking metal strips in front of the ship in the minute or two before the missile arrives. This is often sufficient to cause the missile to miss. Chaff was one of the many electronic countermeasures first developed during World War II. While electronic countermeasures and exotic stuff like lasers (to “blind” heat seeking missiles) get more publicity, something as simple, and visible, as chaff continued to be used ever since the 1940s.

Chaff made its first appearance during the Summer of 1943 when the use of electronic countermeasures seemed to have become a dominant factor in aerial warfare. The Allies introduced Window ("chaff") to jam German radar. Window was tinfoil strips, cut to the right length to cause German radar to see a "wall" of well, tinfoil strips. Bundles of it were tossed out of allied aircraft and this, in effect, created an electronic smoke screen behind which anything could be happening. The Allies began using separate groups of aircraft equipped with jammers and chaff to create deceptions and lure the German night fighters to them and away from the formations of bomber aircraft.

But the Germans fought back. In late 1943 they deployed the SN 2, an improved night fighter radar that was immune to Window and had a range of 400-6,000 meters. The use of chaff was a major blow to the German use of radar and they quickly responded to such challenges. In November, 1943, Germany began using Wurzlaus. This was a modified Wurzburg radar that could sometimes differentiate between stationary tinfoil clouds and nearby aircraft that were, of course, moving.

The Germans also modified their Wurzburg radar (the "Nurnburg" version) so that is gave an electronic sound to the operator, as well as the blip on the radar screen. After some training, an operator could use his ears to tell the difference between the radar signal coming back from a chaff cloud and one coming back from moving aircraft. Chaff, like so many other measures, was only a temporary advantage and soon was compromised by countermeasures. The Germans also used chaff, but with less success because the allies had many more interceptors and that limited the effectiveness of German chaff.

After World War II chaff continued to be used, but not as frequently or successfully and usually as an unexpected method for confusing radar. Electronic countermeasures became dominant although chaff was still around and often used with success when the enemy wasn’t expecting it. That use continues and the new Israeli ship defense system uses chaff (probably with different lengths of metal strips for different missile guidance system radars) as part of a larger number of countermeasures that that are quickly deployed by software and sensors that use speed and a constantly updated database of missile guidance systems to make missiles miss.

But sometimes chaff alone is still used in unanticipated ways. There was an example of this in 2003. To prevent Iraqi air forces from detecting and shooting at the 300 Tomahawk cruise missiles the U.S. Navy launched on the opening night of the war, a unique distraction was used. The Navy took five Firebee target UAVs and set them loose over Baghdad. Three of the Firebees were launched from a C-130 modified for the task. Two other Firebees were launched from Kuwait. The one ton Firebees were themselves to dispense chaff. The five Firebees, with an endurance of about an hour, flew back and forth over Baghdad until their fuel ran out, and then crashed. Iraqi air defenses were suitably shocked and awed and were caught by surprise when the cruise missiles that arrived soon after the Firebees went down. As always chaff will continue to be used successfully if it can be deployed when the enemy doesn’t expect it.

 


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