The LRDG and their explosives:
As a general rule, patrols transported their explosives unarmed. That is: fuses and detonators were carried separately from the explosive devices to prevent accidental detonation. Even the Mills bombs, with the exception of a few needed for emergencies, were often carried with the fuses removed. When crossing the harsh desert terrain patrols often faced more dangers from shifting primed explosives than ambush.
An "Allways fuze" is an impact-only fuse. Basically it is weighted strip of cloth tape that would unravel when the grenade was thrown. Once unraveled the lead weight would pulled a safety pin which freed a bearing and armed the detonator. The grenade would then explode upon impact with any object or the ground. The term "Allways" refers to the fact that no matter how the grenade impacts, it will still explode.
The Allways Fuze
Developed by Jock Lewes, second in command of the SAS, the bomb was a one pound charge consisting of thermite, Nobel 808 plastic explosive. and a flammable liquid (motor oil). Using a delayed fuse, the charge was placed on enemy aircraft. The preferred location of placement was where the wing met the fuselage . This was thought to be the best place to cause the most damage. (Aircraft often had their fuel cells in the wings.)
The Lewes bomb came about because grenades and other explosive devices proved unreliable. Lewes' formula was a pound of plastic explosive, a quarter pound of thermite mixed with a bit of engine oil. Inside the mass was inserted a 2-ounce dry guncotton primer and detonator and a thirty-second fuse. The most common ignition method used was time pencils or pencil detonators. Others included release switches and pressure switches.
The Lewes bomb was a field expedient explosive. It is unclear what the container for the explosive was but it was probably a simple canvas sack or pouch coated with a sticky substance to ensure adherence to the surfaces. The bomb was usually placed and not thrown.
Plastic Explosive (Nobel 808)
Plastic Explosive is a type of explosive material that is stable over a wide temperature range, easily shaped by hand, and relatively stable, most types can be struck and /or burned with causing an explosion. The most common plastic explosive used by the British during World War II was developed by the Nobel Chemicals Ltd. and was commonly known as "Nobel 808". It looked like green Play-d oh and smelled faintly of almonds. During WW2 it was extensively used by the British Commandos, Royal Engineers and the Special Operations Executive (SOE) .
Timing Pencils were a cheap and effective fuze/detonator combination. One of the most commonly used was the N. 10 delay switch , or officially, "Switch, No. 10, Delay". The second most common was probably Switch, No. 9, L Delay; the "L".
The No. 10, delay, is made or a brass (and later aluminum) tube with a copper section at one end which contained a glass vial of a cupric chloride. Below the vial was a spring loaded striker held under tension. A thin metal wire kept the striker in place. To start the timer, the copper portion of the tube was crushed by striking, bending or otherwise denting it which in turn broke the vial of cupric chloride and the safety pen is removed. The cupric chloride would then eat away at the thin wire which would release the striker. The striker would then shoot down the brass tube, and hit the percussion cap which would ignite the detonator. This is turn would ignite the Nobel 808 or other explosive material. The length of delay was dependent on the concentration of cupric chloride; the more concentrated, the shorter the delay. Timing Pencils had delays from 10 minutes to 24 hours; however they were not accurate to the second. For instance a pencil with an hour delay may go off 2 or 3 minutes before or after that hour. At 12 hours, the delay may be as little as 11 hours or as much as 13 hours. Temperature and humidity would affect the length of delay.
The No. 11 was mechanical in nature consisting of a spring with a small notch cut into it. With the spring was put under tension it would begin to stretch. Eventually the spring would fail where it had been notched and the striker would be released. The No 11 was not as reliable as the No. 10 but because the No. 10 was not always water tight the No. 11 was normally first choice for underwater demolition. (Water could seep into the No. 10 pencil and dilute the cupric chloride possibly causing the detonator to fail.)
The pencils were normally issued five to a pack, with all five in the
pack being the same length of time. Typically when using the pencils,
two detonators would be placed in the explosive charge. The detonators
would normally come from two different stocks, if possible. This was done
in case one detonator failed.
More information on Explosive devices is forthcoming.