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Post-War Echo of Aux Unit Hides

Much of the modern interest in the GHQ Auxiliary Units focuses on the romanticised mystique of their buried Operational Bases (OBs) - a term later preferred by the organisation rather than ‘Hides’ as originally used by Colin Gubbins and revived in their post-war iteration.  For all their sophistication in terms of hidden hatches, ventilation systems and escape tunnel - providing accommodation for each patrol of eight men - the actual likely effectiveness of the OBs in action is often ignored.  The general conclusion of the leaders of the Auxiliary Units was that the men would have had a limited life expectancy of perhaps only 48 hours after they went into action.  Peter Fleming of XII Corps Observation Unit also feared that the OBs would  be quickly discovered once undergrowth died back in winter time. In use, therefore, although perhaps offering  reassurance to the patrol members, the chances of survival of the OBs would have been less than the sturdiness of their corrugated iron and brick construction now suggests.   

The effectiveness of the wartime OBs was never tested but their principle continued to be applied to Britain’s plans to defend against a Soviet invasion of Germany during the Cold War (a prime reason why research into the Auxiliary Units was initially discouraged). The SAS, Royal Armoured Corps Special Reconnaissance Squadron, Honourable Artillery Company and the Special Operation Post Troops of the Royal Artillery were all involved in the deployment of ‘Stay Behind Patrols’ (SBP) in north Germany at various periods into the 1980s, using buried hides for general surveillance and forward artillery fire direction.  The concept  of 'Stay Behind' forces by NATO during the Cold War is discussed in a useful article  'Eyes on Target by Tamir Sinai.  The principle was, during the first five days of a war  to provide  long-range reconnaissance, surveillance, and target acquisition (HQs, troop concentrations, artillery positions) and also undertake demolition work where bottlenecks were likely to occur in the enemy advance.  To achieve this, Stay Behind Patrols of typically four men would allow themselves to be bypassed by advancing Warsaw Pact troops, utilising pre-established underground hides and caches of arms, ammunition, and radios.  The hides were of two types. Prefabricated,  lightweight, 'T'-shaped MEXE modular shelters known as 'Ears' comprised a buried frame  made up of steel pickets, spacers and arch sections, covered with a jute fabric reinforced with a wire mesh, that supported an earth roof.  More substantial hides incorporated ‘I' beams that supported  a roof made from aluminium landing mats, able to bear the weight of a tank passing overhead. 

Continuing the Second World War division between such military Stay Behind Patrols and civilian resistance forces, agents of the latter (in similar terms to the Section VII resistance organisation in Britain) were instructed to survive an invasion, and to lay low  during any early occupation phases and only begin to operate (supplying intelligence, recruiting fighters and conducting sabotage operations) during the third phase of ‘every-day/routine occupation’.

In 1973 the non-too subtly titled Exercise Badger’s Lair was designed to test the vulnerability of hides built by 23 SAS over a period of three days on the Soltau training area in north Germany, using buried MEXE shelters. They were tested by new techniques of airborne thermal imaging and false colour photography (using Phantom jets and helicopters), by Direction Finding of radio transmissions and by more tradition foot search teams drawn from the  SAS and Parachute Regiments, some accompanied by RAF guard dogs. The searchers  were  looking for evidence of ground disturbance, the erection of wire aerials in trees or vehicle movements. Despite major technological advances since WW2, the most effective tool proved to be the sensitive noses of the dogs! The dogs had no specialist training other than first being allowed to identify the site of one hide, whose location was quickly found but then the dogs became confused as to the origin of  the scent.  Once the hidden SBP were ordered to open the hatch of the hide, the dogs immediately grasped the concept of the concealed target and had no further problems.  In all, 33% of hides were discovered in the first 20 minutes of the search, mainly by the dogs, who could identify the location of a hide from a distance of 100m downwind, with the evidence of an aerial in the trees being the next main give-away. (TNA DEFE 48/279). As a consequence, improved ventilation systems were introduced. 

The SBPs continued in use into the 1980s, by which time they were tasked with general surveillance of the enemy (SAS as Corps Patrol Units) and target acquisition for artillery (Honourable Artillery Company and later 5 Regiment Royal Artillery). In Exercise Temple Priest III (October – November 1983) the SBPs of 5 Regiment RA and HAC went to ground to test their ability to observe enemy vehicle movements and direct artillery fire.   They used both conventional aids such a binoculars with equipment not available in WW2 such as thermal imagers and video recorders. Observation was carried out either from self-contained observation posts (as also used by the Auxiliary Units), some distance from the hides or from the hides themselves. By now, protection for the occupants of the hides was provided by remote ground sensors, acoustic locators and miniature surveillance aids such as boroscopes and endoscopes..  These all gave the SBPs important warning of any potential compromising of their hide.  Typically sited at the edge of woodland, some posts had a field of view of 3km or more but the focus was on identifying targets on roads up to 2km away. The accuracy of identifying vehicle movements was between 50 – 80%, (TNA DEFE 48/1163)

Despite the technological advances in the post-war period it is salutary to recognise that the greatest danger to the security of the hides was that available to the Germans against the Auxiliary Units in 1940 – human eyesight and the noses of guard dogs (able to sniff out a hide in as little as 20 minutes).  In line with the assessments of Gubbins, Wilkinson and Fleming,  the vulnerability of the OBs suggests that once the Germans had been alerted to the presence of an Auxiliary Units patrol in a particular area through an attack on their primary target, they would not have long-survived any search. The Operational Bases of the Home Guard patrols of the Auxiliary Units did not have wireless communication so at least they were not at risk from the dipole aerials strung in the trees over the Special Duties Branch  IN Stations or bases of the army  Scout Patrols.  Those best protected were possibly  the OUT Stations of the Special Duties Branch, concealed under smelly chicken coops and the like, which would distract the dogs!

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