These were to be the main offensive weapons of the Auxunits, whose role was to attack the enemy's stores, transport and communications rather than his ground troops. Every Auxiliary received training in the basic principles of making and using explosive charges.
The basic charge consisting of one or two 4 or 8oz sticks of explosive required a detonator to fire it, this being either by a slow burning fuze, or a detonating fuze set off by a mechanical or timed device. A 'low speed' explosive, such as gelignite, could have its efficiency increased fourfold by the use of a suitable 'primer' such as a small amount of plastic (high speed) explosive or a knotted length of detonating fuze.
Detonators were small aluminium tubes, about 2in long and 1/8in wide, open at one end, and containing a very sensitive high explosive which exploded when heated. Commercial Bickford safety fuze (beloved by John Wayne and film makers generally!) was inserted into the open end of the detonator, crimped on with a special tool and when lit, burnt at a speed of two feet a minute, allowing time to walk a short distance from the charge.
Under operational conditions, a detonating fuze would have been used. These were proprietary brands such as Cordtex or Primacord which looked like a silver or yellow electric wire and which contained a white explosive filling. Detonating fuzes could set off individual charges or be used in a 'ring main' to link a series of unit charges for major acts of sabotage or demolition. On their own they could be used to cut and ignite the tin petrol cans likely to be found in petrol dumps or vehicle petrol tanks.
Patrols were issued with large quantities of explosives. Plastic High Explosive (PHE) was only then becoming available, and, despite supply shortages, Auxunits were favoured by a special issue of this, although its use in training was restricted to conserve supplies. The more common explosives were gelignite (which if handled with bare hands could produce a headache equal to a first class hangover!), blasting gelatine and Nobel's Explosive 808, with its distinctive smell of almonds. Some patrols had supplies of white 1 lb guncotton slabs, about the size of a thick paperback book. These had a central circular hole for the insertion of a purpose-made primer and detonator. Supplies of these were always sufficient to allow for their use in training, Auxiliaries practising their skills on disused railway lines and derelict vehicles.
The nature of their activities dictated that Auxunits would not stay around to witness the results of their explosive charges, and therefore the lighted safety fuze was only used for practice, and other equipment was provided for operational purposes.
The first of these was the time-pencil. This looked like, and was not much bigger than a metal propelling pencil, one end brass and the other end copper. The copper end contained a glass capsule of acid which, when the copper tube was compressed, broke, allowing the acid to eat through a fine copper wire, releasing a spring loaded striker which then hit a cap and detonator to explode the main charge. The copper wires were graded to provide five different time delays, varying from 30 minutes to 30 hours. Since the acid worked more slowly when cold, these times could vary by up to 80% and these pencils were notoriously inaccurate and unreliable. For this reason, Auxunits were instructed to use them in pairs and this was always done.
Another time mechanism was the L-Delay. This was invented by Churchill's 'think tank' team of 'Wheezes and Dodges". Looking like a shorter and fatter propelling pencil, it consisted of a green painted metal tube containing a spring loaded striker and detonating cap. When the safety pin was removed, the tension spring pulled on a soft alloy metal element, which gradually stretched until it broke, releasing the striker. It was easier to use and less sensitive to damp than the time pencil and slightly more efficient. The time delays were less, varying from 15 minutes to 12 hours depending on the thickness and composition of the metal element and the operating temperature when used
BOOBY TRAP MECHANISMS
Apart from using the 36M Grenade as a contrived booby trap, Auxiliary Units were issued with several special devices which could be used as a trap for the unwary or, given the right circumstances, as a self-induced act of sabotage.
The pull switch was a metal tube about 4 inches long containing a spring loaded striker head, held in place by a spring loaded release pin. When a pull of between 1 and 8lb was applied to this via a trip wire (a safety pin having been first removed) the striker would set off a percussion cap and detonator or detonating fuze to initiate a concealed explosive charge or mine.
A bracket was provided to enable the pull switch to be firmly attached to a tree or stake. When correctly installed, these were virtually foolproof. They could be adapted to enable charges to be fired electrically and it was possible to install them in such a way that, should the trip wire be discovered and cut, a further spring loaded wire would set off the explosive.
The pressure switch worked in a similar way, except that the spring loaded striker head was held in place by a thin soft metal spindle. A pressure of about 40lb on a shearing pin was sufficient to cut through this spindle, allowing the striker head to set off a cap, detonator or detonating fuze. Providing this switch was installed on a firm base, it could easily be sunk partially below ground, or the shear pin concealed by a light object which would not activate it until stepped upon.
Although not as common as pull and pressure switches, the spring loaded switch was a device which could be placed under a heavy object which, when removed, would set off a hidden charge.
'Stick Pencil' was the nickname given to another uncommon gadget, a metal tube buried in the ground, containing a firing pin and catch. A .303 cartridge could be inserted in such a way that, when the protruding bullet was stepped upon, it was discharged into the unfortunate's foot.
Under operational conditions, it was likely that all these devices would have been used as booby-traps and to give an early warning of intruders approaching operational bases.
Given the right sort of combustible target, a properly placed incendiary could do as much, if not more, damage to an enemy's stores and supplies as an explosive, and the Auxunits were supplied with a variety of equipment for this purpose, which could be used, either on its own or in conjunction with explosives for greater effect.
Magnesium Incendiary This was a black cylinder, 8in long and 2in in diameter containing powdered magnesium. It could be set off either instantaneously or by use of a time delay and it would burn for two minutes, giving off an intense heat and a dense smoke.
A.W. Bottle (76 Grenade) Also known as the S.I.P. (self- igniting phosphorus) bottle, this was simply a half-pint clear glass bottle filled with a mixture of kerosene and rubber, and phosphorus, separated f'rom
each other by a layer of water. The bottle was sealed with a 'Crown' cork, and when broken and the phosphorus exposed to the air, the contents ignited, giving off a foul smelling smoke and flame.
Although any fire could be extinguished with water, as soon as this dried up, the phosphorus would re-ignite. These were designed to be used as a fire and smoke grenade in vehicle ambushes, and a smaller version could be fired from a Northover projector. In storage, the crown corks were prone to corrosion, and a regular turn-over of supplies was recommended.
Pocket Time Incendiary These consisted of a flat black or mottled green celluloid casing, 3in by 5in, of three tubes joined together, the outer tubes containing thermite powder with a short length of slow burning fuze at one end. The central tube contained a delay device of acid and copper wire, like that of the time-pencil, which released a striker to light the match head and fuzes. The time delays were of the same order as those of time-pencils and, since these were subject to the same disadvantages of timing and unreliability, were recommended to be used in pairs.
Fire Pot This was a brown, waxed paper covered cylinder, 2 1/4in in diameter and 3in high, containing a very strong incendiary mixture. It could be ignited by any time delay or booby-trap and would then produce a powerful flame for one minute, after which it would burn more quietly for about 15 minutes, giving a hot local flame sufficiently intense to burst petrol tins.
Return to Auxunit News