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1940 mk 5 transmitter.jpg


Clandestine wireless sets were at an early stage of development  in 1940.  SIS had already begun to distribute some very crude long-range clandestine sets in Poland, Scandinavia, Netherlands  and France before the Nazi occupation.  These were also used by their Section VII network and used morse code transmissions.  The Special Duties Branch of the Auxiliary Units only used short-range  sets using voice transmissions.  No sets were immune from detection and the work of the wireless operator was the most dangerous  job in any resistance organisation.  At the end of the Second World War, in order to prevent future illicit use, SIS made determined efforts to destroy as many clandestine sets as they could find.  The destruction of the TRD sets was more complete than the types in use on the continent - simply because they were easier to recover from within the UK.

HRO receiver and MkIII transmitter


This was the standard long-range wireless combination installed in SIS Stations around the world from 1940 and was also the main equipment of the SIS Special Communications Units and intercept stations.  Despite its bulk, it was also provided to some resistance forces.  This was probably also the set-up installed by SIS engineers in the hides of XII Corps Observation Unit in June 1940.  If so, this highlights the difference between an organisation based on the army, able to use morse code, and the Auxiliary Units, based around the Home Guard and civilians. The latter needed a more simple set (the TRD) using voice transmission.
Replica of Mk III transmitter by Malcolm Atkin.                

photo © Susanne Atkin

TRD set

Developed by John Hills for the Special Duties Branch of the Auxiliary Units in late 1940,  based on  research by  Cambridge University,   SIS Section D and Stanley Lewer (inventor of the  WS17 set).  It was short range VHF set (with a normal range of 30 - 60 miles) that used voice transmission (and therefore required minimal training - allowing a civilian network to be quickly established). It was not the super-secret set of legend and although its signal could only be deciphered by another TRD set, the signal was not in itself undetectable. Instead, the TRD relied for security on its use of rarely-used VHF frequencies and a very directional aerial. The latter meant the TRD set was inherently unsuited to clandestine warfare as  both the IN and OUT station had to be in fixed locations. 

Until 1942 the IN Stations were based in surface huts attached to army HQs, making them vulnerable to dive-bombing. If the army HQ had to move location then the connection to the OUT stations would be lost and the network put out of action.  The sets and aerials also required  regular maintenance by the Royal Signals personnel whose services would have been unavailable after invasion. See also Wireless for Warriors Vol.4, Supplement, Chapter 111-1  

Although an undoubted improvement on the initial reliance on 'runners', the Special Duties wireless network was likely to be broken in the first days of invasion - as soon as the Army HQs moved location in what experience suggested would be  a fast-moving campaign. As the lesson of Blitzkrieg was that there was unlikely to be a continuous front, the value of the Special Duties network was essentially as an early warning alarm to report the new arrival of enemy forces in an area (thereby another facet of  the role performed by the army 'Phantom' Units and the Royal Observer Corps). Of limited practical value beyond this, the network may also have been seen as a useful deception scheme to convince the Gestapo, once they penetrated the network, that they had uncovered the real Resistance. Thereafter the main practical role of the Special Duties Branch (as with the SIS Section VII resistance), may have been to assist MI5 and the Field Security Sections in  the internal security eavesdropping on the civilian population and troops. 
Replica by Malcolm Atkin, with thanks  to  Richard Hankins 
photo © Susanne Atkin

Replica of TRD wireless set
WW2 WS17 wireless set


Invented by Stanley Lewer in 1939 for short-range communication for barrage balloon control and between  artillery and searchlight units in fixed locations.   It used the same VHF frequencies as the later TRD set and had a range of 15 miles, suffering also from the same limitations of reliance eon a directional aerial..  It was a set that the developer of the Auxiliary Units wireless sets, John Hills, would certainly have been aware of as a possible model.

The set was extremely noisy - enough to cause problems with low flying aircraft!  Nonetheless, by 1944 (although  out-of-date even at the time of issue)  the WS17 comprised 40% of the wireless sets used by the Special Duties Branch of the Auxiliary Units. 
photo © Susanne Atkin



The first 'portable' clandestine wireless set, designed to be carried in a large suitcase.  Widely used on the continent from 1941, it did become notorious for the number of agents arrested whilst carrying it - betrayed simply by the unusualy heavy weight of the suitcase (15k). The reliance on such sets using morse code, emphasises the difference between continental resistance organisations and the SIS networks in Ireland and Britain,  and the GHQ Auxiliary Units.

Replica by Malcolm Atkin

photo © Susanne Atkin

SIS MkV wireless set
WW2 Paraset wireless set


.An improvement on the Mk V, introduced in 1941 and able to be carried in a small attache case.  This set best fits the description of the set used by the Eastbourne cell of the Section VII network.  It was also used as a back-up wireless set by the Special Communications Units of SIS.  Widely used on the continent by SIS and SOE networks. Some supposed SDB wireless operators are described as using a wireless set concealed in a 'briefcase' and this suggests they might actually have been Section VII agents using a Paraset.
© IWM (COM547)


Murphy B81 Wireless Set
Not exactly clandestine - but issued to the Special Duties Branch of the Auxiliary Units from 1943.  This 1939 battery-powered wireless set was widely issued to the military in order to receive the BEETLE emergency broadcasts.  These messages could be received on any domestic wireless set tuned to specific long-band frequencies. The system overcame the shortage of army wireless sets in 1940  and short-circuited lengthy signals distribution systems.  The first priority was to beach defence units but this was extended to Home Guard anti-tank islands in July 1941.  The Special Duties Branch  was only incorporated into the system in 1943. Re-tuning the wireless sets to receive recreational programmes was strictly forbidden!
photo © Susanne Atkin

Murphy B81 wireless set
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