Archive: Oct 2015

  1. Innovative Drone Defense Systems are 70 years old

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    Department 13 is developing an innovative drone defense system, to deal with the security challenges that consumer/COTS drone systems pose to the modern world. Daily media reports highlight the challenges that UAVs provide, describing them as some form of new menace.   But at D13 we are acutely aware that we aren’t the first to take on a challenge of this kind. Although the technologies we are applying are new and innovative, the history of countering UAVs goes back at least 70 years.  This is the story of that earlier technological development, a technological battle that took place at the height of WW2, and which demanded innovative technology to save lives.

    In about 1943 the German Luftwaffe started to deploy a guided bomb, commonly called the “Fritz X” that dropped from about 13 – 18,000 ft and could then be guided towards its target, about three miles away.  The system used a “MCLOS” system with the operator in the attacking aircraft tracking both the bomb and the target and guiding the bomb.


    A Fritz X being released in a trial


    Accuracy varied but it is clear the system offered some significant opportunities to attacking aircraft, because it takes a bomb about 30 seconds to fall that sort of height, and target ships were maneuvering at high speed.  Admittedly there were downsides too, such as the vulnerability of the aircraft during the attack.  The system included a transmitter on the aircraft, controlled by an operator using a joy stick ( a clear precursor to a modern game controller)  and a receiver in the bomb which controlled vanes in the bomb’s tail unit. This captured German film, released by the US in 1946 is fascinating showing the simplicity and modern design of aspects of the system, as well as the use of a training system. (It’s a little confusing in the middle, but the demo of the gyro stabilisation of the munition is fascinating in its simplicity.)

    Later in the war a “cruise missile”, The Henschel Hs-293 glide bomb was introduced, giving greater stand-off range of about 7 miles. This is clearly what we would call today a UAV. It used the same radio control system as the earlier guided bomb.


    Hs- 293 being released.

    It is clear that early on the allies regarded the Fritz X and the subsequent Hs 293 as a significant new threat – battleships were lost and significant casualties were caused. Contemporary reports describe the surprise of naval forces who watched Luftwaffe aircraft drop large bombs several miles away but then saw the bombs head towards them. But by late 1944 the threat of these weapons had all but disappeared. This was largely due to a very effective package of technical intelligence operations which permitted effective electronic counter-measures (jammers) to be deployed. In addition, the Allies were fortunate to get other intelligence on the system from captured prisoners of war.

    The intelligence activities took two forms.  Firstly, using radio receivers to scan the airwaves to understand the control mechanism and define the frequencies and signals being transmitted from the attacking aircraft.  The British RAF set up a special unit called “Y-Service” that deployed in Naval ships and who manned the receivers to analyze the signals. A ship’s captain, on a vessel they served on, described them as “boffins with pale faces, thick glasses and a special radio set”. (Possibly the first ever report of “the geek”!).  These techies eventually identified that the signals were being transmitted on a particular frequency (it turned out eventually to be 48 – 50 Mhz).  They worked out that the base frequency was then added to by an additional frequency to control the munition – with the receiver having four filters to respond to the specific signal of up, down, right or left.  The observing scientists were able to match significant changes in the bombs movement (filmed by a cameraman in the team) with changes in the signal.

    The second TECHINT operation involved exploiting captured receivers (from bombs that failed to detonate) or transmitters from shot down or seized aircraft.  Obtaining captured receivers was tricky because the Germans were wary of such exploitation and fitted an independent self-destruct mechanism on the receiver, separate from the bomb fuze.   A key part of the response was the seizure of technical components at an Italian airfield used by the Germans in Foggia, Italy, in September 1943. These components were returned to both UK and US for rapid evaluation. On abandoning a series of aircraft as the Allies approached Foggia, the Germans had individually sabotaged a number of their own aircraft with the system aboard to prevent Allied exploitation- but (in haste) not consistently in the way they had done it, so from a number of components a working system could be built and exploited.

    A recovered control system.


    The counter measures used a couple of techniques . The first technique was the age old “power battle” – transmit powerfully enough on the same frequencies and the receiver will be overwhelmed and listen to the most powerful signal.  One problem was that the weapon had a choice of about 20 base frequencies, and anyway when the counter-measures were first under development there was no knowledge of the narrow(ish) band of 48- 50 Mhz they were operating on.  So the system had to include components to “receive” and identify the signal and then retransmit on the same frequency.   The scientists of the time faced a real challenge in building receivers that could cover that significant range of frequencies.   Initial jammer systems were focused by guesswork alone at 17- 20Mhz, missing the threat band completely. After the Foggia seizures had focused the frequency band to 48- 50Mhz a new set of jammers were produced. The frequency had been confirmed by US Signals intelligence deployed in two specially equipped vessels, in November 1943.

    The second US “crash program” to prepare jammers focused on the correct frequency began immediately, and were rushed to the theater as each was completed. The transmitter components issued a powerful 500W signal, via twin antennas, one on either side of the ship in which it was deployed. This second jammer system still had a key weakness – it had to be manually tuned to the specific frequency within the 48-50Mhz band that any particular incoming munition was using. And only one munition could be jammed by one jammer.  So this system required multiple systems in the event of an attack my more than one UAV, required a “man-in-the-loop” on each system to dial in the appropriate frequency once detected on a separate system, and coordination of all those discrete actions and systems.

    The British adopted a different tack, led by a twenty-one-year-old electrical engineer, David Silvester. They developed a system that would operate across the “threat band”. Their solution is  a bit technical to explain in a short blog but modern electronic counter-measure specialists will be intrigued to know that they used the 3Mhz intermediate frequency of the “super-het” component in the receivers in an “elegant” manner thus allowing a paired system to jam across the threat frequency by exploiting the local oscillator frequency.   Thus, a single system could jam multiple UAVs.  It’s worthy of note that superheterodyne receivers were first developed by a US scientist in WW1 – for use in radio intercepting equipment, by a signals intelligence unit.  The UK jammer was known as the “Type 650” jammer and was widely deployed from early 1944.

    Those wishing more detail should read “Warriors and Wizards”, an excellent technical account of the threat and Allied response.

    Today, cheap and widely-available UAVs are posing significant challenges.  Both UAV technology and the technology to defeat them have moved on, but the D13 team are immensely respectful of the technological innovation shown by pioneering scientists in the heat of war, 70 years ago, that laid the foundation of electronic warfare in this field.

    Roger Davies, BD Director, D13

  2. Jonathan Hunter – Chairman and CEO

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    • Degree in Criminal Justice with a graduate MBA in Technology Management
    • Former advisor to the National Academy of Science on defense technology applications
    • Over 25 years experience in leadership positions within the US Military and Government Advisory Committees