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 SIS Mk III  'Tinker Box' 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.  It was probably also the set-up installed by  engineers from SIS 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 later Auxiliary Units, based around the Home Guard,  that needed a simpler 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 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 it was inherently unsuited to clandestine warfare as  both the IN and OUT station had to be in fixed locations. Making the situation worse, until 1942 the IN Stations were based in surface huts attached to army HQs, making them vulnerable to dive-bombing. If the army HQ moved location then the connection to the OUT stations would be lost. The sets 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  The network was likely to be broken in the first days of invasion (when it was most needed) and this must have been realised.  It must therefore be considered if it survived simply on inertia (as other aspects of the Auxiliary Units, if it was part of a sacrificial deception scheme to convince the Gestapo that they had uncovered the real resistance network, or if it was retained more to assist the internal security monitoring of the population. 
Replica by Malcolm Atkin, with thanks  to  Richard Hankins 
photo © Susanne Atkin


Invented by Stanley Lewer in 1939 for short-range communication for barrage balloon control and between artillery and searchlight units.   It used the same VHF frequencies as the later TRD set and had a range of 15 miles.  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' 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 emphasises the difference between continental resistance organisations and the GHQ Auxiliary Units.


.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.
© 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 SDB was only incorporated into the system in 1943. Re-tuning the wireless sets to receive recreational programmes was strictly forbidden!
photo © Susanne Atkin

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