Explosives Pack Finally, it is now known that most, if not all Aux Units were issued with a standard 'explosives pack', the contents of which was described in an appendix to a secret letter (Reference: AU/B/1/9a), dated 14 July 1944. It listed these contents: Appendix "B" to Secret letter Contents of One Aux.Unit Mark II. 24 Copper Tube Igniters. Notes. 1. Aux.Units Mk.II held in the Northumberland Area may be deficient of Copper Tube Igniters. 2. A large number of Aux.Units Mk.II will be deficient of 3-hr.L.Delays. Exact details are not obtainable but of the 360,000 which should be in circulation only 107,000 are actually contained in the Aux.Units, enumerated in Appendix "B". 3. A large proportion of the Aux.Units Mk.II will contain Magnets either Large or Small type. The number of these in each Aux.Unit will be about 6. SWITCHESPrepared by Aux Researcher Matthew Gibbs.One of the main strategies for the Auxiliary Units Operational Patrols was the destruction of enemy supplies and equipment. Much of their training related therefore to the carrying out of this aim. Explosives’ training took place with the Patrols and the Scout Sections, and was also concentrated on at Coleshill. At one typical weekend course at Coleshill House in 1941 Explosives training was the subject of a morning lecture from 0830 – 0925, then a practical session from 0930 – 1025 plus a further 55-min session on the Mills Grenade. That night was a practical patrol exercise that lasted at least 90 minutes where instructors would assess the patrols effectiveness. The following morning was a further hour slot for Explosives work. Quite a lot of information obviously relating to safety was provided, along with the strategies for the best places to attack and how to accomplish that. Explosive devices provided to the Auxiliary Units The explosives devices used by the Auxiliers can be simply
divided into three areas. Switches
The switch devices were numbered and also had a practical descriptive name, and are listed below:
Switch Number 1 Mk1 – Pull Switch. Attached to something like a trip wire, it operated when a pin on the switch was pulled. This allowed a striker pin to hit a percussion cap that triggered the fuse wire attached to it. Switch Number 2 Mark 1 – Pressure Switch. Placed under something or disguised with camouflage it operated when a sufficient weight pressed on the top. This sheared a metal pin attached to the spring-operated striker, which then triggered the explosives connected with it. Switch Number 3 Mark 1 – Release Switch. Placed inside or under something, this switch operated in reverse to the Pressure switch. When a weight was removed from it, or the closed part of the device released, for example the opening of a tin, this triggered the explosives connected to it. Often this was used by the army for booby traps. Switch Number 4 Mark 1 – Pull Switch – As per number 1 but simpler in operation. Switch Number 5 Mark 1 – Pressure Switch, operated as per number 2 but a different design. Switch Number 6 Mark 1 – Release Switch, operated as per Number 3 but a smaller, compact design, developed by SOE research for better concealment or for applications requiring a smaller device. Switch Number 8 AP – Anti Personnel switch, designed to be operated by weight and fired a pointed bullet up out of the ground into the foot of someone who trod on it. Switch Number 9 (as seen above) – L Delay, or Lead Delay. A Time Delay switch operating on the principle that a lead wire will stretch and break within a certain time at a certain temperature, which can be accurately calculated. The breaking of the wire inside caused a spring retained striker pin to set of a percussion cap and activate the explosives connected to it. These were supplied with a tag attached stating the number of hour’s delay before they would set off. Switch Number 10 – Time Pencil. A time delay switch operating on the principle that a certain strength of acid will eat through a fixed diameter copper wire within a certain time at a certain temperature. The corrosion of the wire inside the ‘pencil’ caused a spring retained striker pin to set of a percussion cap and activate the explosives connected to it. These were not as accurate as an L Delay but as they are extremely common to find it is likely that they were still fit for purpose within limits. They were supplied with a colour-coded tag that showed the number of hours delay they would provide. They also came with a temperature chart to indicate the tolerance to be prepared for. In extreme cold they would take longer to operate, and in extreme heat would work quicker.
Number 13 Switch (seen above) – a combination
Pressure, Pull, or Release device, which combined the trigger variations into one Universal Switch. B: Number 6 Switch C: Number 3 Switch D: Number 2 Switch E: Number 5 Switch with a spike extension fitted. Wire, Cord and Line Fuse Under this heading comes the equipment used to transfer the action of the switch to the explosive material. Sometimes this was dispensed with in some situations. L Delays, for example, were produced with could be fitted to a detonator or device [such as a Clam Mine] and used to set off explosives directly. Fuses, in military explosives, initiate the function of a made up charge or device. They are made up of some kind of burning material. Depending on their chemical design some will even work under water. One of the commonest is known as Safety Fuse or Bickford Fuse, named after its inventor. The ‘tube’ Safety Bickford Fuse or Fuse Wire This was procured by the military from civilian manufacturers who supplied the mining industry, such as I.C.I. Ltd. It was produced in slow and fast burning versions. The amount of time that it took for the fuse wire to burn down was measured in seconds per feet. According to the size of the explosive charge obviously the person firing it would want to be a certain distance away and so the time was a safety factor element allowing someone to get away, or be a certain distance away before the charge fired. More often than not the fuse is fitted into a detonator [blasting cap] which detonates and causes a chain reaction explosion in the explosive material itself. Safety fuse coating is usually black, commercial versions can be orange. Other military types are highly coloured and known as cords, explained later. The Bickford or Safety Fuse has a black powder core with a coating of ashphaltum or other waterproofing agent and a tough textile outer wrapper. It generally burns at 60 to 90 seconds per foot. Detonating Cord or Primacord Detonating cord differs from the above safety fuse because it is a very high speed which actually explodes rather than burns, and is used to detonate certain types of explosive without a separate detonator. Also known as Cordtex and Primacord, these are manufacturer trade names that have lapsed into common use. Its extremely high speed means it causes an almost instant detonation of the explosive once activated, over even quite long distances. For example one type is rated at 7,000 metres per second. This is not a light and then walk away fuse! |
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